This past weekend I took my late father in law's Savage 99 out and sighted in the iron sights. Started with some Winchester Supreme 168 gr in 308. No problems. Loaded 5 rounds of some older ammo of his .First two rounds no problem.Third round huge boom and recoil I am still feeling. Last two rounds sounded louder but no increase recoil. I realize I shouldn't have shot the last two rounds. Upon looking at the third case I saw a rupture near the base of the cartridge. I looked over the rifle saw no cracks or bulging.Should I stop using the rifle ?Just stick to newer ammo?