[Unclenick]

Have to throw the opposite opinion in. Linseed oil takes a water mark really easily which means the moisture permeates it. I was surprised to learn this, as it has been used on guns for so long, but I got it from a book called Understanding Wood Finishing by Bob Flexnor, sold by Woodcraft. He shows a picture of the watermark effect, so I tried it on a scrap and got the same thing. I have vague memories of a .22 I used as a kid that had a BLO finish and that got streak marks in rain and need more BLO rubbed in.

Flexnor rates the water and water vapor protection as follows:

Linseed Oil - Poor
Boiled Linseed Oil - Poor
Pure Tung Oil - Poor until 5 or more coats are applied (over a month's work)
Polymerized Oil - Potentially excellent if built up
Oil/Varnish Blend - Medium
Wiping Varnish - Potentially excellent if built up

His examples of polymerized oils include Birchwood Casey Tru-Oil and Polymerized Tung Oil of any brand.

His examples of wiping varnishes include Watco Wipe-On Poly, Formby's Tung Oil Finish (note that this does not contain tung oil, but is so-named for its resemblance to a tung oil finish when dry) and General Finishing's Seal-A-Cell.


Since Birchwood Casey Tru-Oil is made for the gun finishing market, I expect you will be more satisfied with its appearance than the others that can be built up for water resistance.

As to the best method, back when the M14 was still the king of the service rifle match hill, the AMU used to finish wood stocks by putting them in a container filled with a single-component clear epoxy finish, and pressurize it at something like 100 psi (air compressor). After several hours (maybe a day - I've forgotten), they were removed and wiped off, then baked for a long time in a low oven. Seems to me that might have been for two or three days to harden the epoxy. The single component epoxies are slow to dry.

For most people the cost and equipment requirements make that approach a non-starter. Just thought you'd want to know what was done for practically zero humidity creep. I don't think I'd do it to a sporting rifle, anyway, because it will add noticeable weight. That's good for a target rifle, but not so good for something carried in the field.