The 1903 had sights mounted on the barrel, the 03A3s had peep sights in the rear, had a LOT of shortcuts done for manufacturing purposes (including the infamous 2 groove barrels, 1903s had four groove barrels), and some other minor changes. 03A3s had parkerized finishes, the 1903s were blued, stuff like that. The 1903s were a lot smoother to operate, too, but as a practical matter, the 03A3s were good rifles, just not as "finished" as the older brothers.