Marks on 9mm range brass

I do pick up range brass. It's interesting. Someone left one piece of Starline 44 Special. I pick up and sort out 9mm brass to reload, other calibers go in the recycle bucket. I've got one of those rotary tumbler cleaners with water and steel pins. When the brass comes out it's as clean as brand new. I can't see not using range brass. At least for 9mm and just general plinking.

But what caused the line on these cases? It's some sort of indentation that goes all the way around. It's deep enough to catch on your fingernail. It must be from the same gun since it's in the same location on each case. (Not my gun or my cases. I won't be using them either.)

Any guesses?

That is a type of crimp to prevent a bullet being driven farther into the case when chambering. Not seen as often as in the old days, it helps overcome the difficulties of obtaining a firm crimp in cartridges that headspace on the case mouth.

Oh, ok. That makes sense. I bet someone had some old ammo they were shooting.
Thanks,

"Cannelure", mainly to keep bullet "set back" from happening. Also I believe some cannelures were installed as a means of identification (some cannelures are way too far back from where the bullet base would be)...