What would cause this on cases?

[glockster157]

The cannelure crease below the bullet would serve no purpose on a revolver load. All the force in a revolve is trying to unseat the bullet pulling it out of the case. The feeding cycle of an auto pistol tries to shove the bullet deeper into the case. As to rings in the chambers either by accident or design is very unlikely as this would not leave an indentation into the brass but rather a swelling outward of the case. When that was pulled from the chamber it would leave a bright mark where the brass was drug across the still lip of any ring in the chamber.

[Guest FroggyOne2]

Ah ok.. got ya.. your saying that there is a inward crease made into the brass..

[Guest FroggyOne2]

if that is the case, then the only thing that i can think of at the moment is that there is a burr cut into the chamber.. that was caused by the reamer.. if it is a pistol.. i would be perplexed if it is a revolver.

[glockster157]

I really can't see that either. first there is no way to run a reamer into a chamber and leave metal in the middle. It just doesn't work that way. And I see no way to add a ring after the chamber was created...at least no reasonable way. Besides that, even if there were a raised ring in the chamber, it was slide across the brass from the middle of the case to the mouth as it was extracted leaving marks all the way to the mouth. Those rings have to have been put into the brass outside the chamber.

[glockster157]

And I will add they are in a very common place to keep the bullet from setting back. From the location I would say it was a lighter bullet, if that is a 45 case I would say a 185 grain bullet.

[Guest Lester Weevils]

Yeah dunno why case cannelures seem pretty common in for instance .357 rounds.

Maybe a crimp on the back end assists the front crimp in preventing the OAL from increasing under recoil? After all, with the majority of semiauto ammo they expect a crimp on the front of the case to keep it from setting back? Maybe a cannelure would be useful to avoid setback in a tube-fed lever gun? Or maybe some manufacturers add the cannelure to revolver ammo for no sane reason at all?

These are 9mm cases and the diameter below the line appears to have been fire-formed, "blown-out", to about a 0.006" bigger diameter than above the line. Maybe the lines could have been machined into the ammo before firing, but am pretty convinced that the pistol did it.

That is a good point that a raised ring in the middle of the chamber might be expected to polish the front part of the brass during extraction, so if it has something to do with chamber dimensions I guess it would be most likely the mouth of the chamber having been bored a little bigger than the part of the chamber near the rifling?

It is difficult to see in the picture, but to the naked eye the FC cases have noticeably flatter primers than the RP cases, though neither is absurdly flat. If they were hand-loads, wouldn't we have to assume that the fellow used softer federal primers in the FC brass and then switched to use harder primers in the RP brass? Such a thing would not be impossible, but it just seems unlikely?