1851 uberti navy misfiring

[hawkeye2]

1075 caps are RWS and available here in the US.

 

[M. De Land]

The hammer is making contact with the cap. Seems the impact is at the top of the cap.

Repeated impact causes the cap to have a bit of a mushroom only at the top.

You might want to try removing the nipples and putting each one into a hand drill motor, spin and clean up the top, out side edge of each, against a stone. Turn a bit then test cap fit with each. I think the bit of angular strike from your hammer face has raised a flat on the nipple edge that is keeping your caps from seating all the way down. It isn't going to hurt your used nipples any to try this. A little goes a long way here so test cap fit often.