Straight from Remington
http://www.remington.com/product-families/firearms/shotgun-families/autoloading-model-sp-10.aspx

For serious extended-range shotgunners, there’s only one choice. The Model SP-10.™ Its 10-gauge bore produces significantly superior patterns and less felt recoil than any 12-gauge, 3 1/2" gun out there. And like all Remington shotguns, it excels in the most extreme hunting conditions. It features a corrosion-resistant system, in which the cylinder – not the piston – moves, helping dampen recoil. It’s the only shotgun worthy of the ultimate 3 1/2" bird-leveling payload – the 10 gauge.