My Trap scores are much better when I use three inch shells. I buy primed three inch hulls from BPI and use winchester wads. I have a MEC 600. I load 11/16ths of #9 shot over 14 grains of Alliant 2400. (I have used Alliant 410, H110, IMR 4198, AA#9). I like 2400 best.
Pete
Pete