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#1
02-22-2017, 12:13 PM
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Bullet Setback
I was having a discussion about condition 1,2 and 3 carry and the subject of bullet setback came up. For those who have been carrying concealed for a long time, this will be "old stuff," but it struck me that there are "newbies" out here that don't know what bullet setback is. So... I'm going to post three pictures (forgive me, the quality isn't that good, but you can see what's happening).
First, what is "setback?" When you load a round into a semi auto pistol, there is stress place on the bullet itself. Most people, if they unload their firearm, will pull their magazine, then eject the round in the chamber... THEN put that ejected round back into the magazine. Next loading... they put the same round in the chamber. Setback occurs with repeated loading, pushing the bullet further back into the cartridge. The pictures show a normal Sig Sauer 38 Super JHP with an overall length of 1.240 inches, flanking a setback round.  The second picture shows a caliper still set at 1.240, but with MY first round off the top of the magazine. That bullet has been setback in the cartridge to an overall length of 1.177. You can see the physical gap between the bullet nose and the caliper.  Is there a problem? Yes, there is. Compressing the bullet further than recommended will cause increased pressures that can create an unsafe condition if fired. Old timers call it a "kaboom". At minimum, the round may just fire as a very hot load, at its worst, you may find yourself at the local hospital having your grips removed from whats left of your hand. Just a reminder... check your ammo for overall length from timer to time, and be aware. I've been shooting for most of my life and I forget the simple stuff from time to time. Now... how many people are going to line up their carry ammo and look at it when they get home?
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COTEP: CBOB578 DW CCO SIG GSR 1911 SA Micro Compact and a spectacular cast of others! "You have never lived, until you have almost died. And for those who fight for it, life has a flavor that the protected will never know." Guy de Maupassant, 1893. Anonymously, penned on a sign at a command post at Khe Sanh, RVN. 
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#3
02-22-2017, 12:27 PM
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Ya know
 , it was the conversation between you and  that touched off my thought process about setback. So I went to my EDC , ejected the chambered round and didn't even need to use a caliper. Startled me a bit... I'm sure my Guardian would have handled the pressures, BUT... we can't be too careful!
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COTEP: CBOB578 DW CCO SIG GSR 1911 SA Micro Compact and a spectacular cast of others! "You have never lived, until you have almost died. And for those who fight for it, life has a flavor that the protected will never know." Guy de Maupassant, 1893. Anonymously, penned on a sign at a command post at Khe Sanh, RVN.
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#4
02-22-2017, 12:46 PM
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Yes, this can be dangerous in a gun if its bad enough. I had this issue as well with my 10mm. While chronographing some loads I was getting very inconsistent numbers. I found than some loads were "deeper" than other causing issues. Careful reloading with proper crimping on straight walled bullets can help but attention to detail is important.
Well said Padre!!
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