Ledbetter, glad you had fun. Scatterguns is a hoot!
For clays, there are no equipment restrictions... the rangemaster was just trying to tell you that a short-barrelled riot gun is no good for trap or skeet. Yah right, sez me. Best round I ever did was with my M500, 18" cylinder bore, pistol grips at both ends.
The most common gun for clays is an over/under with 28"+ barrels and chokes that are tighter than... uh, you get the picture. Makes the other shooters indignant when they see a newbie with a room-broom busting clays.