I prefer a 460 Weatherby...the muzzle blast usully shatters the clay...

Another reason I believe a lot of shooters are using the 20 AND28 gauges for sporting clays is the gun itself. Most of the guns in these gauges are scaled down versions of the 12 ga and are lighter and quicker and less recoil for recovery for the second shot. This said, when I used to shoot clays, I used a Bwg. Citori O/U 12 ga with Invector chokes. For most stages I had skeet/skeet or skeet/IC chokes installed.

Keep in mind.. Your not trying to down a bird.. Your just trying to break a piece of clay which a single bb can and will do.. There is no need for a shoulder pounding 12 guage. The gun will make more of a difference on how you shoot that the guage will..