Well it seems we now have this clunky block hanging on the end of our stock. We need to make it smooth and sleek. First. Protect the stock. Wrap multiple turns of protective tape around the stock. Four layers at least. In these next steps, if you start to tear up the tape (you will!) stop and re-wrap. If you’re going to blend the extension into and try to match the stock, then you’ll be refinishing the whole thing, but you still want to avoid large gouges and scratches.