powder charge versus velocity, always linear? [Archive] - Glock Talk

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Andrew Tacquard
06-10-2014, 13:34
Tried posting this yesterday, guess it was deleted.

I noticed that my powder charge versus velocity plots were somewhat linear with my bullseye loads. I was loading to make major, and worked up a load to about 168 PF. So when I was making my subsonic 300 BLK loads I made three loads (that I knew were well within the safe region), plotted them, fit a line, plugged in the desired velocity to my equation and it spit out a charge. I loaded to the charge and I was within a few fps (equation was correct). I am trying the same thing with WST for my new pistol loads, again loading major. I made two loads this time (and assumed a linear relationship), got the data, made an equation and loaded rounds based on that. I have not chronoed those loads yet, but I suspect they'll be darn close.

Is powder charge versus velocity mostly linear when your staying away from max charges? I know most everything in nature is non-linear and I suspect at the low end and high end it will be non-linear as well. However, if this holds up it sure makes my work up process faster and easier when I loading to a velocity.

WeeWilly
06-10-2014, 13:53
In my experience it is not always linear. I think the conclusion that it is somewhat linear is more a function of how small a part of the pressure curve you are inspecting/measuring, than anything hard and fast.

Colorado4Wheel
06-10-2014, 15:21
In the middle part I have found it to be somewhat linear.

fredj338
06-10-2014, 16:18
My exp, it depends. For most powders, as C4W notes, vel will be linear in the midrange. With faster powders, the pressure curve steepens as you get closer to max, vel can also go up OR they can flatten. If you are adding powder & getting no appreciable increase in vel, it could mean you have reach working max for that powder. Trying to make major for what caliber? IMO, not really safe with fast & uberfast powders, you run the risk of a pressure spike as you near the top end.

Andrew Tacquard
06-10-2014, 16:54
Trying to make major for what caliber? IMO, not really safe with fast & uberfast powders, you run the risk of a pressure spike as you near the top end.

10mm.

jmorris
06-10-2014, 19:04
It will never be linear. At some point above 0.0 grains the bullet will leave the barrel and at some point over max it will remain in the barrel as the rest of the gun explodes.

A good rule of thumb reloading is to never speculate. Test, test and test, then record you data (and post it).

mboylan
06-10-2014, 19:50
Fast powders are often very non-linear close to and over the max.

fredj338
06-10-2014, 21:34
10mm.

Few powders faster than w231 are safe for 10mm max performance loads. Lets call that 180gr bullets @ 1200fps. High pressure rds run that way, need powders slower than w231.

WeeWilly
06-10-2014, 22:16
Tried posting this yesterday, guess it was deleted.

I noticed that my powder charge versus velocity plots were somewhat linear with my bullseye loads. I was loading to make major, and worked up a load to about 168 PF. So when I was making my subsonic 300 BLK loads I made three loads (that I knew were well within the safe region), plotted them, fit a line, plugged in the desired velocity to my equation and it spit out a charge. I loaded to the charge and I was within a few fps (equation was correct). I am trying the same thing with WST for my new pistol loads, again loading major. I made two loads this time (and assumed a linear relationship), got the data, made an equation and loaded rounds based on that. I have not chronoed those loads yet, but I suspect they'll be darn close.

Is powder charge versus velocity mostly linear when your staying away from max charges? I know most everything in nature is non-linear and I suspect at the low end and high end it will be non-linear as well. However, if this holds up it sure makes my work up process faster and easier when I loading to a velocity.

So my guess in the pool is your WST loads will end up +.2gr over your Bullseye major load, everything else being equal (including OAT),

Colorado4Wheel
06-11-2014, 10:57
Since we are talking 10mm. The stock G20 will start opening too fast around 1150fps with a 180gr bullet. So you get erratic ES/SD as a result. A heavier spring will solve this problem. To me your driving the gun past what it is designed to do at that point. But most people think the 10mm is actually a MAGNUM so they just throw a heavier spring in and up the charge but another 10%. A heavier spring will setttle the ES down and let your shoot loads that are easier to understand over the chrono because they are not as erratic.

WeeWilly
06-11-2014, 12:01
I must have missed something, which certainly will not be the first time, but by my estimate you need about 920fps with a 180gr bullet to make major. Call it 950fps for a margin for error. That should be pretty easy with WST and 10mm.

fredj338
06-11-2014, 13:23
I must have missed something, which certainly will not be the first time, but by my estimate you need about 920fps with a 180gr bullet to make major. Call it 950fps for a margin for error. That should be pretty easy with WST and 10mm.

Or any of the powders available. The definition of major needs to be qualified though.:dunno:

WeeWilly
06-11-2014, 13:29
Or any of the powders available. The definition of major needs to be qualified though.:dunno:

I was assuming the OP's meaning of Major was 165pf, perhaps that is where I missed the boat.

Andrew Tacquard
06-11-2014, 14:21
I was assuming the OP's meaning of Major was 165pf, perhaps that is where I missed the boat.
WeeWilly your the only one on the boat with me...

