I had this same problem with a brand new OA. Out of the box, it would only fire caps about 50% of the time. It only got worse and after about 3 or 4 cylinders it would only fire about 25% of the time. Ruger sent me some new nipples that did not help. Not wanting to have my gun tied up at Ruger for who knows how long to MAYBE get it fixed, I sent it to Dave Clements (Clements Custom Guns). I thought my mainspring seemed week, but according to him it was fine. He did, however, find that my hammer was too thick and left no clearance for dirt or debris. He relieved it 6 thousandths, to allow it to work with a little dirt, and relieved it to strike closer to the nipples. The latter, I believe was due to the fact that the cylinder was setting a hair futher forward than normal. The reason I think this is because I also sent a friend's cylider with my gun to have the chambers deepened. He tried both cylinders in my gun and his set back further than mine. Go figger. Anyway, he tested it with a couple dozen caps and it should be good to go. I'm hoping to get it back this week so that I can work up some conical loads for deer season.