If it was me I would get a 12 gauge 3.5". If you are out duck hunting with your friends and run out of shells you can bum some shells from them. If they only have 3.5" you are safe. But if you buy a 3" chamber you are up the creek with out a paddle. I love my Benelli SBE II. aslo not many people around here use a 10 gauge for duck hunting.