You might try backing the nipples out a turn or so to decrease the distance to the hammer and see if that ignites the caps better.Thats only for diagnostic purposes with empty chambers. I suppose you could shim them out a little if it shoots better like that. You might also try some different brands of caps. I had a pistol which the hammer rubbed on the left side of the hammer cut. I sent that one back for that and a multitude of other reasons, but something like that can decrease the hammer strike enough to cause problems.