No, I mean in real life, how the hell do you silence a shotgun? The length of the suppressor is directly related to the aperture size of the barrel. A twelve gauge shell would require a suppressor so large as to make the shotgun unbalanced and unwieldy, maybe even longer than the gun itself. Further, the sound of the gun chambering a round is a non-trival noise that can often be much more audible than the firing sound on a suppressed weapon. A suppressor gives no advantage of it is accompanied by a loud “ca-chunk” sound as the next shot is readied, and large size of the rounds in a shotgun almost always ensure a load chambering. Actually, that is considered an advantage as far as home-defense users are concerned, as the sound of a shotgun chambering is distinctively intimidating.

via How is the silenced SPAS-12? – Tom Clancy’s Splinter Cell: Conviction Message Board for Xbox 360 – GameFAQs.