If the stock has a FACTORY finish, then it is probably polyurethane. That is as good as it gets, as regards waterproofing/ water resistance. However, the makers of mass production stocks (for mass produced rifles) often do NOT apply the finish well to the INSIDE surfaces of the stocks. THAT is the point of concern. I'd strongly advise, if you intend to take the rifle out in adverse weather, adding a couple of coats of finish on the INSIDE surfaces. No need to get fancy with this - just use spray polyurethane.
As for the oft misunderstood nature of unsealed wooden stocks and moisture... here is a bit of useful info. Yes, wood to be used for stocks is usually kiln dried down to roughly 15 - 20 % moisture content (depending on species - walnut is usually dried to around 17 %, for example), so to stabilize the dimensional characteristics of the wood. Wood - ANY species - WILL absorb moisture and swell, if left unsealed. The kiln drying process is NOT some permanent fix. If the moisture content of the wood is not maintained at approximately the same level as when the stock is made, then shrinking (if the wood dries) and swelling (if the wood absorbs moisture) CAN and WILL occur. The only way to prevent this is by SEALING the pores of the wood. Thus, the moisture content will be kept constant - and the dimensional characteristics of the wood will be kept constant, through a pretty wide range of temperatures.
The problems that occur with wood stocks (at least, properly made ones) "moving" and changing POI because of weather is ENTIRELY due to changing moisture content of the wood. Wood does NOT shrink and swell simply due to temperature changes, at least, not within the range you will ever encounter in nature. MOISTURE change is the culprit. SEAL the wood (ALL surfaces, inside and out) - and NO problem. Unfortunately, many (the factories included) tend to neglect the inside surfaces.
As for what I do with my stocks : I prefer an oil finish, on the OUTSIDE. But, I apply paste wax (often paste wax mixed with a little turpentine - several coats) on top of that. I have NEVER had a problem due to weather conditions. Do NOT depend on an oil finish, without some augmentation, such as paste wax. For the INSIDE surfaces, which won't be seen, I always use 2 or 3 coats of polyurethane. As I said, I've never had a problem, through rain, snow, what have you.
Last edited by wpsdlrg; April 10, 2013 at 05:30 PM.