Unknown object


I have no idea what it is, but it comes to me in a big box of old ammo and military junk. It is a cylinder about 1.5cm tall with a smooth semi-circular groove on the side, you see the groove at 12 o’clock. No markings of any kind.


Maybe it is some kind of gunsmith tool or dejamming tool if a gun has trouble ejecting a case? Just made all that up as I really have no clue :-)