there are Oak stocks, the Germans used a lot in WW11. the point is, there is a lot of better wood available . why bother with oak ,even if the wood is free.
The stocks you are talking about, were Elm, not Oak. Other nations used Elm as well.
As far as Oak for a stock goes, it will work fine, as long as it has been dried evenly and sealed properly. The same goes for any wood.
I had a Lyman 50 cal Plains Rifle stocked in Oak. Yes, the thing was very heavy. It was stable though. It also made for a very steady hold on targets at the Rendezvous. Especially with the off hand targets. There is a lot to be said for a heavy rifle at certain times. I never did hunt with that rifle. I wonder where it is now. When I decided to get into Hunter Bench Rest, I sold it to help fund my first rifle.
Another wood that is frowned upon for a rifle stock is Cedar. Well, I can tell you from personal experience, it makes for a very light and tough, stable stock. Just depends on how you finish it. Back in the early sixties, I was given a half dozen 22 Cooeys. Every one of them, especially the Rangers had broken stocks.
In those days, one of the local sawmills used to allow anyone that wanted to take the time and go through the effort to root through their discard piles. The rough cut boards were OK for firewood and many people heated their homes and cooked their food with it. The planed and dry kilned wood burned well but didn't throw any heat. Most of the liquids had been evaporated out of it, which also created the wood gas that created most of the heat when burned.
There was some very nice pieces of wood in those piles. They cut a lot of Birch and even some Willow and huge Cottonwood on special order. There was a lot of it in the country in those days. The Willow and Cottonwood went to a special Linear Planer in Kelowna. Everything was planed on the quarter grain so that the grain would stand out for paneling and furniture. They only wanted certain sections of the trees for those purposes and about 70% of the log was scrap.
Cedar, was mostly considered to be junk wood and only the dark heart wood was considered valuable. Most of it was for export.
Some of the second growth Cedar had lovely light and dark lines through it that were naturally occurring. All beautifully straight grained and above all else, easy to carve with the limited tools available to the hands of a teen.
The first 22s I carved new stocks for were of kiln dried Cedar. The rifles they went on were a dream to carry but damaged easily. A neighbor, asked me why I didn't apply clear coats of fiberglass resin to the wood. I had never used the stuff on anything and honestly, didn't know where to start, let alone know how to apply it or where to get it.
Being the good fellow he was, he took me under his wing and when he was putting a coat of resin on one of the gorgeous Cedar row boats he made as a hobby, he called me over to apply the first coat on the stock I was just finishing. That stock was bone dry. It soaked up the resin like a sponge. Even though the stock had been sanded smooth, as the resin cured, the wood feathered. A quick sanding fixed that but of course, the finish was ruined. This meant another coat of resin. I have no idea where that resin went, but it didn't even look like it had been applied. Two coats and sandings later and it started to look pretty good. The fifth coat was extremely thin. When it dried, it was almost but not quite shiny. Perfect.
It was also tough. The finish on those stocks would take a lot of abuse and wouldn't dent. They scratched of course but that was easily fixed. The stocks were almost as good as the later fiberglass shell models that were either filled with foam or left hollow.
I still see a few of those stocks around. My stepson whom I gave one of the rifles to at 10, still has his today and he is now 45. The stock is scratched and battered but still tough and perfectly usable.
Oak leaves a lot to be desired as a stock wood, but if you take care to finish it properly, it will do a yeoman's job.
As far as rot goes, I have a White Oak table, made out of old 3inX8in boards from scrap machinery pallets. It is untreated and out in the weather. It has been there for close to 40 years. It is gray, covered in saw cuts and hard as a piece of steel. Not a sign of rot. It is on a concrete slab though and I do believe if it were on the ground, it would likely be rotted away a long time ago.
Willow and Cottonwood can also be very good, as long as the grain is straight. They both have some incredibly lovely grain and they have to be very carefully cured before using. If you think that Cedar soaked up resin, the Willow and Cottonwood take up twice as much.