Depends on the gauge, load and power level. At least a few hundred yards.
30-300 yards depending on load, angle of fire, etc..
Depending on the load, a couple of hundred meters is possible
a 12 gauge shotgun can shoot about 30 yards accuracy
Depends on projectile size. # 9 shot probably won't travel 200 yards, but 00 or 000 buckshot or a deer slug might travel over a mile.
Depends on the load. 30-300 yards
In excess of 50 m
Are you interested in knowing how far a 12 gauge slug will travel, or are you looking for the distance various loads of shot will travel?
Shotgun by far
That will depend on the size of the shot, and not the gauge. Fired across level ground with the largest buckshot, a shotgun has a maximum range of between 600 and 700 yards. Not a usable range- just the furthest that shot will travel.
The shot will travel a couple of hundred yards, easily.
It would depend on the powder charge, weight of load, and aerodynamics of the load (Solid slug, shot, etc)