Pressure INCREASE due to added barrel length? [Archive] - Glock Talk

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Any Cal.
12-28-2011, 01:17
Starting this thread fresh to keep from cluttering 21 Carriers thread on the subject. Please, post up thoughts or experience you have on the subject. I am interested, and have an opinion, but will wait a bit for others to chime in first.

Yondering
12-28-2011, 11:44
I've also read on this forum that longer barrels cause higher pressure. Personally, I don't believe that; it doesn't make sense at all, if we're talking about Glock-length barrels. Pressure will exist in the barrel longer, of course, but peak pressure occurs long before the bullet exits, especially in a large bore cartridge with a relatively small charge of fast burning powder. Pressure is already dropping off by the time the bullet exits a G29 barrel; it's hard to picture why it would increase again if the barrel was longer.

(If we were talking about a very short barrel, then pressure might increase with length, up to a couple inches.)

I'll comment more later, but read this article: http://www.dtic.mil/ndia/2010armament/WednesdayCumberlandPhilipDater.pdf

Edit: OK, back now, so look at page 14 on the link above, where they show bore pressure at different barrel lengths. At 5", the pressure was already down to about 25,000 psi, from a cartridge that measured 55,000 psi peak pressure. This is from a round with a smaller bore and larger volume of powder than the 10mm; peak pressure happens in the 10mm sooner than it does in a 223/5.56.

TDC20
12-28-2011, 13:26
That was a really interesting article, Yondering. Thanks for posting that.

I also have to agree with Yondering. I don't think the barrel length will affect the peak pressure, which will occur long before a bullet exits a 4.6" barrel. Take a look at some pressure curves that XmmAUTO posted here:
http://glocktalk.com/forums/showthread.php?t=1372717

I created a spreadsheet that applies a theoretically linear pressure/acceleration (incorrect, I know, but it proves a point). This shows a 180gr. bullet leaving the barrel at 0.592ms for a 4.6" barrel and at 0.676ms for a 6" barrel. The 0.592ms corresponds fairly close to what XmmAUTO's ballistics program calculated for his 4.6" test barrel. The theoretical velocity for the 4.6" barrel on my spreadsheet was set to 1296fps by setting a certain pressure profile. This same pressure profile was then applied to a 6" barrel and yielded a theoretical velocity of 1480fps. Now, comparing ACTUAL measured velocities for ACTUAL 180gr ammo loaded to 1296fps from my 4.6" barrel, that actually yields 1400fps from my 6" barrel. What I believe this demonstrates is that the pressure is dropping rapidly as the bullet is traveling that last 1.4" of barrel. This isn't proving anything, because there are a lot of variables, but it does add support to the argument that barrel lengths are not a factor in peak pressure. Again, the plots from XmmAUTO's pressure measurements would also support this.

I will, however, end by saying this...all barrels are not created equally. There will be differences in chambering, bore dimensions, depth of rifling, surface roughness, etc. that can and will make differences in pressures when firing the same ammo in each. It's not an apples-to-apples comparison using a 4.6" Glock barrel vs. a 6" LWD barrel, but I don't want to confuse that with the primary issue here, which is strictly how barrel length affects pressure, all other factors being equal.

Any Cal.
12-28-2011, 13:53
I will say that I am of the opinion that barring some extreme circumstance, barrel length will not affect peak pressure in the least, unless it is a matter of the barrel being too SHORT for the powder to develop peak pressure. I will post some graphs later when I have time, so anyone that wants to can say otherwise.

21 carrier mentioned total average pressure, which could be related, but I will wait for him to chime in as well.

Gunnut80
12-28-2011, 15:41
I found the explanation mudrush gave: http://www.glocktalk.com/forums/showpost.php?p=17684398&postcount=33

He could be wrong but given his pressure testing equipment and the way he explained it I'm inclined to believe him.

Of course, as I said, he could be wrong.

And I wasn't meaning to be rude in 21Carrier's thread, Any Cal. No offense intended. I'm much better at talking than typing or writing!

Yondering
12-28-2011, 16:15
I'm very skeptical of mudrush's explanation. It sounds right at face value, until you look at the details closer.

-He says with Silvertip ammo, the pressure tops out at about 3.5 inches, but his slower powders build pressure up to 6". Problem is, the powders that work in a 10mm just aren't that slow. See the article linked above; the 5.56 uses much slower powders than anything that would work in the 10mm, but the pressure peak happens long before the bullet hits the 5" mark.

-He's saying the pressure is still at 37,000 psi when the bullet leaves a 4.6" barrel with his loads. If this were true, these would sound louder than most rifle rounds. The sound of the shot is related to the pressure released at the muzzle. 37,000 psi would be incredibly loud. The fact that the 10mm does not produce the sound levels that most high powered rifle rounds do, indicates that the pressure is lower when the bullet exits the barrel.

I'd like to see some actual pressure measurements with different barrel lengths in the 10mm. I suspect that mudrush made a calculation error in figuring out bullet distance traveled vs time.

Any Cal.
12-28-2011, 21:38
Alright, I've got a couple minutes. here are my thoughts, with some of the info that I base them on.

Take a look here at the chart that a guy drew up on Quickload. I realize that it isn't an actual measurement, but it shows pressure against bullet travel in inches...

(http://imageshack.us/photo/my-images/406/claysvs2400.gif/)


You can see that even with lots of a relatively slow powder, peak pressure happens very early in the cycle.

Now look here at Ballistics by the inch, and notice how the velocity jumps from 2" to 3", then less from 3-4, even less from 4-5, etc.

http://www.ballisticsbytheinch.com/10mm.html

If the pressure peaked at 5 or 6", then we would see drastic jumps in velocity of the same magnitude from 5-6", then a strong jump from 6-7", and so on, but we don't. All you see is a gradual decline in the rate of increase of velocity, as would be expected if the pressure peaked early in the barrel, like in the first inch or two.

As far as anecdotal evidence, if there was a pressure peak at 6" of barrel in handguns, you would see everyone shooting 6"+ barrels, as that length would get them into the jumps in velocity where each inch would be worth 1-200 FPS in a 10mm. What we see happening though, is that there are only marginal increases going from 4-5", less from 5-6", etc., to the point that an 8" barrel is pointless because the return on the length is so minimal.

If pressure peaks early in the barrel, then that leaves time of the bullet in the barrel to cause issues, and timing of the lockup to cause issues. If time in the barrel caused higher pressures, then why are the SAAMI specs for a cartridge the same, whether it is to be used in a pistol or rifle? If the rifle barrel works the brass too much due to the time in the barrel, then why aren't SAAMI specs dependent on barrel length? Shouldn't you be able to load .223 for an AR pistol much hotter, since the round would spend less time in the barrel? No, because the SAAMI spec is for Maximum pressure, not the time spent at pressure.

What about the lockup, perhaps the barrel is unlocking when pressure is high? That I don't know enough to talk about. I can say that the pressure in the gun when it unlocks is far less than the peak pressure that the brass must endure at the beginning, and that when pressures are high, the brass is pushed against the chamber walls, keeping it from moving. That being the case, if the extractor can pull the case out of the barrel, that means the pressure has already dropped considerably, letting the case spring back close to its original size. I can not guarantee it, but I believe that the pressure will not drop that far until the bullet has exited the barrel.

_Edit_ Looking at Yondering's PDF, the chart showing bore pressure vs. barrel length shows that at @ 5", that round had already developed peak pressure and was heading back down, and that was for a 5.56.

Sorry for the book, but I figure if I explain myself, you can show where one part or another is in error, if it is.

Gunnut-don't sweat it.

Yondering
12-29-2011, 10:31
http://www.ballisticsbytheinch.com/10mm.html



Cool link. That Buffalo Bore 180gr load is impressive!

BTW, I agree with your comments, I think we're on the same page here.

glock20c10mm
12-29-2011, 17:27
I'm very skeptical of mudrush's explanation. It sounds right at face value, until you look at the details closer.

-He says with Silvertip ammo, the pressure tops out at about 3.5 inches, but his slower powders build pressure up to 6". Problem is, the powders that work in a 10mm just aren't that slow.
:agree: Not much else to add to that!

What about the lockup, perhaps the barrel is unlocking when pressure is high?
In the 6" barrel realm my theory is that the above thought is dead on.

For all the powders that work from decent to super-good in 10mm Auto along with whatever combination of primer, COL, throat lead before rifling, and bullet, clearly we're all of the understanding that max pressure will be built up and just as quickly be dropping back down well before the bullet makes it beyond ~2" (after subtracting chamber length) of barrel length.

And again recalling some of Mudrush's posts, he more than a couple times also talked about heavier weight springs just for this reason in 4.6" barrels alone. Why the situation wouldn't be enhanced further with a 6" barrel is beyond me.

By the same token this is also just my THEORY at this point. I'ld suggest it's a pretty strong theory at this point though. And it sounds like some agree already. Anybody disagree???

Any Cal.
12-29-2011, 21:55
^^^ The problem is that I'm not sure about that statement. A good 'smith could say for sure, but if the lockup is held by the brass sticking to the chamber, then the action could not work until the pressure subsided (bullet left barrel). I don't know exactly how events are timed in that respect.

In any case, while it could cause issues, it wouldn't be an over pressure situation, it would be things like strange marks on the cases, or glock smiles that occured at a lower pressure, since the opening of the action would put the thinner portion of the brass out over the feedramp, rather than leaving the web over it. You would probably be able to see that if it was happening though, since the smiles would be higher up on the brass.

-Edit- After looking a few things up, I am pretty sure the barrel will stay locked up until the bullet exits. Consider this. At the start, barrel and slide are locked together, and the firing pin has forward momentum. At firing, the 135-220g bullet is being pushed forward by gas. The gas is being backed up by 20+ oz of mass, or easily 40x the weight of the bullet. As the bullet is traveling forward, it is also pushing against the barrel due to friction, which along with the recoil spring is helping the 20+oz of the slide stay in position. While the bullet is in the barrel, there is little reason for rearward motion of the pistol.

Once pressures have come up, the case is pushing against the chamber, which locks the slide and barrel together via the extractor/extractor groove. I don't think that the barrel and slide can unlock when pressures are high. If there was a need, it would be more likely for the extractor to rip a chunk out of the case head then to pull out a couple square inches of brass from the chamber, held in place by many thousands of PSI. It seems more reasonable to assume that the slide doesn't start it's rearward travel until the bullet has left the barrel, at which point there is no friction pulling the barrel forward, there has been time to overcome the mass of the slide, and the slide and barrel can unlock because pressure has dropped and the case is no longer sticking to the chamber.

I don't know if it is related, but it is said that you can compensate a pistol to the point that there is no longer enough recoil left to operate the gun. If that is the case, it means that the recoil is coming after the bullet leaves the barrel/comp, not while the bullet is still in the barrel.

glock20c10mm
12-29-2011, 23:31
^^^ The problem is that I'm not sure about that statement. A good 'smith could say for sure, but if the lockup is held by the brass sticking to the chamber, then the action could not work until the pressure subsided (bullet left barrel). I don't know exactly how events are timed in that respect.

In any case, while it could cause issues, it wouldn't be an over pressure situation, it would be things like strange marks on the cases, or glock smiles that occured at a lower pressure, since the opening of the action would put the thinner portion of the brass out over the feedramp, rather than leaving the web over it. You would probably be able to see that if it was happening though, since the smiles would be higher up on the brass.

-Edit- After looking a few things up, I am pretty sure the barrel will stay locked up until the bullet exits. Consider this. At the start, barrel and slide are locked together, and the firing pin has forward momentum. At firing, the 135-220g bullet is being pushed forward by gas. The gas is being backed up by 20+ oz of mass, or easily 40x the weight of the bullet. As the bullet is traveling forward, it is also pushing against the barrel due to friction, which along with the recoil spring is helping the 20+oz of the slide stay in position. While the bullet is in the barrel, there is little reason for rearward motion of the pistol.

Once pressures have come up, the case is pushing against the chamber, which locks the slide and barrel together via the extractor/extractor groove. I don't think that the barrel and slide can unlock when pressures are high. If there was a need, it would be more likely for the extractor to rip a chunk out of the case head then to pull out a couple square inches of brass from the chamber, held in place by many thousands of PSI. It seems more reasonable to assume that the slide doesn't start it's rearward travel until the bullet has left the barrel, at which point there is no friction pulling the barrel forward, there has been time to overcome the mass of the slide, and the slide and barrel can unlock because pressure has dropped and the case is no longer sticking to the chamber.

I don't know if it is related, but it is said that you can compensate a pistol to the point that there is no longer enough recoil left to operate the gun. If that is the case, it means that the recoil is coming after the bullet leaves the barrel/comp, not while the bullet is still in the barrel.
Well said!

There are still some basic facts involved. Namely that within ~2" of barrel I believe we know for a fact that max PSI has dissipated some and is continuing to dissipate really fast.

In my mind, one question remains. Does an additional 1.42" of true barrel length (4.6" VS 6.02") throw a wrench into what you said? I DON'T know. Not suggesting I do. I only continue to parrot it without know that same as you mentioned above; "I don't know exactly how events are timed in that respect." But what else is there?

And now you bring up another question in my mind. That is; Who actually has checked the specific location where any 10mm brass case has blown out in what would have been the 6'oclock chamber position in a Glock, against bad smiles in hot hot loads that didn't blow in that same position?

glock20c10mm
12-29-2011, 23:37
I just want to say I think it's great we're hashing this out. TYVM Any Cal. for starting this thread! IMO too many GT members are starting to practically throw their OPINIONS around as loose fact at a minimum regarding this specific subject. Not cool when none of us know for sure. Not YET anyway.

Here's to future knowledge - :cheers:

XmmAUTO
12-30-2011, 02:11
Here's my perspective on Pressure vs Barrel length vs Lockup

I'll start by saying that I'm no way a very educated person.

Lets start at Lockup:

It's my understanding that in a Browning designed short recoil system, the barrel and breech stay locked together until the bullet has left the barrel. Now looking at Newton's Third law every action has an equal and opposite reaction.This of course is how the slide mass is accelerated opposite the direction of the bullet. The question is when does the mass of the slide begin to accelerate? After googling " High speed camera 1911" there is footage that in my opinion shows that the bullet leaves the barrel before the mass of the slide begins to move. Think about it. Take a bullet and try to manually push it down a barrel from the chamber. It takes a lot of force to do. Why?
DRAG and FRICTION. It is my understanding that the bullet is literally keeping the barrel from moving rearward through a function of drag caused by friction until it exits. The remaining pressure acting on the base of the bullet and cartridge case exert the rearward force necessary for cycling the action.
Now in a straight blowback action the barrel remains fixed and the mass of the slide is directly acted upon by the force of pressure while the bullet is still in the bore as the two are not locked together. This is where we see movement of the case retarded by pressure.

Of course this is just my hypothesis.

Now on to pressure:

Pressure along with other variables is what gets velocity. This is where "There is no replacement for DISPLACEMENT". Larger caliber guns use pressure more efficiently. It's simple, more area for pressure to act upon. Hence a 10mm will never be a 500 S&W Magnum. Now in a small caliber just as in a small engine to get more power we increase pressure which in turn drives the smaller mass faster creating more energy. Think small 4 cylinder turbocharged high compression engine vs naturally aspirated big block v8.
The only drawback to increased pressure is being able to contain it without failure of the cartridge case, breach and chamber. This is why we are looking for FULLY supported chambers.

Now barrel length:

I would think that barrel length does play a role in pressure. In what way and how though, I don't know. I do know that peak pressure should be early in the cycle and taper off. How much pressure remains at bullet exit is dependent on a lot variables. When I get my test equipment up and running I'm sure we will learn more. I hope to also do testing in a 5", 6" and 10" barrel as well as a shorter G29 length barrel. Add up the cost and I'm looking at least another $1000 just in barrels. My project has been delayed and is taking time, please be patient.