Sorry I assumed everyone knew what major PF meant, I figured by including my goal of 168 that would narrow it down. That explains all the concerns for over pressure, running to fast, fast powder, etc. So from the current USPSA rule book "Power factor is calculated using the bullet weight and the average velocity of the three rounds fired, according to the following formula:
Power Factor = bullet weight (grains) x average velocity (feet per second) / 1000". I am running 200 grain lead (and next is coated bayou bullets), I need 825 fps to make "Major"; which from the USPSA rule book is 165 (using the above formula). I settled on 168 as it gives me some margin for weather changes or slow chronos. 168 requires a 200 grain bullet to be moving 840 fps.

Andrew Tacquard
06-11-2014, 14:26
It will never be linear. At some point above 0.0 grains the bullet will leave the barrel and at some point over max it will remain in the barrel as the rest of the gun explodes.

A good rule of thumb reloading is to never speculate. Test, test and test, then record you data (and post it).

I am not speculating, I am collecting data via a quasi scientific method, analyzing it, fitting a curve (in this case a line), and drawing conclusions from my results. Then I verify my results with further testing, pretty much the standard process for developing anything. Since I have been looking at the data, it has been dang near linear in the area I've been testing. R^2 values of .95 and .97. I realize at the ends it is non-linear; however I am no where near 0.0 or max loads.

Andrew Tacquard
06-11-2014, 14:28
also, Fred, Willy and Steve you all recommended I use the WST with light lead loads. http://www.glocktalk.com/forums/showthread.php?t=1516370

Andrew Tacquard
06-11-2014, 14:29
So my guess in the pool is your WST loads will end up +.2gr over your Bullseye major load, everything else being equal (including OAT),

almost, 4.6 BE and 4.7 of WST, still need to chrono to verify.

WeeWilly
06-11-2014, 16:46
almost, 4.6 BE and 4.7 of WST, still need to chrono to verify.

Sounds like it should be very close.

Fred was the first person I read to point out the reverse temp sensitivity of WST. I shoot where the temps are very consistent and mild, so I don't have to worry about it, but as the temps go up as the summer wears on, your numbers may change. Maybe build in a little additional margin, you probably have some headroom if needed.

Andrew Tacquard
06-11-2014, 17:11
Sounds like it should be very close.

Fred was the first person I read to point out the reverse temp sensitivity of WST. I shoot where the temps are very consistent and mild, so I don't have to worry about it, but as the temps go up as the summer wears on, your numbers may change. Maybe build in a little additional margin, you probably have some headroom if needed.


So as it gets cold velocity will decrease? I chronoed today, wife is on the computer so I don't have the data yet. I did not have as much margin as I wanted, but I did it with my 29. As soon as I get another pistol for my daughter to shoot I'll be back to my 20 for matches and that'll put me well in the safe zone. I think I had an extra 20 or so fps with it.

fredj338
06-11-2014, 17:17
So as it gets cold velocity will decrease? I chronoed today, wife is on the computer so I don't have the data yet. I did not have as much margin as I wanted, but I did it with my 29. As soon as I get another pistol for my daughter to shoot I'll be back to my 20 for matches and that'll put me well in the safe zone. I think I had an extra 20 or so fps with it.

No, most powders are temp sensitive, losing vel & reducing pressures as it gets colder or increasing pressures & vel as it gets warmer. WST & probably a few more, are reverse temps sensitive. Meaning as the temps go up the pressures reduce slightly as does the vel. Read my blog on some testing I did.
For making PF, IDPA or USPSA, build in a little margin. Everything affects vel/pressures; temps, altitude, even humidity, so if you are right at min, then you are risking a DQ. I run major @ 170PF +/-. That way I know I am good regardless of sea level or 6K ft, 40deg or 110deg.

Andrew Tacquard
06-11-2014, 18:04
Thanks Fred, luckily with the 20 the PF is right at 170; the 29 was 166. So an excuse to hurry up and buy my daughter a pistol to use so I can go to my 20. So I ran the data. WST in the range I was loading was as close to linear as I think it possible, given all the variables. Predicted velocity was 832, average velocity for a string of 9 was 829; I was off by 3 fps on my guess using the data from the previous two loads. For some reason I loaded to 4.7 to make a power factor of 166; when I was wanting to get to 168. Which is the power factor I was running with bullseye. According to the data 4.8 grains would have got me to 168, so Willy was correct, 0.2 more grains than BE. I was testing bayou bullets and some regular lead from Missouri bullets. The R^2 value for the BB was .9974 and for MO .9968; again dang near a straight line. What is surprising was the lead bullets were about 30 fps faster. I didn't think coating would slow the bullets that much.

fredj338
06-11-2014, 18:19
Thanks Fred, luckily with the 20 the PF is right at 170; the 29 was 166. So an excuse to hurry up and buy my daughter a pistol to use so I can go to my 20. So I ran the data. WST in the range I was loading was as close to linear as I think it possible, given all the variables. Predicted velocity was 832, average velocity for a string of 9 was 829; I was off by 3 fps on my guess using the data from the previous two loads. For some reason I loaded to 4.7 to make a power factor of 166; when I was wanting to get to 168. Which is the power factor I was running with bullseye. According to the data 4.8 grains would have got me to 168, so Willy was correct, 0.2 more grains than BE. I was testing bayou bullets and some regular lead from Missouri bullets. The R^2 value for the BB was .9974 and for MO .9968; again dang near a straight line. What is surprising was the lead bullets were about 30 fps faster. I didn't think coating would slow the bullets that much.

