I've had the sad experience of seeing a couple of rifles and even an M2 blow up over headspace/pressure issues.Heed WildRose's advice. Pressure is a bad ju-ju and a sticky bolt is usually a good sign it's getting up there. I would run it into my local gunsmith explain what's happening and have him evaluate the rifle. If it's something simple have him repair it. Anything beyond that send the rifle back to Rem.
Extremely doubtful. You would in all likelihood easily observe (before loading them) damage to the base or rim if it where there or if some of them are markedly thicker based.also this just came to mind do you think maybe its the ammo cause i do recall it would operate on some shells.