Raul said:
The nipples are Treso. They work with rem 11. Ran out, so order RWS 1075. I didn't file down the top, only the "side". It is an Uberti navy london. The tear was not around the edges, it was in the middle of the top of the cap. The tear was triangle shaped, sort of. Location was were the hammer slot would "hit".
I'm presuming this london navy is a .36 cal and normally has #10 nipples from factory.
You converted to #11 (based on treso).
How long you been using the treso's and any other noted issues before the filing?
The safety notch in tip of hammer face, should not strike the nipple at all, except maybe on the very upper edge of the nipple,because you went to #11's which could be a tad taller nipple ans is arguably a shade larger in diameter. But I doubt that, let alone in the center of top of the cap. But without seeing the revolver, it's just a guess.
..
The top of the nipple is not exactly flat.
It is slighty contoured and the edges are rounded.
By filing the sides you changed the configuration.
The edges are now more sharp. the hammer impact is going to cause the tearing.
But you didn't mention why they did not fit.
Were they too tall and would not fit down, or what.