I don't think any Oil finish is water PROOF, including Linspeed. I stopped using that finish in favor of Birchwood/Casey Gunstock oil finish. Its thinner, rubs into the wood pores easier, and has a longer working time, IMHO.
If you want any stock to be somewhat water proof, put finish on ALL end grain, and in all mortises you cut for ANYTHING.[Buttplate, capbox, tang, barrel, muzzle cap, hangers, thimbles, entry pipe, trigger guard and lock. ] Then give the finished stock a few coats of a good furniture or "antique" wax, before going out in the " Wet". The same wax on the metal parts will help stop rust from occurring in the field. :thumbsup: