John, that's a trick statement he made. Qualified by what one can pick off the shelves at Wally World. Commercial 12 gauge loads may out shoot commercial 10 ga. loads because the ammo companies stopped developing the 10 and devoted development to the 3.5" 12. There are some niche companies who have hotter ammo than any 12. Handloads can also take advantage of the volume of the 10 ga. 3.5" hull and outshoot the piss out of any 12 gauge. Take a look at the copper plated lead shot in 10 ga. 3 oz of shot at 1200 fps. Gil
http://www.nitrocompany.com/ammunition.html#CopperTable