Chad Dickinson

I bought a Super Vinci last spring. LOVE the gun. Shoots great. One thing I still can't figure out is why I can only get 3, 3 inch shells in it? Let alone 3 1/2 inch shells. Benelli's site says standard configuration is 3+1. Only time I can get 3+1 is if I'm shooting 2 3/4 inch shells. Is this right? Or what am I doing wrong to get the additional shell in there? Is the magazine plug come installed? I never did see a plug included with my gun. Thanks. Chad