Oak is very heavy and an oak board will almost literally walk across the floor. Oak is pretty unstable.
Hickory has been used on RARE occasions as a gunstock...by those foolhardy enough to attempt to use it! Hickory is incredibly hard, and therefore, harder to work than some of us mere mortals care to try. Rich Pierce notwithstanding...I think he's trying to reproduce the hickory stocked Bucks gun... :wink:
Beech is OK for stocks (and was used for military stocks, and is still used on European rifles for lower grade guns). Super hard, but brash and unpleasant to work. It's also got lots of flecks and rays that can be quite gaudy.
Birch makes an OK stock, but unless it is curly, it is horribly, horribly plain and unattractive. Often used in Scandinavia, but apparently they have a somewhat higher incidence of curly birch than we have here. Most cheaper grades of American guns have had birch stocks for decades.
Ash makes a fine stock. Hard, not quite as heavy as oak, and seems to be relatively stable. The porous rings do visually interrupt carving, but it can be done. Ash was used on German rifles on RARE occasion, and perhaps on a PA rifle here and there, but there seem to be several old Tennessee/Southern Mountain rifles stocked in ash. The English used ash in the 17th century a good bit to stock guns with.
I have a curly ash stock blank here that I have not yet done anything with. I have a straight-rifled barrel ordered that I think I'm going to put in it...