Any idea what this is ?

[Sudsy]

Came in a lot of assorted black powder stuff I recently picked up.
I've no idea

Tin of caps for perspective

 

[sheriff john]

Looks to be part of an old-time shotshell reloading kit although it's not exactly the same as others I've had. May be a stand-alone tool for cartridges/shotshells. "Claw" for placing around the base to extract, circle to possibly determine proper circumference, and the other end which looks to be a hook to remove partial casings lodged in the chamber. It is old. It is cool. Thanks for posting.

 

[longcruise]

Looks like a gizmo. I got no idea but I'm sure curious.

 

[Sam squanch]

I believe it’s to extract a swollen paper shotgun cartridge if it’s stuck. I once saw a switchblade knife with 2 slots cut in the guard, one for 12 gauge and one for 16 gauge, so I think it was a common problem.

 

[OLUT]

Came in a lot of assorted black powder stuff I recently picked up.
I've no idea

Tin of caps for perspective

As others have noted, it is a "ring shell extractor" for swollen or stuck shotgun shells. These were common in the early cartridge period. They are usually stamped with the appropriate gauge , like the "10" that is mounted on my 10 gauge brass shell. They came with different designs, including a hook like yours at a higher cost. On some, the ring actually could be screwed in to reseat primers while reloading the spent shell.. For example, in 1880 a basic ring like mine cost 50 cents. A note in the catalog also indicates for

shotgun shells,"The ring handle on these shell extractors is suitable as a gauge for sizing body of shell after loading"

 

[Sudsy]

Excellent !
Thank you

 

[TarponStalker]

That's a nice one

 

[Newly O’Brian]

The hook is for pulling out the paper hull in the event it separated from the metal base.

It happened in the early days of paper shotshells