Shotguns and US Spec Ops

US Spec Ops:

Sources for images might be (if what you want is balaclava'd troops with
MP5-K or MP5-SD) any Osprey book on the SAS (specifically around the
Iranian
Embassy siege time frame) or similar. 

Another source for more modern type figs might be the Stargate SG-1
website
or fan sites. I'm sure they've got picks of guys with MP5s and American
helmets and combat kit. (Though why they wouldn't take an M4/CAR-15 or
an
M-16, I just can't fathom.... they seem to operate in the bush most of
the
time...). 

Attached Shotguns:

As Los points out, why take a shotgun for close in combat if you have a
bullpup AR? It penetrates better, can fire short bursts if you need some
dispersion, and is easier and lighter to point without the underslung
shotgun, and it is useless against armour. 

If you have the integal GL, you could fire the breaching round he
mentioned
_and_ probably cannister/flechette too! With such a GL (which I would
say
holds 3-5 rounds), you can fire a variety of ammo by loading the mag
accordingly.

I assume an underslung shotgun (firing flechettes, if anything) probably
only holds 4 or at most 5 rounds, given the constricted length for a
magazine for it. 

Take the GL, give it a shotgun loadout if need be. Far more multirole
capable. Range probably between 250-400m if current tech is a guideline.
And
with a capacity to deploy armour piercing, HE dual purpose, cannister,
illum, maybe some kind of EMP, beanbag, breaching, and other oddball