Ruger precision rifle .223 caliber, had 50 rounds loaded with 24 gns Varget with 68 gn HPBT bullets. All fired perfectly except for one. That one sounded and felt the same as the others and had the same point of impact. But when I went to open the bolt, it would not lift. After hitting it quite hard with the heel of my hand several times it finally lifted and I was able to eject normally. Cartridge looked normal with no flat primer or anything different than the others. Brass was Lake City. Any idea why this one round stuck?