I have a '51 Navy in .44 that I bought used. It has never quite worked right. It was alleged to have an "action job", and it does have a cap stop installed. Discharge has always been intermittent. First, the hammer would not go all the way forward and jammed up the rotation of the cylinder. I adjusted the nipples that were on it to fit the caps perfectly and that problem went away, but the failure to fire ratio still happened. I changed to different nipples from TOTW. Reduced the incidences even further but still not 100%. Emailed Pietta and got a lot of questions and info. After answering everything and following the suggestions I got new factory nipples for $16.00. The FTF was now about 1:40. I was wasting a lot of caps but at least I have thousands and it was worth it to me to get this running right. Told Pietta what was happening and they asked me to look at the mainspring or I think they called it backspring in the emails. Mine was a split spring. In other words, it had a cut-out along the middle length of it. Whomever emailed said he/she was not familiar with them ever using a split spring for the "backspring". They offered a new one for $16.00. They also had me look at other parts and report any differences to the diagram they sent. Every else looked good and the timing was tuned right. The backspring arrived and installed easily. The revolver ran perfectly all day today. I fired far more rounds in succession without a hiccup than ever before with this revolver. I guess reverting to factory specs was the right remedy in this case. BTW the cap-guard works well, I had not problems with a jam.