Folks, I'm not going to tell you I've actually done what I'm proposing here, so this is more in the line of an experiment -- Which I have done successfully on old furniture -- but NOT on a gun stock (only because I've never had the problem). What I am writing below is based on educated assumptions, not as an expert, but having some experience with this problem. Please correct me if I'm off base!
1. Kiln Drying: As far as I'd assume, military stocks are made of Kiln Dried wood (which was stacked and dehumidified), so that it is straight when taken out of the kiln and brought to the stock maker.
2. Linseed Oil: The reason stocks were hot-dipped for 24 hours in linseed oil was to fill the wood pores with oil, which limited their ability to dry out and possibly warp.
3. Why does wood warp? Unless it was put into a contorted position by force, wood warps because one side dries out (the wood cells contract) while the other side stays stable (filled with oil or humidity), thus twisting the wood.
4. What Steaming Does: Steaming puts moisture back into the wood, and hot steam makes the wood pliable. When taking out of the steaming vehicle, one twists the wood to the form one wants, lets it dry, and it should hold this position for years. (this is how a hooped back Windsor chair is made.)
5. What to do after Steaming: After steaming, twist the wood back to the desired position (perhaps a tad accentuated because it may have a tendency to snap back just a bit), and let it dry for 2-3 weeks held into this position to let the humidity stabilize. Once dry, dunk in 120-130 (F) [50 C]
BLO for at least 24 hours to fill the wood pores with oil.
This process should keep the wood stable for years to come.