The WW-2 cutoff for considering a gun for steel shot has sort of been my measure too. However, you also consider the barrels you actually intend to use; the Stevens 311's all seem to have been built with extra heavy barrels (or 'Hell For Stout' as Jack O'Connor put it) while other makes used more 'refined' barrels.

Short answer: by the end of the 1940's the steel was about as good as it is now, but if the barrels are thin walled and the choke tight, don't do it...Geo