I would be careful with some of the suggestions posted here. The oil finish that you see drying out on your Berreta is nothing like the polimerized oil finishes suggested here. The thin oil used on these older guns absorbs into the wood and leaves very little surface finish, it would require very many coats to see any aprecciable surface buildup. I do not believe that Linseed was used in these guns and I would go for a thinner danish type oil that I suggest you rub in very well, do not leave a surface film but simply "wet" the stock. If you over do it then going whole hog with a built up finish will be your only salvation because the stock will start to show spotting from the oil filling up the pores, this is another can of worms altogether. So go thin, rub in and no surface built up, make shure you wipe off the surface oil.
IMO
bigbull