On a side note please keep in mind that the test results I posted were not calibrated in any way.

21Carrier
12-30-2011, 04:40
On the pressure issue:

I think longer barrels do increase pressure, but total average pressure, not peak. Whether more overall pressure can smile brass or not, who knows. I saw a previously safe load almost blow up a gun when barrel length was increased. To be fair (and as TDC pointed out), there were too many variables for us to really gain any useful knowledge from that situation (though I had previously taken it as proof, I have settled down and thought about it more). First, the longer barrel was conventionally rifled. Beyond that, the chamber is tighter, which should make any expansion in the case head more pronounced. Even a difference in finish or the coefficient of friction in the barrel could make a HUGE difference in pressure.

At the end, I think a longer barrel increases total pressure, and I think any graph of time vs pressure should show that. The question is which smiles brass? Average pressure or peak pressure, or both?

On unlocking:

I think the gun starts to move the moment the bullet does. Remember, that does NOT mean that UNLOCKING begins at that moment. A Browning type action allows for some rearward movement before the barrel and slide unlock. Why do I think the barrel/slide start to move immediately? Well, what's causing them to move in the first place? They are moving rearward because the bullet got fired forward, right? So why would the slide and barrel not start moving at the same time? If they don't start to move until the bullet is gone, that doesn't make sense. How can the bullet move them if it's in the air 20 feet away? It can't. If the bullet is what's doing the moving, I'm pretty sure it has to happen while it's in the barrel. It just happens so fast, and the slide is moving so slowly in comparison, it seems like it's not moving.

I think I understand this right, but correct me if I'm wrong: We have two things going two opposite directions, and both should have the same momentum. Object one is the slide/barrel assembly (called S from now on), and object two is the bullet (called B from now on). Momentum is described by the equation p=mv, where P=momentum, m=mass, and v=velocity. Since momentum is always conserved, we know that both S and B must have equal momentum (S=B). However, because B's mass is so low in comparison to that of S, it creates a similar difference in velocity between the two. So if we throw some numbers in there, we get this:

m1=180gr bullet mass = 11.66g
m2=G20SF slide/barrel mass = 625g (guess based on 780g unloaded mass for whole gun)
v1=180gr bullet velocity = 1300fps
v2=G20SF slide/barrel velocity=?

(m1)(v1)=(m2)(v2)
(11.66)(1300)=(625)(v2) Solve for v2 and get 24.25fps as the velocity for the slide/barrel combination.

So that means the bullet is going 54 times as fast as the slide. What all this means to me is that even with slow motion video, it likely just LOOKS like the slide is not moving while the bullet's in the barrel. In the time that the bullet moves the roughly 3.5" down the barrel (discounting chamber length), the slide only moves .06". That's not enough for us to see in a video, so it LOOKS like it's not moving until the bullet is gone. Again, correct me if I'm wrong with my math above. It's been a while since I took Physics.

I am pretty sure that the slide/barrel HAS to move immediately. The slide NOT moving until the bullet leaves the barrel would seem to constitute a suspension of the laws of physics. If I understand the Browning short-recoil locking mechanism right, it does not mean that the slide/barrel is locked to the FRAME, but rather that they are locked TO EACH OTHER. They are able to freely slide along the frame as soon as the bullet moves, but they remain locked to each other, until the bullet leaves the barrel, and pressure lowers. You can see this by pushing on the muzzle of your Glock. The slide and barrel will move back about 1/8", while remaining locked together. After all, the brass being pressurized and all holds the slide and barrel together. That does nothing to hold the slide/barrel assembly in place on the frame. While in battery, the only thing that holds the slide forward is the recoil spring. You could weld the slide and barrel together, and you'd still be able to move the slide/barrel back that 1/8" or so until the barrel's lug hits the locking block.

Also, Mudrush was clear that he recommended stronger springs ONLY to make sure the slide was fully pushed into battery. If I remember correctly, he was not big on believing that stronger springs helped slow unlocking. He said it was just insurance to make sure the gun didn't fire while slightly out of battery.

nickE10mm
12-30-2011, 08:13
On the pressure issue:

I think longer barrels do increase pressure, but total average pressure, not peak. Whether more overall pressure can smile brass or not, who knows. I saw a previously safe load almost blow up a gun when barrel length was increased. To be fair (and as TDC pointed out), there were too many variables for us to really gain any useful knowledge from that situation (though I had previously taken it as proof, I have settled down and thought about it more). First, the longer barrel was conventionally rifled. Beyond that, the chamber is tighter, which should make any expansion in the case head more pronounced. Even a difference in finish or the coefficient of friction in the barrel could make a HUGE difference in pressure.

At the end, I think a longer barrel increases total pressure, and I think any graph of time vs pressure should show that. The question is which smiles brass? Average pressure or peak pressure, or both?

On unlocking:

I think the gun starts to move the moment the bullet does. Remember, that does NOT mean that UNLOCKING begins at that moment. A Browning type action allows for some rearward movement before the barrel and slide unlock. Why do I think the barrel/slide start to move immediately? Well, what's causing them to move in the first place? They are moving rearward because the bullet got fired forward, right? So why would the slide and barrel not start moving at the same time? If they don't start to move until the bullet is gone, that doesn't make sense. How can the bullet move them if it's in the air 20 feet away? It can't. If the bullet is what's doing the moving, I'm pretty sure it has to happen while it's in the barrel. It just happens so fast, and the slide is moving so slowly in comparison, it seems like it's not moving.

I think I understand this right, but correct me if I'm wrong: We have two things going two opposite directions, and both should have the same momentum. Object one is the slide/barrel assembly (called S from now on), and object two is the bullet (called B from now on). Momentum is described by the equation p=mv, where P=momentum, m=mass, and v=velocity. Since momentum is always conserved, we know that both S and B must have equal momentum (S=B). However, because B's mass is so low in comparison to that of S, it creates a similar difference in velocity between the two. So if we throw some numbers in there, we get this:

m1=180gr bullet mass = 11.66g
m2=G20SF slide/barrel mass = 625g (guess based on 780g unloaded mass for whole gun)
v1=180gr bullet velocity = 1300fps
v2=G20SF slide/barrel velocity=?

(m1)(v1)=(m2)(v2)
(11.66)(1300)=(625)(v2) Solve for v2 and get 24.25fps as the velocity for the slide/barrel combination.

So that means the bullet is going 54 times as fast as the slide. What all this means to me is that even with slow motion video, it likely just LOOKS like the slide is not moving while the bullet's in the barrel. In the time that the bullet moves the roughly 3.5" down the barrel (discounting chamber length), the slide only moves .06". That's not enough for us to see in a video, so it LOOKS like it's not moving until the bullet is gone. Again, correct me if I'm wrong with my math above. It's been a while since I took Physics.

I am pretty sure that the slide/barrel HAS to move immediately. The slide NOT moving until the bullet leaves the barrel would seem to constitute a suspension of the laws of physics. If I understand the Browning short-recoil locking mechanism right, it does not mean that the slide/barrel is locked to the FRAME, but rather that they are locked TO EACH OTHER. They are able to freely slide along the frame as soon as the bullet moves, but they remain locked to each other, until the bullet leaves the barrel, and pressure lowers. You can see this by pushing on the muzzle of your Glock. The slide and barrel will move back about 1/8", while remaining locked together. After all, the brass being pressurized and all holds the slide and barrel together. That does nothing to hold the slide/barrel assembly in place on the frame. While in battery, the only thing that holds the slide forward is the recoil spring. You could weld the slide and barrel together, and you'd still be able to move the slide/barrel back that 1/8" or so until the barrel's lug hits the locking block.

Also, Mudrush was clear that he recommended stronger springs ONLY to make sure the slide was fully pushed into battery. If I remember correctly, he was not big on believing that stronger springs helped slow unlocking. He said it was just insurance to make sure the gun didn't fire while slightly out of battery.

I believe your math is correct. Well said.

