A few years back we bought a really nice Pape 16 bore thumb lever hammer gun . 30% original case colour,original brown on the barrel the stock had very fine ornate checkering that although slightly worn was all there . It was of course black powder proof. We sold it to a collector on the condition it passed nitro proof as the only fault was that the barrels were pitted. After boring they were almost perfect,it was decided that as the current proof pressure is the same for both 2&1/2 & 2&3/4 chambers to chamber the gun to 2&3/4. it was submitted to proof . On return the barrels were still perfect ,the action came back in several pieces in a plastic bag.
I realise you do not have to reproof a gun in the States if you do lengthen the chamber ,but there is sometime more to consider than the barrels.
