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Old January 8, 2020, 11:22 PM   #62
Join Date: February 12, 2001
Location: DFW Area
Posts: 22,958
Do they set back or is it limited only to the first round chambered? Should not this set back be happening to all the rounds cycled through the gun?
No, it isn’t limited to the first round chambered; it happens to any round that is chambered enough times for the bullet to be set back. It’s important to understand that it’s rare for a bullet to setback from only one chambering/loading unless there’s a problem with the gun or the round. However, it’s not that uncommon for a round to setback if it is chambered repeatedly.

The reason it most often happens to the first round (or first two rounds) in the mag is that if a person is constantly unloading and reloading, it’s only the top round (or top two rounds) that get chambered repeatedly.

The chambered round is ejected during unloading. If the person doesn’t top off the mag when loading then the ejected round is put back into the magazine for the next time the gun is loaded and it gets chambered repeatedly until it is shot or replaced. In that case, only the first round is getting chambered frequently and therefore it’s the only one that is likely to show setback.

If the person tops off the mag (full mag and one in the chamber), then the easiest reloading method is to chamber the next round in the mag, remove the mag, put the ejected round back in the mag and the put the mag back in the gun. So the top two rounds will get “rotated” each unload/reload cycle until shot or replaced. Each of the top two rounds would be chambered once for every two unload/reload cycles.
Some of the photos here are dubious. Not all but some look cooked.
Sadly, given the way this discussion has progressed, I anticipated such accusations would be made. That’s why in addition to taking and posting two pictures of my own, I also went to the additional trouble of finding a third party article on the web that had a picture showing the same thing as my photos did. There are other similar photos available on the web if one does an image search.
There is still the issue of there being no firearm or cartridge manufacturer with a warning about set back.
Glock mentions the issue in their armorer’s manuals and includes the following warning—reproduced below from a 2015 edition with the emphasis present in the manual:
Originally Posted by 2015 Glock Armorer's Manual
“Set Back”

Cartridges sometimes may be damaged or altered in some way and this can cause an unsafe condition. An example is a cartridge that has had the projectile (bullet) pushed back deeper than normal into the casing. This can change the combustion space characteristics and powder burn rate boosting pressures to unacceptable levels. Repeated loading and unloading of the same cartridge can cause a condition known as “set back.” The projectile has been pushed deeper into the case and the overall length of the round is noticeably shorter than others of the same bullet weight, make or style.

For what it’s worth, the topic is also commonly addressed in reloading manuals.
Do you know about the TEXAS State Rifle Association?
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