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Drying oils such as Pure Tung Oil (as distinguished from so-called tung oil finishes) and Boiled Linseed Oil are crummy finishes. They are aesthetically pleasing, cheap and relatively easy to apply, but offer only minimal protection for wood. The only thing worse is wax. Beeswax/BLO blands like Culver's Magic Paste are NOT suitable as a primary wood finish though they may have some utility as a top polish over a drying oil finish such as PTO or BLO.
So called Tung Oil Finishes may or may not have ANY Tung Oil in them. Formby's Tung Oil Finish, for instance is mostly solvent and varnish resins. There may be some oil in it, but if so, it is mostly for scent. Nevertheless, these finishes are generally a vast improvement over BLO and PTO in terms of protective value and moisture exclusion.
Polyurethane, urethane, and varnishes all work in about the same way. Urethanes and Polyurethanes are synthetic varnishes derived from Ureic resins. Spar varnishes often are blended with tung oil to yield better performance in outdoor environments where urethanes can break down under intense UV light. Varnishes are probably the most effective and practical finishes for hard use or competition grade stocks.
Glossy finishes can be toned down with the judicious application of #0000 steel wool, but don't cut through the finish to bare wood.
As far as applying pure tung oil is concerned, give yourself plenty of curing time between coats, a minimum of 24 hours under warm dry conditions and as much as 3 or even 4 days under cooler and or more humid conditions. BLO cures a touch faster thanks to the addition of chemical driers, but BLO is a marginally less effective finish. You can speed the cure time of PTO by adding a small amount of Japan Driers (available from art supply and paint stores), but you may have to increase the number of coats.
DO NOT attempt to build PTO or BLO on the surface of the wood. This is a recipe for disaster. Neither of these oils cures well enough for surface building and will feel sticky and soft pretty much forever if you do make this error. If you accidentally build oil on the surface, rub it down to the wood with steel wool or 400 grit sandpaper. Buff sanding between coats will limit building the oil into a film, it is also a pretty good indicator of how well your finish has cured. Fully cured oil will sand off as a white powdery substance while poorly cured oil will tack up and clog the paper or sand off in tacky strings and balls. The same is true of polyurethane and varnish BTW.
Polymerized oils like Tru Oil, Linspeed and the Tried and True brands of polymerized oils are linseed or tung oils that are either chemically or thermally modified to improve their characteristics. They tend to cure faster, harder and more resistant to chemicals and moisture. They can be quite glossy or fairly satin depending upon the formulation. Tru Oil tends to be quite glossy. Tried and True offers a variety of products ranging from a Danish Oil type finish to a full on Varnish grade finish.
For a hard use rifle stock I would recommend finishing with outdoor formula polyurethane for maximum practical protection.