BBls can be lengthened by turning & reaming opposite portions of the original & extension to about half the wall thickness & approx ½" long, then silversoldering together. This is of course much easier to do a single bbl than a double. For the double would likely need to make up a piloted reamer of correct dia to ream the ends of bbls & turn the "Tongue" on the extension. For a single bbl I normally do it the other way. Would want to make absolutely certain you left no Forward Facing step for wads to hang on. There would then of course be the problem of the rib. To put this much effort in an H grade would have to acquire it much "Cheaper".
