I dont think it is 303 as i just took a round of 303 and it with in the rifle as it was made for it, I dont have any of my reloading books in the house right now so 30-30 might be about right but 303 is almost if not the same length at this point and my 30-40 rounds are not in the house eiths to compair with, if I remember i will go pull a round of each and check them for length