Looks like one of those old-school minie balls. Walker might know a thing or two about them.
I feel special. I know what they are, and I know that when I saw the picture that's what I thought of, but I have no idea whether that's what it is.
I'll see if FableFreak can pop in here for this...
I had that thought, too.
Would a Minie ball have been used in England then or just America?
Yeps. A French guy named, predictably enough, Minié invented them. They were used all over the place because they let you reload a rifled musket as fast as an unrifled one. That little hollow place spread out and fit in the rifling when it fired.
They were invented (I don't know, so to Wikipedia) 1850ish. Maybe it's from the Crimean War?
Incidentally, that's really cool. Assuming it isn't some kind of random trash that happens to look like a minie ball. Where'd the whippersnapper find it?
EDIT: And even if it is a coincidence, that's a supremely weird coincidence so much that it's very cool itself.