Again, for my senior project, and also a small game design company in Poland.
Shotguns are a type of weapon that hasn't changed much in the near future. The rail and gauss principle does not work as well for shotguns as it does for pistols and rifles.
Top: Royal Plutonian Ballistics Model 1, 12 gauge full auto compact shotgun with pistol grip. A simple, old, and widely available model. It comes in many MANY variations. A favorite among criminals and soldiers alike for it's legendary reliability and ease of use. This particular model has an aftermarket heat shield, tactical barrel, and the stock has been detached.
Middle: Umbra Armory "Grizzly Bear" Twin 20 gauge full auto shotgun with folding butt stock, bipod, and 2 X 20 round box magazine. An interesting departure from convention this weapon is tough to stand against for long. Designers chose to use the smaller 20 gauge round to minimize recoil fatigue from the shear amount of lead this thing throws down range. The unique box magazine has two separate coils and feeders, the right feeds to the bottom barrel, while the left feeds the top. Very effective for holding combat lines defensively.
Bottom: Nottingham Research Quad-Matic Charged Particle Shotgun. Probably the most exciting advance in shotgun technology is the four barreled Quad-Matic. Instead of using the traditional lead round, this gun fires bursts of charged heavy particles. It can be set to fire all the barrels at once, or only two of them, doubling the ammo cap in exchanged for slightly less power. This model has a heartbeat detection radar mounted above the grip, and features the desert camo of the Venusian security force.
EDIT: Fixed the heat shield on the top one.