I got this in a batch of CZ601 parts, but I just can't think this is a CZ part. I'm surely wrong about a lot of stuff, so this might be another case of that.

Steyr ?

Unsure. The hole at the rim seems a little odd, and I kinda remember seeing something like that before, but I'm really drawing a blank.

Looks like a 1917 Enfield extractor

J Wisner