Just saw part of "No Country For Old Men", OK I know it's Hollywood but is a shotgun with a Foster's oilcan size suppresser stuck on it going to work in the real world. I mean more than one shot.
The design for a shotgun silencer is different than one for a solid projectile (rifle, pistol silencers)
Basically it involves porting the barrel and putting an outer tube and baffles over that, so that you can use buckshot/birdshot/slugs without a problem.
But no, a tiny silencer like that wouldn't have reduced sound as shown in the movie. They need to be, in a word, HUGE.
That makes it no more different than any other "silencer" that Hollywood has ever shown; how many times have we seen "the bad guy" screw a suppressor onto a revolver that didn't have enough volume to adequately suppress a .22, let alone the .38 that they were holding (completely aside from the revolver issue, for which I know there are exceptions)?