As for what Mudrush thought .... I kinda remember being in a thread talking about this very thing with him and he menitioned that it DID slow unlocking.... which I disagreed with. I did mention that a benefit of stronger springs would be to make sure the rounds were fully seated in the chamber to prevent a case rupture. (Glocks have a tendency to fire a TINY LITTLE BIT more out of battery than other designs: the 1911, for example. :))

Great thread and discussion. I've said it before and I'll say it again, I wanna see a test of someone running a hot load and getting brass smilies.... and then switching to a heavier spring setup and subsequently NOT getting smiles. That would help the "unlocking theory".... Until then, I'll stick with my premise that, while the heavier spring will help with other aspects of shooting hot loads, slide unlocking speed isn't one of them. The only thing that should slow this unlocking speed should be SLIDE MASS.

Taterhead
12-30-2011, 09:15
I believe your math is correct. Well said.

As for what Mudrush thought .... I kinda remember being in a thread talking about this very thing with him and he menitioned that it DID slow unlocking.... which I disagreed with. I did mention that a benefit of stronger springs would be to make sure the rounds were fully seated in the chamber to prevent a case rupture. (Glocks have a tendency to fire a TINY LITTLE BIT more out of battery than other designs: the 1911, for example. :))

Great thread and discussion. I've said it before and I'll say it again, I wanna see a test of someone running a hot load and getting brass smilies.... and then switching to a heavier spring setup and subsequently NOT getting smiles. That would help the "unlocking theory".... Until then, I'll stick with my premise that, while the heavier spring will help with other aspects of shooting hot loads, slide unlocking speed isn't one of them. The only thing that should slow this unlocking speed should be SLIDE MASS.
I remember in earlier postings that Mudrush claimed that heavier springs keep the slide and barrel locked together longer. Buffalo Bore claims this too. Later, Mudrush did seem to retract a bit from this theory, and later emphasized the desired positive return to battery that you mention.

Pressures and loads were clearly a work in process for Mudrush. It was very interesting to follow as he endeavored to apply theory to his real world business where the stakes were substantial.

Taterhead
12-30-2011, 09:56
Carrier, you explained the physics pretty much as I understand it. It has also been a long time since my last physics class so I might be missing something. I agree with Nick that I am skeptical about recoil spring weight influencing unlocking of the barrel and slide until you get to a spring weight of some substantial magnitude.

nickE10mm
12-30-2011, 10:06
...I agree with Nick that I am skeptical about recoil spring weight influencing unlocking of the barrel and slide until you get to a spring weight of some substantial magnitude.

Exactly.... because, at least it SEEMS, that the only way the spring would have any effect on unlocking is in its installed, (more of less) uncompressed state.... and even then, only due to the fact that it increases the friction of unlock due to the geometry of the barrel breech and lower lug .... Aside from that, the spring will only serve to DECELERATE the momentum already imparted on the rearward slide travel....

It would take a LOT of spring to make any discernible change in unlock speed if you ask me.

Of course, I have no idea and could be wrong..... Makes me wonder how much even JMB or Gaston even knew about this topic. Not exactly common knowledge.

XmmAUTO
12-30-2011, 11:23
Ok, After doing more reading I'll say that my above post was slightly flawed and that the slide/barrel mass will start to accelerate at the same time as the bullet. However there is still and frictional forces in play with regards to bullet and barrel. How much so? Not quite sure. I do know that when the bullet exits the barrel, the slide/barrel mass has not moved any appreciable amount as to cause a dangerous amount of unsupported cartridge case.
See pic https://picasaweb.google.com/lh/photo/s2Vkft-_NQSloHsB3ynCcNMTjNZETYmyPJy0liipFm0?feat=directlink

Say we take a theoretical slide/barrel mass to bullet ratio of 40:1 for the bullet to travel 4.6 Inches the slide/barrel will travel .115"

Also there is a primary and secondary recoil. One caused by the acceleration of the bullet and the other by acceleration of a small volume of high velocity gas at the moment of bullet exit.

It is correct that a recoil spring will not cause the slide to remain locked for a longer amount of time (in any amount that would be noticed). A higher spring rate will decelerate the slide faster. A 20# recoil spring is rated at full compression. As the spring is slightly compressed when installed there is a slight amount of force applied by the spring, maybe 2#?

Xmm

Any Cal.
12-30-2011, 11:36
21Carrier, maybe the barrel and slide DO move .06" while the bullet is in the barrel. It still doesn't change anything. Whether they do or not, there is also a lot of energy available in the expanding gases behind the bullet as it leaves the barrel. As soon as the bullet leaves the barrel(say .01" out), there are thousands of PSI pushing rearward on the casehead, so even if they hadn't started moving, they would be at that point.

Even if the barrel/slide are moving backwards, that doesn't mean the gun has unlocked. It can't until pressure comes down enough to let the brass shrink back down.

As far as average pressure or peak pressure deforming brass, look up some specs for brass and see what they are. If there is a time component in the specs, then average pressure would be something to consider. However, I think it much more likely that 37,500PSI would have a larger effect than an average pressure of 10,000PSI, or even 20,000PSI. The average pressure isnt nearly as high as the peak. Look at the chart I posted, that is with a lot of a fairly slow powder. Most loads in a 10mm will have much less area under the curve, so a lower average pressure.

Any Cal.
12-30-2011, 11:40
Ok, After doing more reading I'll say that my above post was slightly flawed and that the slide/barrel mass will start to accelerate at the same time as the bullet. However there is still and frictional forces in play with regards to bullet and barrel. How much so? Not quite sure. I do know that when the bullet exits the barrel, the slide/barrel mass has not moved any appreciable amount as to cause a dangerous amount of unsupported cartridge case.
See pic https://picasaweb.google.com/lh/photo/s2Vkft-_NQSloHsB3ynCcNMTjNZETYmyPJy0liipFm0?feat=directlink

Say we take a theoretical slide/barrel mass to bullet ratio of 40:1 for the bullet to travel 4.6 Inches the slide/barrel will travel .115"

Also there is a primary and secondary recoil. One caused by the acceleration of the bullet and the other by acceleration of a small volume of high velocity gas at the moment of bullet exit.

It is correct that a recoil spring will not cause the slide to remain locked for a longer amount of time (in any amount that would be noticed). A higher spring rate will decelerate the slide faster. A 20# recoil spring is rated at full compression. As the spring is slightly compressed when installed there is a slight amount of force applied by the spring, maybe 2#?

Xmm

There was a discussion on Google groups regarding bullet POI change due to bullet weight in 1911s, and this is the basic math that was used. Seemed like a pretty sharp guy, and I have been trying to remember how he put things. The first few paragraphs were exactly what he said. Also, that the rocket effect added a considerable amount of recoil; the speed of the gasses were such that their kinetic energy was quite high, meaning all that energy was pushing backward as well.

Yondering
12-30-2011, 11:41
Since momentum is always conserved, we know that both S and B must have equal momentum (S=B).

No. Energy is always conserved, not momentum. (Momentum is conserved within a closed system; what we're talking about here is not.) You can do a similar calculation, but based on energy, then factor in energy losses from friction, and energy absorbed by the recoil spring, and the shooter's hands. You'll also have to include energy input from the powder gasses, which you didn't include in your momentum equation either.

Any Cal.
12-30-2011, 11:43
Of course, I have no idea and could be wrong..... Makes me wonder how much even JMB or Gaston even knew about this topic. Not exactly common knowledge.

They probably went out to a shop and built a "gun" in a fixture with a handful of springs and bullet weights to try out. They could have had an idea of what was going on in a few hours or less, just by watching how things worked. Just a few experiments could tell them how much recoil energy they had to work with, and whether springs or mass would do more good.

Yondering
12-30-2011, 11:45
Exactly.... because, at least it SEEMS, that the only way the spring would have any effect on unlocking is in its installed, (more of less) uncompressed state....

No. Why would you think the spring is uncompressed in it's installed state? Have you never disassembled your glock? Just because the spring is captured, does not make it uncompressed. Look at the length of an uncaptured spring, and the length of an installed spring.

A 20# recoil spring ... As the spring is slightly compressed when installed there is a slight amount of force applied by the spring, maybe 2#?

