Here is my method for a completely waterproof finish, now this is NOT wear proof, no wood finish is wear proof. It is also NOT PC so if you're a purist stop reading now.
1) Coat the stock thoroughly with Thompsons Waterseal, in lock mortices, barrel channel, pour some down the rr hole, saturate it completely, let is soak a while and keep applying to areas that soak it up. Let it dry over night.
2) Do #1 again, let it dry over night.
3) Mix TWS 50/50 with Formbys low gloss Tung Oil, apply to all areas, lock mortice, barrel channel etc.....wipe it off and let ot dry over night.
4) Do #3 again, let it dry over night.
5) Use pure Formbys and paint it on, inside lock mortice, barrel channel and hand rub it into exposed areas. Let dry over night.
6) Hand rub your next coat(s) of pure FBYs'on extieror of stock surfaces only. Let it dry over night.
#7 Repeat #6 as many times as necessary to give the finish you desire.