I was zeroing a .223 stevens this evening, Ultramaz remanufactured ammo, 55HP, and a case blew! No harm to me or the gun, but left the case neck in the chamber. I have used oversized brushes, poured a chamber cast, even used a .22 lead slug backwards from the muzzle, no luck. I have used these techniques a dozen times when a full time gunsmith, never failed. I guess I may pour another chamber cast with a brush, and then freeze the barrel overnight. All feedback welcome.