500Nitro,
Thanks for the good advice. I guess I didn't state my idea properly, what I intended to say was that we wanted to chamber the gun with the three inch reamer, and use the tree inch shells as is, but load them up using some filler to about the same loading as the 2 3/4 inch loading. I went back and changed the wording. I do know what you are talking about with the chamber being eroded.
Do you see any problems with this method? I would still mark it and proof it for the 2 3/4 inch loading. If I load the 650 grain bullets in the service loads, but use some 750 grain bullets over the standard powder charge to proof it, that will give me about 115% of the the service load for pressure, or 15% over the service load. Two of those fired down each barrel should be sufficient to proof it. Do you agree with that method? Bob