I often get a shotgun as heavy weapon for non-combat characters (longarms 1 with shotgun specialisation and you're not that bad with them for only 6BP). It's easier to get, isn't as suspicious as automatic riffles, and I've never had the short range being an issue (in fact, for long range combat we mostly use the spirits the mage summons).
I mostly take the Enfield AS-7 with the 24 bullet drum and the following mods: Folding Stock (Powered), Foregrip, Personalized Grip, Smartgun System, Sling. Makes it a very good weapon for short range combat for the non-combat specialist. With the drum, the foregrip and the stock extended I feel it looks a bit like a heavy duty tommy gun, which is good enough just for coolness factor.
I'd recommend the AA-16. Stock FA capability, 32 round drum, and it's the only shotgun with a Gas Vent system, which gives it +2 Recoil Compensation,
and it only uses 10 rounds for Suppressive Fire when using flechette.
Plus, it's the grandchild of the AA-12 used in CanRay's link.

Also, as always when the subject of flechettes comes up, I'll advise checking to see if your GM will let you replace regular Flechette ammo with AP-Flechette. Some GMs consider them the same thing when a weapon calls for flechettes, others get their knickers in a twist about the difference, so it's best to get that cleared up right away.
If your GM is cool with it, though, +0 AP vs +5 AP is so worth the -20% range... especially if you compensate for part of it with the Extended Barrel.