The tip on your bullet looks like it's sporting ammo. I use 165 grain boat tail spire tips in my 30-06. Spire tip means the tip has a small amount of exposed lead. The M1 Garand military round was 150 grain full metal jacket with a flat base. I can't tell if there are rifling marks on the bullet. If there are, someone could have fired the rifle into the air, and you found the spent bullet. What goes up must come down, and some people are dumb enough to do that, not thinking where the bullet might land. A friend of ours was inside their upholstery shop, and a fellow deer hunting fired at a sky lined buck, missed, the bullet went over the hill, through the wall of the shop, and hit her just above the belt on her side. Didn't reach any vitals, but none the less, who wants to be hurt like that. The shooter got busted, and lost his hunting privileges among other things. If no rifling marks are on the bullet, then someone that reloads his own might have dropped a bullet on his way into church.