I've started cleaning brass and have come across a number of cases with these indentations on them. They go all the way around, the depths of the indentations vary as they go around. They also vary from case to case. So far about 4-5 out of the dozen or so I've pulled out of the tumbler have them.

Running them through the de-priming/resizing die has little to no effect. At first I thought they were from the die, but then I realized they were like this coming out of the tumbler.

I do not know which pistol they came from, or even if they came from one of mine for that matter. I had previously gathered some cases from an indoor range that I know were not mine; those were mixed in with mine. The head stamp does match mine, but that is not 100% conclusive.

Thoughts on what could cause it? Is this a concern? Both from the aspect of if they are from my gun as well as should I reload them?

 

That is a ring crimp to hold the bullet in the casing. Seems kinda low on the brass. I would toss them.  There was some WWII surplus

ammo with a crimp like that from 1942.  What are the head stamp markings on those? Post a pic of the head stamp.

One thing for sure, you did not do that crimp. That looks commercially done.

I was thinking it could've been bullet crimp, but agreed it seemed low. 

Head stamp is F C - 9MM - LUGER

FC is Federal Cartridge the crimp could be to stop the bottom of the bullet from going past the ring.

America’s ‘New’ Favorite — 9mm Luger By Gun Digest Editors  June 22, 2018

Found this. pic from above article

Great find!

Should be fine to reload then, right?

 

Thats a pretty hefty crimp, I would say safe to reload but keep an eye out for stress. As the casing body gets worked a few times the thinner crimps of the brass can start to let go.

I thought I recalled a thread!! 

 

I see those from time to time in my range brass.

I clean and reload them like the rest with no issues.

Johnny B hit it - just a cannelure to prevent the bullet from being pushed farther into the case, thus increasing pressure. Happens with rounds that are chambered multiple times. Perfectly safe to reload.

Adios,

Pizza Bob