If the caps fire after you strike them more than once, they may not be seating right. I use #10 Remingtons on my Uberti "58 Remmie repro. They seat well but I have to pinch them a bit to keep them from falling off. I've read that CCI caps cause problems for some folks, but I've never used them myself. If you have never removed the nipples, you may need to spray them with a good penetrating oil and let them sit awhile. I've yet to find a nipple wrench I can't break, so you might want to have more than one on hand. I put a tiny bit of anti-seize compound on mine when I reassemble, be careful not to plug the holes with it. Good luck.