Well, at least the education about the civil war musket/pistol percussion-capper device will remain even if I have to cancel my ID guess. The brass object posted by Ripcon has a small knob at the end of a long narrow rectangular slot, as we also see on the percussion-capper. But now that he has posted a "backview" photo, it looks like the knob connects to a stud which holds a long flat piece of brass on the back of the object. That doesn't match up with a percussion-capper. What will tell us yes or no is the fact that a percussion-capper consists mostly of a long square tunnel, whose "business end" is hollow/open on one side, like a roof gutter. (Look closely at that end in the photo of the percussion-capper.) Ripcon, is that end of your object hollow/open, or just a flat piece of metal?