Now there's no denyin' that if yer talkin' about sheer firepower, two barrels hurts a lot more than one. As to whether it hurts twice as much, I'm not so sure. As far as I kin tell the double-barrel does NOT inflict twice the damage of the single barrel shotgun. Mebbe it's harder to hit dead on with both barrels at once rather than with a single barrel, I dunno. Still, if you wanna run up to someone and point-blank 'em right in the face you should use both barrels. The double also has slightly better range than the single. So far away or close up the double holds the edge.

However, in a sustained gunbattle I'd rather use the single barrel shotgun. Why? 'Cause it's faster. A lot faster. It also doesn't waste as much ammo. But speed is the main factor. Speed kills! If you can shoot faster you can inflict more damage, take advantage of more open shots, and keep yer opponent off balance more effectively. Sure with the double you can fire off two single shots before havin' ta reload, but I think it's faster ta shoot, reload, shoot, reload with the single barrel. Or mebbe I'm just not good with the double...