What are you going to use it for? I have a .410 and I shoot 3" brenneke slugs. It's great for deers at close range(35 yards or less). Also great for coyotes and foxes. I don't think it would hurt or foulyour barrel more or less by using 2 1/2" slugs but I strongly recommend the 3" because being a small caliber already you'll want more bang out of it.