I don't know about USPSA, but IDPA, PF is verified in the longest bbl pistol available. So if you shoot a 4" gun, you can test your ammo in a 5" gun. The bigger matches will have 5" guns around for testing.
The slicker you make a bullet, the less pressure, the less vel. I have NEVER fired a moly coated bullet that was faster than an uncoated one, rifle or handgun. Then lead bullets will often produce higher vel with the same charge as jacketed, why we are warned to not use jacketed data for lead. My theory, the slightly larger & softer bullet seals the bore better, increasing pressures a bit & giving higher vel. Until I get a pressure system, that is what I believe. Slicker bullets go slower, that I can verify by chrono. That tells me pressures are less.

Andrew Tacquard
06-11-2014, 19:04
I don't know about USPSA, but IDPA, PF is verified in the longest bbl pistol available. So if you shoot a 4" gun, you can test your ammo in a 5" gun. The bigger matches will have 5" guns around for testing.
The slicker you make a bullet, the less pressure, the less vel. I have NEVER fired a moly coated bullet that was faster than an uncoated one, rifle or handgun. Then lead bullets will often produce higher vel with the same charge as jacketed, why we are warned to not use jacketed data for lead. My theory, the slightly larger & softer bullet seals the bore better, increasing pressures a bit & giving higher vel. Until I get a pressure system, that is what I believe. Slicker bullets go slower, that I can verify by chrono. That tells me pressures are less.

Last match they used my gun to verify, I'll have to look at the rule book. I remember reading that they use the 5" barrel, but might have been IDPA. I knew lead was faster than jacketed; but was surprised the moly was that much slower. I think it is probably the sealing of lead is better, like you say.

jmorris
06-11-2014, 19:55
Idpa is a legal for division gun, USPSA is the gun you are using.

DanaT
06-15-2014, 07:45
I am not speculating, I am collecting data via a quasi scientific method, analyzing it, fitting a curve (in this case a line), and drawing conclusions from my results. Then I verify my results with further testing, pretty much the standard process for developing anything. Since I have been looking at the data, it has been dang near linear in the area I've been testing. R^2 values of .95 and .97. I realize at the ends it is non-linear; however I am no where near 0.0 or max loads.

Are you using single data points for each charge, or multiple data points for each charge.

Andrew Tacquard
06-17-2014, 19:16
Are you using single data points for each charge, or multiple data points for each charge.

I am using the average velocity of 10 shots at each charge.

DanaT
06-17-2014, 20:57
I am using the average velocity of 10 shots at each charge.

Dont use the average. Plot all points and then do regression analysis. It is more accurate especially when trying to determine linearity. You start seeing if you get more spread in the data at extremes.

If you want to get really fancy, check each group of 10 shots and see if they are normally distributed. When distributions change to non-normal you are probably getting into a non-linear region.

But your way is "good enough" for almost all calculations, its really only if you want to start seeing trends that the methods help.

jmorris
06-17-2014, 21:57
I realize at the ends it is non-linear; however I am no where near 0.0 or max loads.

The title had "always" in it, your never going to get that. However, if you narrow the scope of your data collection, it can look linear.

Kind of like the growth of a human. At 2-3 years you would have a different height gain per month than at 50-51 years off age but both would seem linear on a graph, within the one year sample point. When you look at all the data in between it would be a different story.

Andrew Tacquard
06-18-2014, 17:23
Dont use the average. Plot all points and then do regression analysis. It is more accurate especially when trying to determine linearity. You start seeing if you get more spread in the data at extremes.

If you want to get really fancy, check each group of 10 shots and see if they are normally distributed. When distributions change to non-normal you are probably getting into a non-linear region.

But your way is "good enough" for almost all calculations, its really only if you want to start seeing trends that the methods help.

concur, for the amount of effort I put in and the results I obtained it is good enough. I am just using the data to get a predicted load and then verifying it, rather than continuously going up or down on the charge until I get where I want. What I like about it is after two loads I know what I need. I am using a lee disk, and the answer is never the exact size of the cavity. Thus I end up modifying the cavity to get to the charge. The method keeps the guess work out of it. I agree the other method would be more accurate.

Andrew Tacquard
06-18-2014, 17:25
The title had "always" in it, your never going to get that. However, if you narrow the scope of your data collection, it can look linear.

Kind of like the growth of a human. At 2-3 years you would have a different height gain per month than at 50-51 years off age but both would seem linear on a graph, within the one year sample point. When you look at all the data in between it would be a different story.


correct, bad choice of words in the title, nothing is always or absolute. perhaps..."powder charge versus velocity, linear trends in mid range loads"