I have done literally hundreds of pewter tips on a reproduction brass suppository guns sometimes 10-12 at a time. And some on 1/2 stock MLs. Never had problems with discoloring the wood. Though most were walnut. I also stopped using any lead bearing material, did not want the bring the dust home to the kids. Real pewter, the food grade stuff, does not “gray” the wood like lead bearing solder. I used a LOT of Silva-Brite 100 lead free solder which is actually identical or very close to one of the old real pewter recipes and never darkens as lead bearing solder will do. But usually the gray can be removed with something like steel wool, or I assume scotch brite.
I would file to shape, fill any holes/pits with a hot piece of brass rod (unless really bad then melt off with a heated brass rod/soldering iron and recast), file again, sand to 220-320 then burnish. This will show any near the surface voids and erase a lot of scratches, then go on to finer grits and then 0000 steel wool. And since the wood has been heated and moisture driven out the the area adjacent to the cast the second pour is usually pretty trouble free. If the cast comes in contact with the barrel then the barrel has to be heated well at the area around the pour as it is a massive heat sink.
The lead free solder is higher melt temp than lead/tin. I would heat in a stainless steel grocery store ladle, bend the handle as needed, then stir with a piece or pine (slivers of pine were used as part of the dam along the side flat) when it scortches in a few seconds its hot enough. This also moves any dross from the pour side of the ladle. But remember the barrel was a heat sink and the way I poured these to prevent them “moving” under recoil there was a lot of barrel contact. On a ML half stock with a lot of barrel contact the metal will also cool a lot faster. I suspect that the complex SMR type shown here will need the metal well heated as well.
