Here's another "What am I"

[PJgunner]

Looks like a bullet designed to be paper patched and fired from what was called a slug gun. I'd estimate the caliber to be around 40 to 42 based in the accompanying ruler. There were several rifles of that type that were used by snipers on both sides during the War of Northern Agression. I forget which side did it, but one of them shot a general off his horse at supposedly one mile.
These slug gun, IIRC weighed in excess of 20 pounds and were very accurate at long range.
Paul B.