.40cal and Glock KB Thoughts

[ColdMan]

Ok,

I know the issue of .40S&W KB's have been beaten to death. I was thinking about this the other day, especially concerning Glocks in .40 and here is what I was thinking.

If a particular individual round (say round 24 of a 50 round box) is going to KB in a firearm due to (state reason here), what would you want to happen?

Knowing that force typically goes the path of least resistance, having a less supported chamber seems like a good thing. With the increasing pressure in the round, the pressure is going to expand brass to the ends of the chamber. Assuming the bullet has not left the muzzel, that 6 o'clock gap would be a good place for the case to rupture. The resulting brass fragments and hot gas jet going down the magazine well. I've seen in 1911's where the fragments and gas has punctured and set off the next round in the magazine while the magazine is being forced out of the well. In this case the powder just burned out through the hole in the top of the brass

Now if you compare this to a fully supported environment. The pressure is essentially bottled, like a pipe bomb. This seems like it would exibit more force on the barrel itself. This would cause the metal of the barrel to rupture and the case to seperate and blow backwards. The main exits to the barrel are going to be forward with the bullet leaving, and aft with the shell (pieces) leaving.

Now from my perspective, I do not want much of the force coming backwards towards my face, eyes and teeth. My doctor has assured me that most, if not all body parts do not grow back. (Mostly after I dislocated my arm, I asked him if we could amputate and let it grow back, he said no.)

Given that a major KB is going to tear the barrel open from chamber end and possible shots parts backward, would you want extra force vented down through the mag well? In either case the gun is destroyed.

Now the next question is that given a choice between a minor KB that might be seen as a case rupture in a Glock, or as being contained in the barrel with no case rupture and increased recoil, for example an HK where "That one felt weird"). Which would be preferred? The case rupture where the firearm is damaged a little, or the contained one that potentially weakens the chamber and barrel of the example HK, and could lead to more major damage later?

Do you think a Glock could survive multiple Minor KB's as a result of the chamber support being less than a more supported firearm that might rupture due to increased metal fatigue?

I was just thinking about this while working on an HPLC detector where the flow cell gasket had failed. My brain was on pressure mode.

[SDBettas]

For the record

[redskyzatknight]

My thoughts are www.doubletapammo.com is producing full power 40 ammo @ 6k under SAMMI specs. I'm ordering some today. I see no reason not to use this ammo exclusively for SD. Plus, I've shot 700 rds. of G-A "40+P+" through my stock Glock's with no problem.

[SDBettas]

So if there is some manufacturer who is labeling their .40 rounds as +P+, then they are making things up as they go. And since there is no SAAMI +P or +P+ rating for .40, who knows what pressure level they are loaded to.

[noway]

{So if there is some manufacturer who is labeling their .40 rounds as +P+, then they are making things up as they go. And since there is no SAAMI +P or +P+ rating for .40, who knows what pressure level they are loaded to.}


Which is more of a reason that makes the 40sw Kaboom such a mute issues or the glocks are so UNSAFE myth so over rated.

if somebody can shoot a so-called 40 +p+ load and get by doing it safely, then one can assume that commerical off the shelf loaded 40sw ammo built to a authority of SAAMI would be safe.

[redskyzatknight]

This 40 +p+ issue has been beat to death. www.georgia-arms.com markets +p and +p+ 40 ammo. I put +p+ in quotes like this: "+p+" for a reason though 35k has come up from an ammunition maker I trust who is also a mod here on GT. Either way, it's my opinion KB's are nothing to worry about with factory ammo that has'nt been chambered 100 times. If you fear KB's so bad shoot a crossbow.

[Tito]

Coldman:

Do you think it is possible that a very loose chamber could allow a cartridge to expand and rupture, thereby creating excessive pressure on the chamber wall and then causing chamber failure and the notorious KB?

[ColdMan]

Tito,

No, I'm thinking the opposite. The looser chamber would allow for more expansion of the brass, and a slightly less pressure. As the pressure builds the 6o'clock gap would act as a vent for excess pressure if/when the case ruptures. Reduced pressure means reduced forces and less of a Boom.

If anything, it seems like a looser chamber and more gap at 6 o'clock would reduce the chance of a severe KB that might destroy the pistol.

So in my thinking their are two main points to the glock's slightly looser than normal chamber.

First off. The chamber would increase the chance of a case rupture with a normal load due to whatever reason... Which would have to call a KB. But this typically does little damage to the firearm. This might be contained in another make of handgun.

Second. The looser chamber and bottom gap would allow for a vent for excessive pressure. This would and does rupture in most cases of a major KB. If anything, this would help vent a good amount of the pressure and serve to decrease the damage done to pistol/shooter by not allowing the pressure to build as high. In my mind, this is a good thing. If a gun is going to explode on me, I would rather it be at a lower pressure. It seems that the glock design would allow for part failure at a lower pressure which would prevent a more extreme boom.

So in summary, having a firearm fail at a slightly lower pressure in the event of a KB would be more advantageous than allowing the pressure to build to a higher point before firearm failure. While this might increase the chance of a case rupture, if would decrease the risk of injury in the event of a high pressure KB. This is assuming that the High Pressure KB has enough force to KB any firearm.

The counter arguement is that you have an event that does not exceed the failure point on another firearm, but does allow for a KB in a glock. This is referring to the case ruptureing and hot gas and brass shards go cutting through the frame. While some might argue that this is not a KB, I would say it is. Another firearm may be able to contain this, but the force of this event will be absorbed by the firearm. This could cause increased fatigue on the metal parts, which could allow for a decreased failure pressure for subsequent loads. Where the glock might retrain its barrel and chamber failure point, while having reduced frame life.

[philkryder]

I agree with your thesis.

Just opinion, but I think that the unsupported chamber is a safety feature. A pressure releif valve for cartridges.


It would be interesting to see a test run with identical Glocks (or maybe 10 of them) - Half with tight chambered, fully supported barrels and half with stock.

Then, fire successively hotter proof loads and observe...

I'd be interested to see:
1) which barrel had the higher pressure for a given level of powder in the proof loads.

2) which had case ruptures first and at what pressure

3) what proof levels it took to cause barrel failure or other physical damage to the pistols...


Phil

[ColdMan]

Exactly, a pressure release valve so to speak, or shear bolts made to break off at a particular force rating.

That would be an interesting test.

I think what would be really interesting would be to try to order some non-chambered .40S&W barrels from glock or other manufacture, so that in theory we have barrels made from the same stock material.

Cut several of these with the standard glock chamber, and cut the others with tighter more supported chambers. Then measure failure pressures.

Then as mentioned, maybe run each set to failure starting with max loads and working up. Try one set to failure with 120% max loads, another with 140. 160, 180, 200, and so on. Measure failure both with case and barrel failure.

One of the points I would be interested in, is that if a series of rounds that cause repeated case ruptures in the Glock Factory Chamber and no rupture in the more supported barrel, which barrel would fail first?

Odds are we would trash a few pistols trying this. But the data acquired would be worth it.

[noway]

I'm pretty sure glock has already done this type of testing.;)

You might want to look at clarks attempts with overloaded 40sw. You will find that what he has done and the type of failures that develop, should calm down most if not all of the KaBooms theory/myths and false rumors.