This seam to be happing more lately from the use of old unknown military ammo. I have had 3 different firearms brought to me like this with stuck bullet heads. 2 rifles an 1 pistol. All were from using very old surplus from an unknown source. These young guys have no idea how some of the ammo has been taken care of. They buy it at a gun show very cheap. One guy bought ammo that looked like it was tumbled clean. All there i was able to push out after sitting over night with the bore full oil. Then just tapped out with a brass rod of bore diameter.