shouldn't the bullet have been deeper in the tree since the war was 150 + years ago when the bullet was fired that hit that tree, and the tree grows from the outside 1 inch or so which makes the rings ever expanding? I've cut down my fair share of old oaks and one 150 + years old would be a bit larger around than that one. Just an observation!
Did they have bullets made of some sort of ceramic or stone like material?