Xmm

Again, no. Pull back on your slide a little with the gun assembled. There's certainly more than 2# of pressure, even with a fairly light spring.

In a 1911, most recoil springs exert about the same force in their installed state, but have different spring rates. I haven't found this to be the same in Glocks. I have 17 and 24 lb springs here on my bench; the 24 lb spring clearly exerts more force in the installed state. It's also compressed to about 1/3 of it's free length when installed. I've run a bunch of 1911 springs through our spring tester at work, but haven't had a chance to do so with my Glock springs.

Because a heavier spring does exert more force on the slide at rest, it will help delay unlocking slightly. The effect may be small enough to be insignificant, I'll have to study this further.

nickE10mm
12-30-2011, 12:33
No. Why would you think the spring is uncompressed in it's installed state? Have you never disassembled your glock? Just because the spring is captured, does not make it uncompressed. Look at the length of an uncaptured spring, and the length of an installed spring.


I was speaking in relative terms. The spring weight seems to me to be insignificant in keeping the barrel/slide locked.

Yondering
12-30-2011, 12:47
I was speaking in relative terms. The spring weight seems to me to be insignificant in keeping the barrel/slide locked.

I'll post a chart of a few Glock spring weights next week.

Any force holding the slide closed will delay unlocking; it doesn't take much. You can keep it locked up by pressing your palm against the back of the slide.

nickE10mm
12-30-2011, 12:58
Interesting thread here. 1911Tuner is an extremely knowledgeable smith on (several) boards on the net ... Granted, they are speaking of the HiPower and 1911, but the concepts are similar.

http://www.thehighroad.org/archive/index.php/t-203056.html

Another interesting quote I found on the .460 Rowland Wiki page ....

Conversions
Model 1911 pistol with .460 Rowland conversion from Clark Custom Guns. The 1.5" compensator works in conjunction with a 24 pound recoil spring to control the recoil.

M1911 autoloaders converted for this cartridge require a compensator.[citation needed] The increase in slide velocity over a standard .45 ACP, or even a .45 Super round, cannot be properly controlled with an increase in recoil spring rate alone. A conversion requires a compensator to delay unlocking of the M1911 action until pressure has fallen to more manageable levels. Without a compensator, slide or frame failure would result.[citation needed]

Conversion kits co-developed by Wild West Guns and Jonny Rowland for the Smith & Wesson M&P, Glock and Springfield Armory Tactical striker type pistols, due to locking system differences, do not require use of a compensator. Slide velocity in these converted firearms is controlled with a change to the recoil spring alone. Subsequently, the converted firearm is lighter and more compact than a converted 1911 type.

Basically, they are saying that the recoil systems are inherently different with 1911's versus Glocks .... and I've found this to be the case. It almost seems like the recoil spring change alone in a GLOCK might have more effect on unlocking than it would in a 1911. Hmmm

glock20c10mm
12-30-2011, 13:58
Pressure INCREASE due to added barrel length?
Back to this original question...after further thought; after the initial pressure spike to get the bullet moving, the pressure will not increase with more barrel length. What will increase is gas volume per burning propellant up until any point propellant has been burned completely with no more to burn.
Why do I think the barrel/slide start to move immediately? Well, what's causing them to move in the first place? They are moving rearward because the bullet got fired forward, right?

I don't think so (I used to up until minutes ago :supergrin:). I believe that's the easiest thing for most of our minds to grasp with our limited knowledge of the subject(s) at hand, but we also KNOW there is plenty more going on than just the bullet moving forward. ie, stuff is going on to move AND continue to accelerate the bullet forward.

The bullet isn't just moving forward. It's accelerating forward. Why is it accelerating? Because of a greater and greater build up of gas volume behind the bullet from burning powder creating a larger and larger volume of hot gas until all powder has been burnt.

In the mean time there is pressure. And that's takes me to what Any Cal. has touched on below...
...there is also a lot of energy available in the expanding gases behind the bullet as it leaves the barrel. As soon as the bullet leaves the barrel(say .01" out), there are thousands of PSI pushing rearward on the casehead, so even if they hadn't started moving, they would be at that point.
If a force is pushing the bullet forward and continuing to accelerate the bullet forward, doesn't there have to be an equal force pushing rearward and outward, equal to the force that's continuing to build and accelerate the bullet forward untill the bullet leaves the barrel?

If that's the case, and I don't see how it couldn't be :dunno:, then why would any part of the gun or shooter move till the bullet is gone, when all that's left is rearward and outward force, which would then initiate recoil, and maybe or maybe not slide/recoil-spring action?

In other words I'm suggesting that the force causing the momentum of the bullet moving and accelerating forward are canceled out by equal rearward and outward force all happening at the same time till the bullet is gone, at which point all that's left, and first initiates recoil and probably slide/recoil-spring action, is force by pressure left over not yet dissipated, with the only thing left to act on being the platform the cartridge was fired from.
Even if the barrel/slide are moving backwards, that doesn't mean the gun has unlocked. It can't until pressure comes down enough to let the brass shrink back down.
I feel I agree with this but just want to add that I don't believe any of it would happen till the bullet is out of the barrel. If it did, wouldn't pressure already have dropped low enough for the brass cartridge case to contract and allow gas volume under pressure to leak backward behind the brass case? I would think so, but don't know.

In other words I feel the brass case probably doesn't contract from the chamber walls till the bullet is gone either, no matter the barrel length, but keeping the conversation relative to barrels lengths of around 3" to 15".

Any Cal.
12-30-2011, 20:40
The post by 1911Tuner was very good, and basically says that the barrel and slide will start moving while the bullet is in the barrel, and that while a recoil spring shouldn't matter, at times it will if there are extenuating circumstances. And if Tuner says the world is flat, I would just bank on that. :D

The slide and barrel ARE moving while the bullet is in the barrel, but they aren't moving far, and they shouldn't be unlocking in most cases. As XmmAuto pointed out, the slide could move an amount similar to its difference in weight compared to the bullet, i.e, 1/40th or 1/50th of the bullet travel. That is similar to the argument made in the Google group I mentioned earlier.

As to whether it matters as far as a pressure peak due to a longer barrel, I don't think it does. We are not working at peak pressure any more, or anywhere close to it. Whether or not there was more pressure when the gun tried to unlock would have nothing to do with the expansion of the brass. Also, according to Tuner's post, the gun cannot unlock until pressure drops to ambient, i.e, the bullet has left the barrel, except in certain circumstances. Another issue is that the longer barrel will have more weight to it, and the weight will be in the front end, both of which would act to delay unlocking to an extent.

I'm thinking that any pressure increase upon a switch to a longer barrel would have to be from some other source, but I can't disprove 21Carrier's theory as to more time under the pressure curve being the culprit, so it can't be ruled out yet.

_The_Shadow
12-30-2011, 21:45
The swing link of the 1911 pistol is what locks it into battery, if the link is bad it will unlock was my understanding. I have read where the 1911 with the link could be fired without a recoil spring in place, the gun would maintain lock until the bullet left the barrel. Not sure if this is true, but it was stated!
http://www.m1911.org/locking.htm

Bullet travling thru the barrel acts to pull the barrel forward to keep it locked, but the moment the bullet is free of the bore, the pressure present exerts the force needed to over come the recoil spring and complete the slide cycle to unlock and eject the spent casing with the recoil spring returning the slide and fresh round to battery!

http://www.youtube.com/watch?v=Lh-nrwQlAd8

Rounds with an impulse stronger that the locking and recoil system can over come the workings in my opinion!

Any Cal.
12-31-2011, 00:14
Nice chart, Shadow. The barrel link on a 1911 pushes the locking lugs of the barrel into mating grooves in the frame to lock the gun up. If the link was too small, the lugs would not engage, leaving the slide and barrel separate.

FWIW, I believe the locking lugs on the 1911 are analogous to the mating of the square portion of the barrel in a Glock, where the barrel and slide are locked together, and the barrel link on a 1911 serves the same purpose as the locking block and the ramp on the underside of the barrel on a Glock. Same system, just a different means of carrying it out.

