Wild guess, but from your hints, I'll say it is a separated shell extractor tool inside an outer sleeve.

A tompion is a good guess, but a tompion has a shoulder or taper to keep it from falling down the barrel.

I liked Tom C's entry for a rolling pin for a one armed baker though.

What do you say to a one legged hitch-hiker? Hop in!

Voting for anti-gun Democrats is dumber than giving treats to a dog that shits on a Persian Rug