I have not re-finished any high end walnut yet .Just acouple of Rem.788s and an old single shot .22 that my father -in law gave my son I just use regular paint stripper to get the poly coat off .( I am assuming that yours has that finish) repeat the process untill satisfied.Then I start the sanding.I tried to start wth the 120 grit.But you might as well save your time and start with the 50 grit.You will end up going back over it anyway .The 120 wont take out the deeper scratches.You can take a Dremel and clean up the barrel channel CAREFULLY.I usually finish up with 400 or 600 grit.How good and smooth the wood gets depends on how much you want to sand.

The Minwax Red Mahogany stain gives a nice color finish .