21Carrier
12-31-2011, 03:29
Guys, this is getting ridiculous (but funny). We are like blind men sword fighting. We all keep destroying each others' theories, and shooting down each others' fuzzy math. It has been interesting, and I put my ideas out there. Short of consulting a Physics guru, I think it's just gonna be friendly arguing with no real consensus. I doubt we will learn anything in the end. Anyone have a friend in the Physics field? Until then, I'm checking out. I love learning, but I am not sure that's what's happening here. You boys be good.

:duel:

Oh yeah, one last thing. I think one of the things that contributed to my particular problem (moving a hot, safe load from G29 to G20LS and getting a near KB) was the fact that I was getting a full burn in the longer barrel.

nickE10mm
12-31-2011, 06:00
Guys, this is getting ridiculous (but funny). We are like blind men sword fighting.

Aye, laddy. We are

tlrgsxr
12-31-2011, 06:50
Spring strength will affect the unlocking of a Glock or 1911 pistol. Picture it with no spring allowing the least resistance to the slides movement to a solid obstruction providing the most resistance to the slides movement (none). Varying strength springs are somewhere in between and will determine the amount of time it takes to move.

The reason why this is irrelevant for the purpose of changing the lock time is because the distance for the unlocking is so short. To change the lock time with any significance would require a spring that provided significant strength while being compressed very little and would offer so much resistance that the pistol wouldn't function.

Does this make sense?

Any Cal.
12-31-2011, 10:20
:duel:

Oh yeah, one last thing. I think one of the things that contributed to my particular problem (moving a hot, safe load from G29 to G20LS and getting a near KB) was the fact that I was getting a full burn in the longer barrel.

We don't know a whole lot, but we do know that you were getting a full burn in your G29 unless you were using a magnum rifle powder.

Yondering
12-31-2011, 10:46
Oh yeah, one last thing. I think one of the things that contributed to my particular problem (moving a hot, safe load from G29 to G20LS and getting a near KB) was the fact that I was getting a full burn in the longer barrel.

This goes straight back to the original topic - you still think pressure continued to build as powder burned in your longer barrel? Unless you were getting some sort of secondary pressure spike (bad powder or primer choice?), that's pretty unlikely.

As you said yourself, there were too many other differences between your two barrels to claim that barrel length had anything to do with raising pressure.

A much more logical explanation is you used a load that was safe in the large glock chamber, and fired it in a tight chamber. A tighter chamber gives a smaller combustion chamber volume, same as seating the bullet deeper. Pressure goes up, sometimes way up. Throat length makes a big difference too, a tight throat increases chamber pressure. Barrel length has nothing to do with it. Neither does spring weight or action timing either, not sure how we got on that subject.

Taterhead
12-31-2011, 12:05
Spring strength will affect the unlocking of a Glock or 1911 pistol. Picture it with no spring allowing the least resistance to the slides movement to a solid obstruction providing the most resistance to the slides movement (none). Varying strength springs are somewhere in between and will determine the amount of time it takes to move.

The reason why this is irrelevant for the purpose of changing the lock time is because the distance for the unlocking is so short. To change the lock time with any significance would require a spring that provided significant strength while being compressed very little and would offer so much resistance that the pistol wouldn't function.

Does this make sense?

Sort of. This would imply that there would be zero lockup if there was no spring at all. However, we know that lockup would occur without a spring (assuming starting from full battery). The bullet traveling down the barrel causes the barrel to jam forward against the slide thus keeping it locked.

We are going to need some slomo video in a controlled environment to know for sure.

glock20c10mm
12-31-2011, 13:51
This goes straight back to the original topic - you still think pressure continued to build as powder burned in your longer barrel? Unless you were getting some sort of secondary pressure spike (bad powder or primer choice?), that's pretty unlikely.

As you said yourself, there were too many other differences between your two barrels to claim that barrel length had anything to do with raising pressure.

A much more logical explanation is you used a load that was safe in the large glock chamber, and fired it in a tight chamber. A tighter chamber gives a smaller combustion chamber volume, same as seating the bullet deeper. Pressure goes up, sometimes way up. Throat length makes a big difference too, a tight throat increases chamber pressure. Barrel length has nothing to do with it. Neither does spring weight or action timing either, not sure how we got on that subject.
I would think Yondering has to be correct here.

Actual PSI is going to be greatest somewhere between getting initial movement from the bullet and the bullet initially engaging the rifling of the barrel.

After that fagetabotit. PSI drops and drops fast, evidenced by the bullet continuing to accelerate less and less as it get farther down the barrel. Think about the PSI it takes to accelerate the bullet from ZERO FPS to 1100 FPS (750 MPH:supergrin:) and engage rifling while that's going on, as opposed to accelerating from 1100 FPS to 1300-1350 upon exiting the barrel.

Unless that bullet runs into a barrel obstruction beyond first engaging the rifling, or the barrel is bent after the point the bullet first engages the rifling, or whatever else goofy stuff we know we don't want going on, the pressure does not rise in a longer barrel over that of a shorter barrel.

Hot Gas Volume becomes greater as long as there is still powder to burn, but once that bullet is a little bit down the barrel that gas volume never becomes great enough again to raise PSI beyond what it took to get the bullet moving in the first place up to the point the rifling is engaged.

21Carrier; The full burn in the longer barrel has nothing to do with it. A tighter chamber in addition to no better 6'oclock chamber support than a stock G29 barrel is more than likely your culprit. About the only other thing it could be is a barrel so faulty that it's dimensions are overly constrictive for the bullet diameter.

tlrgsxr
12-31-2011, 17:23
This would imply that there would be zero lockup if there was no spring at all.

No, actually it doesn't. Please re-read it.

If you still don't believe me or if you just want to learn more about recoil springs I'll suggest George Chinn's - Design Analysis of Automatic Firing Mechanisms, 1955 and the US Army's Engineering Design Handbook AMCP 706-260, 1970.

My previous comments are correct, believe it or not. Again... To change the lock time with any significance would require a spring that provided significant strength while being compressed very little and would offer so much resistance that the pistol wouldn't function.

nickE10mm
01-08-2012, 13:23
Fwiw, I've got a Wolff 20lb spring / rod combo in it way to me and I'm gonna find out what a recoil spring does to lock up the next time I chrono some loads. Will try and test both the Glock stock vs Wolff and the Fusion with 20-24lb springs with both low and very hot ammo. We'll see how it affects both velocity AND bulge.

Taterhead
01-08-2012, 15:23
No, actually it doesn't. Please re-read it.

If you still don't believe me or if you just want to learn more about recoil springs I'll suggest George Chinn's - Design Analysis of Automatic Firing Mechanisms, 1955 and the US Army's Engineering Design Handbook AMCP 706-260, 1970.

My previous comments are correct, believe it or not. Again... To change the lock time with any significance would require a spring that provided significant strength while being compressed very little and would offer so much resistance that the pistol wouldn't function.

I re-read your other post 3-4 more times. Having done that I realize that I misunderstood your thoughts. I get what you are saying now, although it wasn't super clear the first pass through. Your comments echo remarks that I wrote earlier on the subject. Thanks for straightening me out.

Yondering
01-08-2012, 16:39
Fwiw, I've got a Wolff 20lb spring / rod combo in it way to me and I'm gonna find out what a recoil spring does to lock up the next time I chrono some loads. Will try and test both the Glock stock vs Wolff and the Fusion with 20-24lb springs with both low and very hot ammo. We'll see how it affects both velocity AND bulge.

Let us know your results. I suspect you wont' find any difference in velocity, and especially no difference in case bulging; the barrel would have to completely unlock from the slide to allow more case bulging. (In a blowback action, cases will bulge more with weaker springs or hotter loads, but that's different.)

FWIW, sort of an interesting side note related to spring weights; on Friday I tested some of my Glock recoil springs in a spring tester, and found that my 24 lb ISMI spring is actually the same rate as a new Glock OEM spring, 17 lbs. Don't know if they just sent me the wrong spring or what. The uncompressed length was quite a bit longer than the stock spring, but the numbers indicate it's not any stiffer. I'll be asking for a replacement though.

