Ok .46 since you're a fellow gun nut what did the pump-action look like to you?(I can't watch videos at all on this computer it has a 1ghz processor)
The most characteristic feature on the pump shotgun is that the magazine protrudes from where it's mounted to the underside of the barrel by quite a bit. I actually looked through all my shotgun books and no shotgun I could find IRL had a mag that size (I'd say it's a standard 4-5 shot mag) with the mag sticking out quite so much. Other than that, It seems to look like any newer (1920's and up) pump shotgun. It is cleary not an Ithaca 37/Remington 17Remington 31/Browning BPS, since those are bottom ejecting and this gun is side ejecting. Josh pretty much said it's just a generic gun, not modeled after anything particular. The receiver, barrel and fore grip look exactly like the shotgun we saw earlier with the drum mag. I believe that's a mod for this one. The only pump shotgun I can think of off the top of my head that uses magazines like that drum is the Baikal. I've seen them with 5 and 10 round box mags, and making a drum would be no problem.
You just got http://4.bp.blogspot.com/_tNRAa-BYU7M/Ru7zpQTKSYI/AAAAAAAAADw/nz9gMP7T3zU/s1600/ninja_tux.jpg
EDIT:You ninja'd my post of you being ninja'd that's quite a confusing statement.
Swirling Ninjas.
Did you notice if the shotgun has a stock, I could not tell because he was shooting from the hip. I ask this because the riot shotgun and this gun may be different weopons( the riot has a pistol grip), one in 12 gauge and the other in 20 maybe.
The shotgun appeared to have a full stock. Not an English style, like my Auto-5, but the more common and modern "pistol grip" or "half pistol grip" style of full stock. Not a pistol grip lke the M16, but a regular rifle stock pistol grip at the waist like most modern rifles/shotguns.