What are you lubing you cases with? Being that this was the only misfire and that your primer didn't go off (assuming there was sufficient impact from the firing pin) and your powder was caked you definately got some contamination. I would suspect either case lube or oil got into the case somehow and contaminated both powder and primer. You're fortunate in the fact that everything got contaminated and not just the powder. A primer will generate enoughenergy to lodge the bullet in the barrel. That happened to me with some contaminated RL-7 powder which I got new from a local gun shop.