The primary difference is the pistol vs. rifle cartridge chamberings, although the 336 was chambered in .44 mag briefly in the 1960's as the 336 Magnum Carbine and the 336T (not to be confused with the .30-30 336T Texan Carbine) before Marlin brought out the 1894 line in the late 1960's. The 1894 retains the square bolt and open-sided receiver of the 336's predecessors that date back to the model 1893, while the 336 has had the round bolt entirely enclosed within the receiver since the last significant model change in 1948/9 or thereabouts. Both have been produced in straight stock and pistol grip configurations at various times, and I have examples of both. The 336 is also the parent receiver for the 1895 variations produced in 45/70, .444 and .450.