For old guns and military stocks it's boiled linseed oil. That's what was used, and has been used, for generations. To rejuvenate an old oil finish all you have to do is rub some in with fine steel wool and then with an old tee shirt. the old saw is still accurate: "Once an hour for a day, once a day for a week, once a week for a month, once a month for a year, once a year for life." That's how you apply linseed oil on bare wood. To rejuvenate an old finish steel wool on a coat, let it soak in, and rub in another. Wait a week and see what it looks like, if it looks dry add more oil. if it doesn't check in a month. Just pick up the routine when it begins to look dry.
For a new stock I'd use tung oil.
Wayne the Shrink
