Looks to me like a fired bullet impacted onto another piece of metal, which is probably another fired bullet. We civil war relic diggers occasionally find "Robin Hood" bullets. Name comes from Robin Hood splitting an archery contest opponent's arrow. A fired bullet impacts into a tree, and another bullet coincidentally lands in the hole made by the first bullet. It also happens in target-shooting, when a paper target is nailed onto a board. People sell the civil war ones as "collided" bullets, but they are NOT a mid-air collision. If they'd met in mid-air, they'd be stuck together nose-to-nose.
The photo below shows theresult of two fired bullets meeting in mid-air. It also shows the the "outward-spreading" of the bullet's body-rings, which I think is what I see on the lead object you found.
Please measure and tell us the diameter of the flat end of the circular projection. Its diamter can either confirm or exclude that part of the object as being a bullet.