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  That's a great idea for locating the pin Richard, hopefully all the pins are placed the same. Goon's got a good point about welding. My beater pistol is a beater because, among other insane experiments, I decided to try welding out the Pieta markings on the barrel with a mig welder and flux core wire, made a real mess.

  If the solder proves too soft on its own, you could try using it to sweat in a piece of steel,  duck soup since the slot's already tinned.

I had it happen once, when I thought it would be a good idea to press some "bullets" out of powder and load them into a navy Colt to shoot off for the 4th of July,  not one of my better ideas!

  No issues with stock Pieta nipples. I savagely abused a set firing corrosive caps, and though they still worked fine (but looked ugly),  I replaced them with more Pieta nipples, no problem.

  Whip,  you could put some screws into a small kitchen sieve and try that first, though it takes larger parts to really get a sense of what the colors are like. It requires quite a bit of nitrate, since melting the stuff is rather like melting snow down into water, there are probably cheaper sources of KNO3 online, I just go to Lowes for mine. The only durability problem so far for me has been with the grip frame of a Pieta '61 Colt on which the nitre bluing wasn't as durable as the factory bluing, I'm going to try brass plating on it using the method Richard suggests. My guess is that it will take a while to get enough nitrate melted to blue large parts on a grill burner, and that heat rising around the vessel which contains the molten nitrate will make lowering and raising parts into the bluing bath a bit tricky. I made my melting vessel with a rim which sits on some insulating fire bricks;  makes it safer to work above, and heats more quickly. Being the impatient sort, I help my burner accomplish the initial melt using a propane torch. Once you get the nitrate melted the grill burner would probably do a fine job of keeping the salt melted and at the right temperature. You'll need some sort of frame above your melting tank so that you can suspend the parts in the solution, you don't want them touching each other or the bottom or sides of the melting vessel, I use a steel rod above the tank as a frame, and hang the parts from it with black iron tie wire.
 

  Whip,  I've got both the Pieta and Uberti 1861's, the Pieta is a joy to shoot, haven't fired the Uberti yet. I prefer the lines of the '51 navy though, so that's what I'd buy if  could only own one percussion revolver.

How bout this Richard:

chamber 1. hot cap, Black MZ, ball.
chamber 2. hot cap, Olde Eynsford, ball.
chamber 3. hot cap, Olde Eynsford, over powder wad, ball.

Chamber 1. tells you whether or not it's the Black MZ alone. Chamber 2. tells you whether it's "any" powder. If 1, 2, and 3 all fire, it's Black MZ and the wad working together. I don't see how Black MZ can dribble down each nipple, penetrate the sealant over the priming powder, and kill the cap every time. A vapor though, sealed tightly in a chamber with wads and a lead ball would take the path of least resistance and go right to the cap. A liquid would do the same, but would have to saturate the powder before arriving at the primer, and then penetrate the primer, I'd expect that to kill the whole charge, which didn't happen. Final possibility is that the hot caps have a very limited shelf life, and you're the first to notice it and post about it. It could also be the number of cats, don't know how i missed that possibility.  ???

  You might want to treat the wads as a variable too Richard, something could be out-gassing from the wad lubricant and reacting with the caps, or reacting with something in the Black MZ which in turn is reacting with the priming compound in the caps. I think your suspicion regarding the corrosive nature of Black MZ in contact with brass has merit, but you really can't safely rule out anything just yet, with the exception of the bullets. Something I automatically do with the home-brewed components I sometimes employ is to store them (powder excepted) under refrigeration at around 35 degrees fahrenheit. You might try keeping one loaded cylinder inside a baggie in the refrigerator to determine whether the suspected chemical reaction that's potentially killing your primers is affected by temperature.