Ted, not one hundred percent sure but I think You can only request black powder proof if the gun had only ever been proofed for black; once submitted for nitro at some time in its history then it has to pass a nitro reproof.
I think Toby is taking the sensible option. His reputation would have taken a knock if he had sold the gun and it had failed after a few rounds with its new owner. Better to fail in a controlled environment.
I sold a good strong steel barrel hammer gun a few years back. It was 1 thou. out in one barrel so off to the Proof House it went having the chambers lengthened from 2 1/2" to 2 3/4". It passed no problem as I was sure it would. I sold it on and the barrel bulged and split just forward of the forend during use. The gun was returned to the Proof House for inspection and they concluded it was due to a barrel obstruction. Having it re-proofed prior to sale indicated that I had at least not sold a gun in a dangerous condition.
I have only ever had one gun fail and that was a 20 bore that cracked at the action at the angle between the standing breech and the flats. It was repaired by stainless steel welding in the gun trade and re-submitted and this time passed. It is almost impossible to see the repair other than with a magnifying glass. I have sold it and given the buyer all the details but having passed re-proof both he and I are confident that it is good for use. Lagopus.....
