@Prairie Dawg, SASS #50329 thanks for that link it's very interesting. My biggest take away was (my question to follow)
I measured the Uberti and Pietta nipples and compared them to stock. The Uberti SlixShot measured about .032 longer than the stock Ubertis. The Pietta SlixShot only measured about .006 longer.
I haven't tried the Uberti with the SlixShot nipples yet - ran out of time at the range. I did run about 72 rounds through a Pietta 1860 Army. I fired three cylinders full with Remington #10, Remington #11, CCI #11, and RWS 1075 caps. One cylinder with each size cap was capped with a TDC revolver capper, one with a TDC dual spring straight line capper, and one capped by hand. I did not use a "seating stick" or anything other than the capper or my thumb to seat the caps. All of the caps went on without any trouble and felt like they were a snug fit. I slow fired the first cylinder full with each size cap and didn't see any evidence of unfired caps backing off the nipple.
The load I used was 30 gr. fffg Goex thrown from a flask with a 30 gr. spout (which weighs out to 30.3 gr.); Ox Yoke Wonder Wad, and a .454 round ball cast by BPstuff llc. Every chamber fired first time. All of the Remington and RWS fired caps looked like a plus sign. Four evenly sized wings coming off the center. Most of the CCIs did the same; but some of them disintegrated or didn't split up completely. The only two instances of a cap falling into the frame/action, was with the CCIs that didn't split up completely on firing; but, they didn't jam up the gun. The hammer just flattened them to the frame. In every instance, the only cap still left on a nipple was the one under the hammer from the last shot. All of caps fell off, and none got between my hand and the grip.
The 1860 I used was 1994 vintage that has been worked over some using Pettifoggers procedures. It has coil spring & plunger hand spring and the hammer notch is filled with JB Weld.
I'm going to try to get back out to the range later this week & run the same process on my Uberti 1861 Navy. Hopefully the extra length won't be a problem. My 1861's have been worked over like the 1860s, so I'm going to take one of my .36 cal Piettas that is still bone stock unmodified & see how the nipples work on it. I'm also going to try a couple Wolf reduced power hammer springs & see how they act. This time I'll take my camera too.
So far, I'm really liking these nipples.
So am I reading this correctly that on the SlixShot nipples both Remington #10 and #11 and CCI #11 should work well? Also I'm using on .44 Pietta Remington NMA.