.45 ACP Case Length

This topic was touched upon in an earlier post. By chance I pulled out an old "Shooting Sports USA" magazine from Sept 1991 (good periodicals, glad I kept mine.) It had published test results by Hugh Birnbaum on measuring 45 ACP case lengths. Min spec case length is theoretically 0.888, and max is 0.898. He resized and measured hundreds of 3x fired Federal and once fired Sampson (IMI) cases. There were great variations in case lengths, and significant number of the Federal were well below 0.888.

I measured a box of 50 Federal 7x resized, and a box of 50 IMI Match 2x resized. The Federal averaged about 0.888 with about 2/3 from 0.883 to 0.887, w/longest at 0.892. The IMI averaged 0.890 with all above 0.888, and much better uniformity, but still with significant variation from 0.888 up to 0.895.

I then did some searches on the internet on this topic. Consensus from the internet and the referenced article seems to be that .45 ACP headspaces on the case mouth only in THEORY, and in reality cases probably are held in place by the extractor. Of the 3 instances I found where someone had measured their 1911 chambers, all were about 0.900.

Bottom line, nobody seemed to care too much about .45 ACP case length, nobody bothers to ever trim cases, and nobody worried bout having cases under the 0.888 length. I have yet to find any of my cases over 0.898, but will continue to check periodically. As mentioned in an earlier thread, .45 ACP cases seem to shrink with continued reloads. I once knew a skeet shooter who used very old 12ga brass cases, continually reloaded them never discarding any. Guess the .45 ACP cases are somewhat like that.

I did have some PMC cases in a recent lot where some primers would not seat fully, first ever that has happened. In my "research", some folks did express concerns about high primers in reloads, but I could not find any instances of "slam fire" documented. However, I share concern about high primers and will not tolerate that in reloads.

You have discovered what the military has know since the 1920's that the .45 acp is one of the very few cases that in reality shrinks each time it's used instead of getting longer. You never have to trim a .45 acp fired in a semi-auto. I don't know if that also is the case if fired in a revolver but would not be surprised if it also shrank in that too.

"You have discovered what the military has know since the 1920's that the .45 acp is one of the very few cases that in reality shrinks each time it's used instead of getting longer."

Actually, in measuring cases I have observed shrinking for some time, never took the time to see it documented like this. What I really discovered is that the 45 ACP doesnt in most instances "headspace" on the case mouth.

This is a 48 round group at 25 yards, offhand, on my Gong target. This was fired in a M1911. I pick up range brass, bought buckets of "once fired" military brass, have reloaded the brass an un known number of times, and never segregated the stuff by any classification, never trimmed it, and it shoots just fine.

A bullseye shooter might think different.

As for high primers, on another forum a gentleman stated he had a high primer go off in a revolver. Seems the cylinder recoil had enough force to push the primer against the recoil shield and ignite it.

This must be very, very rare. I have been able to find lots of slamfires in Garands, due to that free floating firing pin, but only one account of a slamfire in a handgun.

Though, I recall reading accounts of rounds going off in a M1911 if the pistol was dropped with a round in the chamber. Hard to believe, especially as the firing pin has a rebound spring, but enough people were hurt that now M1911's have firing pin blocks.

https://www.milsurps.com/images/impo...nds230LR-1.jpg

Anyone know how much the 40 cal and others are affected by case stretch? How many times they can be fired before case length is a concern?

"...headspaces on the case mouth only in THEORY..." There's no theory about it. The .45 ACP headspaces on the case mouth. However, the fact is that .45 cases don't seem to get longer, no matter what load or how many times a case is used. Few, if any, handgun cases do. .38/.357 cases don't either. .38/.357 cases loaded with target loads, literally, last forever. So do .45 cases. As daft as that sounds.

You'll have to enlighten me. If a case length is 0.882, and if the chamber length is 0.900, and the extractor engages and holds the case, how is the case headspacing on the case mouth?