It does increase the pressure on the nipple to put some powder in the drum. I have filled the drum up with powder, and had the hammer blown back to recock position!
So after that I just put a llittle powder in there. In my initial post I was going to say I put 5 or 6 grains of powder there but I did not want to cause confusion. I don't mean 6 measured grains!
I mean, I put 5 or 6 little, individual specks of black powder in there. Doing that, I got 100 per cent ignition, but it didn't blow the hammer back to recock. I could tell of very little, if any, extra blowback from the nipple.
Now I would only fire the rifle loaded in this fashion maybe ten times a year, and I did that for maybe ten years.
I never blew out the nipple, that would have put the fear of God into me for sure.
I was shooting a TC Hawken, possibly it is stronger than the Spanish made CVA, I don't know.
Come to think of it the cap and ball revolver is loaded this way any time you shoot it. You have 30 grains of fffg sitting right inline with the nipple, and those nipples don't blow out.