Malmute has ID'd the cause
I'm a little bit surprised that Grayrock didn't have success with both guns, but that's no dig at him at all
The BM pins are just plain better made to tighter tolerances, including the slot for the latch.
I would recommend getting the standard, non-locking pin that Grayrock mentions and ordering a pack of three extra-strength springs from Wolff or one of the usual suspects. This will solve your problem almost certainly (but see note below). I would not recommend the locking version unless you are prepared to mill a hole in the underside of the barrel. If you don't, you'll be flexing the pin and barrel slightly when you crank down on the screw to lock the pin. The gun just wasn't designed to work that way. Take a look at a Freedom Arms if you want to see how that system should work when fully executed.
My note: I've installed several non-locking BM pins and had great luck, but the most recent triggered an issue with a Vaquero...turns out Ruger drilled the front and rear holes in the cylinder frame slightly out of alignment. This was not a problem with the significantly undersized Ruger pin, but makes the BM pin, which is to the max spec, very tight. So, a caution: tightening up the pin spec may have some unintended consequences that you didn't see with all-factory parts where looser tolerances offset each other. The real implication of that is that if you want a SA revolver that's built to really tight tolerances, buy an FA, not a Ruger -- but that wasn't your question. Try Malmute's suggestion first, then Grayrock's if that doesn't solve your problem...these gentlemen have given you good advice.
