Although technically not BPCR, it is the same part on 1859/63 and 1874, so I thought this might be the best place to ask. I picked up an original 1859 Sharps that is still percussion and noticed it would not hold full cock. I took it completely down, and found the tumbler has a broken full cock notch. The half cock notch and sear are in good shape. The main spring has one of the ears broken off, so I am guessing it was dropped on the hammer while cocked some time in the guns 150+ year old history. Right now, S&S, Lodgewood, and Dixie don't show stock of an original tumber. I can either get a repro and fit it (not a bad idea, it just isn't an original part) or file the notch deeper in the tumbler. It will be shot a little but not much. It is a rare Union Navy carbine, and I do plan on getting an original 1859/63/74 tumbler when one does show up.