Just off hand it looks like a fired 45-70 bullet, but to be sure we need measurements in the 1/1000's of an inch, like .458, and also if possible the
weight in grains. Welcome to T Net. Where are you located? I'm asking because it's an historic bullet most commonly used in the west. The 45-70
cartridge was used mostly during the Indian Wars of the 1870's, but it's still in use today by folks that shoot the old trap door rifles and carbines. There
are other bullets that are very close to the .45, like the .44, which is why an exact measurement is required for definite ID.