303 barrels were built for 173gr flat bottom bullets, they work fine with lighter bullets depending on your loads, wear, etc.
7,62 barrels built for boat tail 145gr bullets, but again will work with heavier and other bullets, again depending on what you load.
Its not the barrel that's the problem it is the action. You can load anything into a case and fire it. Later day 7.62/308 have a higher pressure than what the action was built for,