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Old 03-23-2011, 09:11   #1
dkf
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.357sig Pressure vs Setback

Don't know if its been posted before but..... I found a nice graph showing how bullet setback effects case pressures on the .357sig Speer GD 53918. Thought it was interesting.

http://le.atk.com/pdf/357_SIG_Setbac...s-Pressure.pdf
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Old 03-23-2011, 12:11   #2
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That's a very informative graph, thanks for sharing.

Bob
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Old 03-23-2011, 12:58   #3
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Interesting, I never know that at some point the powder compresses and pressure actually decreases because it doesn't all ignite. Although granted it's a small decrease.

Is this chart available for any other calibers?
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Old 03-23-2011, 13:14   #4
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Interesting, I never know that at some point the powder compresses and pressure actually decreases because it doesn't all ignite. Although granted it's a small decrease.

Is this chart available for any other calibers?
That anomaly would vary from caliber to caliber & w/ diff powders. The graph would NOT be the same for say 9mm, 40 or 45acp.
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Old 03-23-2011, 18:51   #5
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What's interesting is that at no time does the pressure exceed proof levels. That kind of puts a damper on the whole setback causing KB theory.
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Old 03-23-2011, 19:36   #6
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What's interesting is that at no time does the pressure exceed proof levels. That kind of puts a damper on the whole setback causing KB theory.
Again, caliber & powder specific. That is one graph for one caliber & one powder. Also keep in mnd @ 0.940", there is likely zero neck tension & the pressure is relieved some for that reason. You can clearly see signiicant pressure increases @ 1.040"-1.030". ENough for a KB, probably not, but 10K over pressure is not to be taken lightly, especially w/ handloaded brass fired maybe one time to many.
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Old 03-23-2011, 19:46   #7
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Again, caliber & powder specific. That is one graph for one caliber & one powder. Also keep in mnd @ 0.940", there is likely zero neck tension & the pressure is relieved some for that reason. You can clearly see signiicant pressure increases @ 1.040"-1.030". ENough for a KB, probably not, but 10K over pressure is not to be taken lightly, especially w/ handloaded brass fired maybe one time to many.
Agreed. I would like to see similar graphs of a particular caliber...cough! 40SW...cough! Also, I agree that setback isn't something to be desired. However, we hear so much about the dramatic pressure increase, and in this case the bullet is almost flush with the case mouth and the presure isn't high enough for catastrophic failure.
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Old 03-23-2011, 19:48   #8
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Agreed. I would like to see similar graphs of a particular caliber...cough! 40SW...cough! Also, I agree that setback isn't something to be desired. However, we hear so much about the dramatic pressure increase, and in this case the bullet is almost flush with the case mouth and the presure isn't high enough for catastrophic failure.
Again, loss of case neck tension causes incomplete combustion w/ slow powders used in the 357sig. I have seen this w/ H110 in magnums & little or no crimp, you'll get a hangfire or really low pressure event. I doubt that you would get sim results w/ say, my fav, TG in the 40 & 180gr bullets deep seated.
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Old 03-23-2011, 19:57   #9
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Again, loss of case neck tension causes incomplete combustion w/ slow powders used in the 357sig. I have seen this w/ H110 in magnums & little or no crimp, you'll get a hangfire or really low pressure event. I doubt that you would get sim results w/ say, my fav, TG in the 40 & 180gr bullets deep seated.
Yeah, but there is only so much energy in a given powder charge, no matter how you handle it. A light charge of fast powder has a limit as to how much pressure it can produce even in a completely cloased system (a "bullet" that doesn't even move). Id like to see a graph of 40SW with dramatically reduced OAL and a worst case scenario of a short OAL and a bullet that doesn't even move out of the way. Not that a graph like that is likely to pop up any time soon, but I wonder if the ballistics labs have run tests like that.
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Old 03-23-2011, 23:10   #10
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Yeah, but there is only so much energy in a given powder charge, no matter how you handle it. A light charge of fast powder has a limit as to how much pressure it can produce even in a completely cloased system (a "bullet" that doesn't even move). Id like to see a graph of 40SW with dramatically reduced OAL and a worst case scenario of a short OAL and a bullet that doesn't even move out of the way. Not that a graph like that is likely to pop up any time soon, but I wonder if the ballistics labs have run tests like that.
Well if I could just find a cheap 9mm & 40 bbl for my TC, then I would pop for the RSI pressure trace system.
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Old 03-24-2011, 08:50   #11
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Is this chart available for any other calibers?
I havn't found any for other calibers.

Found the chart here. There is some other interested info also.
http://le.atk.com/general/irl/technicalbulletins.aspx
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Old 03-24-2011, 16:16   #12
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The pressure issue with the 357Sig is interesting and bullet setback is something I check for all of the time. Has anyone heard of a KB caused by set back over-pressurization? Just wonder how often it is happening.
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Old 03-24-2011, 17:41   #13
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Fred:
I'm surprised you don't already have a full internal ballistics lab at this point. Maybe we should tell Jack everyone has one so he'll get one.

DFK:
Thanks for bringing this topic up.

PGH:
It's hard to tell how many KB's are due to setback. It all ends up being conjecture. All we really have is broken guns and burst cases. Maybe a lab could figure these things out, but these things rarely get that far. If and when they do, the results aren't made public, or at least I never get to see them.

My own personal conjecture is that KB's are due overwhelmingly to overcharged loads. This requires the admission of human error, which requires humility, which is rare.
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Old 03-24-2011, 19:26   #14
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Found some more articles.

My tests with Speer GD 23918 in my G33 did not concur with the article in the link below. After 3 chamberings the OAL went from 1.125" on a new bullet to 1.090" after being chambered 3 times. After two chamberings there was a minimum of .010" setback.

http://www.handguninfo.com/Archive/w...back.chart.htm

Found some .40 articles also.

http://www.greent.com/40Page/ammo/40/180gr.htm

^ Notice the massive pressure spikes of the .40 with bullet setback. Those numbers seem almost too high to be true. But if they are true I can see why a KB could happen.

http://www.thegunzone.com/glock/setback.html

Last edited by dkf; 03-24-2011 at 19:28..
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Old 03-24-2011, 19:42   #15
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Originally Posted by dkf View Post
Found some more articles.

My tests with Speer GD 23918 in my G33 did not concur with the article in the link below. After 3 chamberings the OAL went from 1.125" on a new bullet to 1.090" after being chambered 3 times. After two chamberings there was a minimum of .010" setback.

http://www.handguninfo.com/Archive/w...back.chart.htm

Found some .40 articles also.

http://www.greent.com/40Page/ammo/40/180gr.htm

^ Notice the massive pressure spikes of the .40 with bullet setback. Those numbers seem almost too high to be true. But if they are true I can see why a KB could happen.

http://www.thegunzone.com/glock/setback.html
Regarding the second two links, I don't put any faith in them. One has been shown to have manipulated his "evidence", or refused to admit it was eroneous, and the other I have met personally on several occasions and he is a buffoon and a braggard.
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