It looks like something to seat percussion caps on revolver nipples instead of using a wood dowel?
Dave, that's a thinga-ma-bob.
I acquired 4 of these things last week and don't have a clue what they are for. They are brass, about 2 1/2" long. I thought they might be some kind of capping device. The inside diameter of the outer tube is slightly larger than a #11 cap so it will not hold a cap snuggly. The outer tube slides back and forth about 1/8". Any Ideas? David