They will work. I've loaded .308 diameter bullets to use in an SKS on and off for several years, 110 grains to 150. Accuracy seemed to be the same as with .311's, but with iron sights, aging eyes and the SKS it may (or may not) have made a difference.

Slightly undersized jacketed bullets can usually be worked with; undersized cast bullets are a different, and ornery, breed of cat.