It should take 2 3/4" rounds, but definately not 3" magnums. If you have any doubts have a smith check it. My Dad carried my Grandfather's 520 as his duty/riot gun into the mid 80s, and took it to a NRA Police Shotgun Instructors course in 1988, the guys nick named him Alvin York. I was issued and carried a personal 870, but to me, that 520 always looked like what a riot gun should look like. mal