EDIT: Looks like they just sent me the wrong spring. I'll post more when I get a replacement.

Taterhead
01-08-2012, 17:13
Let us know your results. I suspect you wont' find any difference in velocity, and especially no difference in case bulging; the barrel would have to completely unlock from the slide to allow more case bulging. (In a blowback action, cases will bulge more with weaker springs or hotter loads, but that's different.)

FWIW, sort of an interesting side note related to spring weights; on Friday I tested some of my Glock recoil springs in a spring tester, and found that my 24 lb ISMI spring is actually the same rate as a new Glock OEM spring, 17 lbs. Don't know if they just sent me the wrong spring or what. The uncompressed length was quite a bit longer than the stock spring, but the numbers indicate it's not any stiffer. I'll be asking for a replacement though.

Interesting.

My 22# Wolf certainly feels more tightly sprung when I rack the slide - by a long ways.

I have been curious about how spring weight is measured. At full compression, mid compression, partial compression? How does a spring tester work?

Yondering
01-08-2012, 17:37
Interesting.

My 22# Wolf certainly feels more tightly sprung when I rack the slide - by a long ways.

I have been curious about how spring weight is measured. At full compression, mid compression, partial compression? How does a spring tester work?

Advertised spring weight is the force the spring applies with the slide all the way back. As you might guess, this says nothing about the actual spring rate, or the spring force when the slide is closed. Stock is 17 lb with the slide back, and about 7 lb with the slide forward.

My spring tester records load and displacement, in very small increments. It uses an electric motor to compress the spring while recording data from a load cell and an LVDT. I can then plot that data in a chart to compare different springs. I set it up to start at the "slide closed" length, and stop at the "slide open" spring length. (As measured on my G21)

I'll post some spring data after I mess around with it a bit more. If you (or anyone here) has a certain spring you want tested, let me know.

tlrgsxr
01-08-2012, 18:48
As per my previous posts, I'm not sure what you guys are expecting in the amount of increase lock time using a heavier spring. Using the formulas in the reference materials I mentioned, I created an Excel sheet that using inputs like bullet speed, weight, charge weight, exit gas velocity, bolt (slide& barrel) weight, spring rate, initial spring force, etc calculates things like lock time, recoil time, energy at full stroke, and so on.

Using some guesstimates, I'm calculating an increase in lock time of only slightly more than 1% while using a 22# spring versus stock. Using the same guesstimates, in order to see a significant difference, like 10% in lock time, would require approximately a 50# spring. If someone can post accurate weights for the barrel and slide (I guessed), an example of the ammo to include bullet weight, charge weight, and velocity (I used one off the internet), and some measure spring rates (I calculated mine), I can post the results for anyone that's interested.

Yondering
01-08-2012, 22:20
Using some guesstimates, I'm calculating an increase in lock time of only slightly more than 1% while using a 22# spring versus stock.

Out of curiosity, what spring force did you use in your spreadsheet? Stock springs are 17 lb, but only push about 7 lb with the slide closed. I don't know what a 22 lb spring pushes with the slide closed.

I think that the general idea of your calculations is correct though, that the spring weight won't make a significant difference in lock time.

Any Cal.
01-08-2012, 22:49
As per my previous posts, I'm not sure what you guys are expecting in the amount of increase lock time using a heavier spring. Using the formulas in the reference materials I mentioned, I created an Excel sheet that using inputs like bullet speed, weight, charge weight, exit gas velocity, bolt (slide& barrel) weight, spring rate, initial spring force, etc calculates things like lock time, recoil time, energy at full stroke, and so on.

Using some guesstimates, I'm calculating an increase in lock time of only slightly more than 1% while using a 22# spring versus stock. Using the same guesstimates, in order to see a significant difference, like 10% in lock time, would require approximately a 50# spring. If someone can post accurate weights for the barrel and slide (I guessed), an example of the ammo to include bullet weight, charge weight, and velocity (I used one off the internet), and some measure spring rates (I calculated mine), I can post the results for anyone that's interested.

Loaded slide and barrel weigh about 21 3/4 oz.

An example of ammo would be 220 @ 1140 for Buffalo Bore in a stock G20, maybe give it a charge weight of 13g powder, which shouldn't be too far off. I am hoping someone else can weigh a case, I don't feel like running outside to check.

I'm glad someone else is taking this on. I was just talking to an engineer buddy about working on it with me earlier tonight.

If you can do it easily, it would also be nice to know
1) how much difference there is in remaining energy or speed in the slide when it is fully open after firing due to various spring weights,
2) the slide speed on return to battery at various spring weights, and
3) How comparable an added oz or two on the slide would be to a heavier spring weight in reference to lock time.

I guess (3) would not matter if even a heavy load was not enough to get the gun to try to unlock before the bullet had left the barrel, and I assume that all of the numbers would be approximate, as the strength of the shooters grip might have decent impact on slide speed nearing fully open and on the way back.

Any Cal.
01-08-2012, 22:58
Out of curiosity, what spring force did you use in your spreadsheet? Stock springs are 17 lb, but only push about 7 lb with the slide closed. I don't know what a 22 lb spring pushes with the slide closed.

I think that the general idea of your calculations is correct though, that the spring weight won't make a significant difference in lock time.

It seems like there could also be variation between manufacturers, and the way they label their product. Some might measure spring pressure when fully compressed, others may measure when in the shortest working position, etc. Not that that would invalidate anyone's argument, but it could make it difficult to say "A 22# spring does ______". I guess we would know better once you've measured a couple. -Edit-Just saw your post about the ISMI spring vs. stock. That is kind of what I was getting at, if they hadn't just sent you the wrong one. If they are measured in different ways, then the label isn't worth all that much. Even if they are all using the shortest working position, if they don't all get there the same way, there would be a differences in the way they affected the way the gun worked. One could have more or less pressure than the next when the slide was closed, and the amount of energy they had resisted could be considerably different at the midpoint of the slide's travel.

If you come up with the neutral length of the stock spring, or some of the other fancy #s for it, please post them up.

nickE10mm
01-09-2012, 10:57
Let us know your results. I suspect you wont' find any difference in velocity, and especially no difference in case bulging; the barrel would have to completely unlock from the slide to allow more case bulging. (In a blowback action, cases will bulge more with weaker springs or hotter loads, but that's different.)

FWIW, sort of an interesting side note related to spring weights; on Friday I tested some of my Glock recoil springs in a spring tester, and found that my 24 lb ISMI spring is actually the same rate as a new Glock OEM spring, 17 lbs. Don't know if they just sent me the wrong spring or what. The uncompressed length was quite a bit longer than the stock spring, but the numbers indicate it's not any stiffer. I'll be asking for a replacement though.

I agree 100%, however, the rumors around here are getting annoying and I'd like some real data, if for nothing else, to get the info out there. The test will be impartial, however.

nickE10mm
01-09-2012, 10:58
As per my previous posts, I'm not sure what you guys are expecting in the amount of increase lock time using a heavier spring. Using the formulas in the reference materials I mentioned, I created an Excel sheet that using inputs like bullet speed, weight, charge weight, exit gas velocity, bolt (slide& barrel) weight, spring rate, initial spring force, etc calculates things like lock time, recoil time, energy at full stroke, and so on.

Using some guesstimates, I'm calculating an increase in lock time of only slightly more than 1% while using a 22# spring versus stock. Using the same guesstimates, in order to see a significant difference, like 10% in lock time, would require approximately a 50# spring. If someone can post accurate weights for the barrel and slide (I guessed), an example of the ammo to include bullet weight, charge weight, and velocity (I used one off the internet), and some measure spring rates (I calculated mine), I can post the results for anyone that's interested.

Fascinating. I've heard and said this a million times (that a spring shouldnt make any discernible difference) but I'd never seen any post from you with the above info until now. Cool stuff. Makes total sense.

tlrgsxr
01-09-2012, 20:00
For my previous post, I used 3.35lb/in for the stock spring rate based on some measurements I took of a spring. In hindsight, it may have been well used as it has an initial force of 9lb and a max of 13, well short of the published 17#.

