If the hard to fit caps give 100% ignition then how can the hammer be at fault? A stronger main spring may push down a poorly fittting cap and still have enough force to explode it but it sure seems to me your problem is a poor cap to nipple fit.
Someone once told me the hammer on a colt was supposed to stop just a hair short of the nipple, to prevent the nipple from getting beat up if the hammer fell on an uncapped nipple.
I had an old gun where the nipples were sort of tapered and you had to pinch on the caps. That's ok at a range, I guess, although a chain fire might occur, however loose fitting caps are a no no if you want to pack the gun in a holster. I got some after market nipples- Uncle Mikes I think, and never a problem after that.