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?
Depending on the load, a couple of hundred meters is possible
Depends on the gauge, load and power level. At least a few hundred yards.
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.
depends on the bird
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.
I don't understand the question. Were you shot in the back with a .22 and wonder how far it could have gone?
Shotgun by far
Depends. Bird shot, buck shot, or slugs? Length of barrel? Size of shell? for most birdshot, about 35 yards, most buckshot, about 45 yards, slugs, about 100-125 yards accurately. Larger pellets can travel about 700 yards, but not effectively.
about 36km
Muzzle loader or centerfire?
30-300 yards depending on load, angle of fire, etc..