That said, for these purposes I need an accurate spring rate, free length, installed length, and installed "compressed" length. I believe I used 3.15" as the installed length and 1.18" as the installed "compressed" length. Someone can measure their G20 and confirm my numbers. So, all that's left is the spring free length and the spring rate... Yondering? With it we can calculate the spring preload at its installed length as well as the maximum load at the installed "compressed" length with the slide at its most rearward position.

As per Yondering's post (#42) spring manufacturers may not be changing the rate from stock, but the free length and as a result, the preload and the max load, then using the max load # to claim it's a 22# spring (or whatever). There is a difference.You'll note, the ISMI Glock 19 springs go coilbound before the slide is retracted all the way. This has me wondering if they're not changing the rate at all.

Any Cal, I'll use the other numbers you've provided and can calculate all 3 items you asked about.

NickE10mm, your assessment is correct, changing the spring rate will have negligible affect on lock time. Hopefully, we can put this to rest shortly with some scientific numbers to back it up and then move on.

That said, there's other ways to increase lock time, for example, Any Cal alluded to increasing slide/barrel weight. He's correct and I can provide some calculations. In addition, I'm no firearms engineer and I honestly haven't thought this through, but why not change the locking lugs on the barrel? I'm sure I'm missing something, but... The barrel and slide move only 3mm before unlocking begins. If one were to machine the backside of the forward lug by only 1mm, allowing 4mm of travel, the lock time would be increased by a whopping 33%! Food for thought.

Anyway, if someone can provide the spring rates and free lengths of the stock and an aftermarket spring, that would be great.

Yondering
01-09-2012, 23:24
OK, I won't quote all of the above, but can answer some of it.

First off, re. my comments about the 24 lb ISMI spring, it looks like they just sent me the wrong one; I'm sending it back to Lone Wolf tomorrow. Before installation, it's free length was a lot longer than the 17 lb spring I removed from the LW guide rod assembly, but after shooting it, it's only about 1 inch longer. Hmmm, it took a set pretty fast. Anyway, I'll hold off any further conjecture about heavier springs until I get a replacement. I have a good assortment of 1911 springs, but got away from Glocks for a long time so I don't have very many Glock springs at the moment.

Your initial force of 9 lb is in the ballpark. The three 17 lb springs I have (OEM, ISMI, and unknown round wire) have 6-8 lb initial force. I measured my G21 last night, spring length was 3.132" slide closed, and 1.128" slide fully open. This "fully open" length is just before coil bind with the 17 lb springs, I have a dual spring setup, like a Sprinco but some other brand, that hits coil bind before this point.

I have to post my spring plot and rates tomorrow, but for now, at the 3.132" and 1.128" dimensions, my 17 lb springs are linear between 8 lb and 17 lb, or 7 lb and 16 lb, etc, depending how used they are, so the rate is roughly 5 lb/in, or a little less.

tlrgsxr
01-10-2012, 04:35
Good to hear. Your measurements are ideal! The important part is knowing the working range of the springs. We don't really care about the free length anyway, it's only useful for making calculations when the working loads are difficult to measure. Plus, the free length can vary a lot and that can throw of calculations. Looking forward to your results and the info for the aftermarket spring!

nickE10mm
01-10-2012, 06:08
Thanks, guys... this is a really great discussion here.... can't wait for some numbers. As I've said, I'll try and get some range data... and someone else can provide the math numbers. :)

gofastman
01-10-2012, 17:34
can anyone explain why these swampfox 200gr XTP's@1240fps did this with my 6" lone wolf barrel and 20lb ISMI spring:
http://www.thehighroad.org/attachment.php?attachmentid=140617&d=1303075740

but had no bulges or pressure signs out of the OEM barrel?

Yondering
01-10-2012, 22:50
I'm not a member of THR, so the link doesn't work for me. Can you post the picture here?

Assuming you got some sort of pressure signs, the first thing that comes to mind is the tighter chamber and throat dimensions in the LW barrel. The glock chambers are "generous", and the throat dimensions seem to be just about right, with a real smooth slick finish. Either a tighter chamber, or tighter throat, or rough finish will cause higher pressure; the LW barrels seem to have all of the above (OK, I've only had 2 LW barrels, but both are very tight, and rougher finish than Glock barrels) IMO, LW barrels have tighter chamber dimensions than necessary for good accuracy.

gofastman
01-11-2012, 16:34
fix't

Any Cal.
01-11-2012, 17:10
You might put a caliper on the case head and get the minimum and maximum size of the case head, if possible. One measurement across the blown out portion, and one measurement across the supported portion.

Do you have chrono #s for the round in both guns?

Any Cal.
02-10-2012, 01:18
OK, I think this sort of illustrates the point of where pressure is the highest... Off another forum...

http://intruder.0nyx.com/1.jpg

http://intruder.0nyx.com/3.jpg

Not my pics, came across these elsewhere, referenced on a couple other forums.

-Edit- it is possible the cylinder has been rotated, which then wouldn't be showing much of anything. Leaving the pics up anyway, just 'cause they are interesting.

robert91922
02-10-2012, 04:18
double post :embarassed:
sorry

robert91922
02-10-2012, 04:28
can anyone explain why these swampfox 200gr XTP's@1240fps did this with my 6" lone wolf barrel and 20lb ISMI spring. But had no bulges or pressure signs out of the OEM barrel?
Send this LW barrel back. Such lack of case support is unacceptable for aftermarket barrel. This brass doesn't have glock smileys, better said these are wolf bellies. IMO it's close to KB!
Certainly not ammo issue.

gofastman
02-10-2012, 15:53
Send this LW barrel back. Such lack of case support is unacceptable for aftermarket barrel. This brass doesn't have glock smileys, better said these are wolf bellies. IMO it's close to KB!
Certainly not ammo issue.
That barrel is long gone, i sold it even before hearing all this business about late model LWD being unsupported

_The_Shadow
02-10-2012, 16:44
can anyone explain why these swampfox 200gr XTP's@1240fps did this with my 6" lone wolf barrel and 20lb ISMI spring:
but had no bulges or pressure signs out of the OEM barrel?

The recoil spring and or locking surfaces didn't hold long enough for the impulse/duration of the pressure spike, therefore the slide and barrel moved and then unlocked while pressure was still elevated. :wow:

Here is why I say this, if the slide and barrel are locked the primer doesn't have enough room to pop out intact and casing maintains it best support. But if unlock occurs then the primer can push its way out. Also if the slide is unlocked then the casing can be pulled rearward increasing the portion which is unsuppored and as the casing is being ballooned outward it to can work to push the casing even further outward. :shocked:

The only way to visually see this, is to video this with ultra high speed camera, so that the slow motion play back can record the event.

_The_Shadow
02-10-2012, 16:53
gofastman, if you had the barrel and casings you could slide them back in the chamber to see if they still headspace or if they were pulled backwards increasing the unsupported condition. This would be evidence of lock up performance or lack of support.

Placing the spent casing back in the chamber, if it goes all the way into the chamber to be properly headspaced (case even with the barrel hood) that barrel would be lacking support.

But placing the casing back in the chamber and it stops short of full chambering (case sticking above the barrel hood) then the deformity exceeds the chamber's original headspacing, this shows it slid back out while the impulse was in progress showing signs of early unlocking!

nickE10mm
02-10-2012, 20:08
gofastman, if you had the barrel and casings you could slide them back in the chamber to see if they still headspace or if they were pulled backwards increasing the unsupported condition. This would be evidence of lock up performance or lack of support.

Placing the spent casing back in the chamber, if it goes all the way into the chamber to be properly headspaced (case even with the barrel hood) that barrel would be lacking support.

But placing the casing back in the chamber and it stops short of full chambering (case sticking above the barrel hood) then the deformity exceeds the chamber's original headspacing, this shows it slid back out while the impulse was in progress showing signs of early unlocking!

I agree 100% with this idea. :cool: