I put new stainless nipples on my 1858 Remington Navy Arms repro, about 15 years ago. The originals were soft and mushroomed, and the caps wouldn't go on anymore. Since then I've had zero problems with caps/nipples- also the caps stay on the nipples better, they are slightly larger in size.
Other than being soft/mushrooming out, the other reason to change nipples is a more correct size, so they hold the cap without falling off- and also for a smaller charge hole inside, so the blast of firing the gun, doesn't blow the hammer back. Last time I shot my Colt 1851, it was blowing the hammer back to badly, it cycled the cylinder to the next chamber, and the hammer was resting half way on the next chamber's cap.
Years ago, while shooting a short-barrel 1851 Navy "Sheriffs" model, I experienced hammer blowback so severe, it cycled the gun to next chamber and fired it again automatically, like a semi-automatic.
I pulled the trigger once, it went "boom-boom" and 2 shots were fired.
This is a perfect example of improper half-aszed engineering, or lack of engineering, by the foreign mfrs. The guns should have stainless nipples from the factory, with the proper charge hole size to prevent blowback, and there should be no cap jams- not in guns costing $300-$400.
the American shooter/consumer has let these overseas mfrs. get away with murder, and when word finally gets around just how bad the quality of these guns is, their sales are going to suffer. They need to wise up, and fix some things. They've been shipping a lot of junk guns, for a long time.
BTW the stainless nipples I put on the 1858, were sold by a company called "Uncle Mikes"- but I don't know if they still carry them- they were a SUPERIOR product, way better than the Italian installed nipples
http://www.gunaccessories.com/UncleMikes/holsters.asp