For those who are good at smuggling, also consider the non-Canadian (non-gibbled) variant of the FN P90:

• This is a bullpup semi automatic that works exceptionally well in the urban environment.
• The short barrel variety can be equally as mobile inside of structures as a sawed-off shotgun, if not more so. Plus, far less telegraphing of your presence (muzzle precession) as you go around corners compared to non-bullpup long guns.
• Each of its 3 magazines can hold 50 rounds, and two magazines can be stored inside the shoulder stock.
• The brass is ejected straight downwards, and the grip is totally ambidextrous, which means it can be handed off between righties and lefties with zero mods needed. No hot brass to the face simply because the prior user was differently-handed.
• The UN ammo that is standard for it has limited range, which means it is less likely to have secondary down range casualties, yet still comes in a wide variety of slug types including body-armour-piercing.

If you want to see this weapon in use, pick up any season of Stargate SG1.

Downside is that the ammo isn’t cheap. In fact, it’s stupidly expensive. But the P90 is also used by many U.S. divisions such as the Secret Service, so the ammo can be “acquired”.