[Dan]

I am also new to the world of Parker's so what I have to say should be taken lightly. Assuming this is a single selective trigger it is possible that during recoil from the first shot the selector is moving enough to switch barrels which in essence means your trying to fire the same barrel twice, that may be why the snap caps work, no recoil involved. I believe the selector can be tightened enough to prevent it from moving during recoil. Hope that is your problem and nothing tougher....