JS47 wrote on Aug 28
th, 2018 at 10:58pm:
The vacuum removes the air which lets the resin or finish flow into the wood when the vacuum is let off and the pressure is applied. A common "Food Saver" won't do it. It doesn't pull enough vacuum. I gave a description of the method we used with a tank made of 6" plastic city water line and a vacuum/ pressure setup some time back on the forum. It worked great for stabilizing wood during drastic changes in weather but was pretty expensive so we quit doing it. My rifle has been living in 50-80% humidity all it's life. I'm a little nervous about what will happen to it over a winter in southern AZ. I'm afraid it will shrink up like my 95 year old mother.
JS
Agree that IF one wants to use vacuum removal, one needs really effective equipment. Perhaps best followed by pressure injection of sealant.
As regarding moving guns from high to low or low to high humidity, those are just the kinds of changes in ambient conditions that lead well known riflemen, such as Jack O'Conner , to sealing the interior wood surfaces on their rifles. Basically this means ALL the interior surfaces, which on every new rifle I ever bought in USA were totally bare wood and highly sensitive to changes in humidity. These bare surfaces also soak up sealent fluids, such as stock finishers, really well. Even more likely to result in stock warpage is stocks made from fancy wood with grain patterns far from purely straight grained. Also, remember that during O'Conner's time as gun writer, it was common to use "shims" in barrel channels to control vibration patterns, perhaps leading to increased chance that shrinkage/swelling of bare wood would result in unwanted changes of POI in precision hunting rifles. As I recall, free-floating rifle barrels was to be the ultimate solution to such problems.
If one believes the rationals given for laminated stocks, and they do sound quite correct IF done properly, then that is one more way to get really stable stocks. Perhaps the logical extreme for wood stocks.
If, one is simply trying to prevent shrinkage of stocks in purely collector guns, then the techniques and practices of major museums are highly recommended. I would presume that NRA HQ collection uses such practices.