I have had similar problems with my Xtrema 2. My 2 3/4inch 7/8oz reloads were not firing every 3rd or so round. The fiocchi 209 primers had light strikes on them. I had never had a mis-fire before with any brand of ammo, i have even shot a case of Kent through it no probs.
I thought i had fixed the problem by disassembling the bolt and cleaning it completely. Even on the inside of the pin hole (thinking that dirt was keeping the shoulder of the pin back). unfortunatly it was still light striking.
I have since replaced the main hammer spring as i always left the gun cocked (not loaded) in the gun safe and i suspect the 1st owner of it did the same. I think the original spring was compressed and weakened by this. I have fired 25 reload rounds with no problem since then