For years I carried an electronic fish scale and weighed bobcats and coyotes but I don't remember ever weighing a coon for some reason. Or a skunk, possum, or armadillo. My average coon size would be about - average. 
Guessing somewhere in the teens, maybe a 15-pound average with a few going a little over 20 pounds. Most of those shot with the shotgun are within 30 yards. This Remington load from a factory full choke is the absolute hammer all-around shotgun coon load in my opinion. You can shoot them from the top of tall trees with this load if necessary.
Buy Nitro Magnum, 12 Gauge, 2 Shot, 2-3/4 in, 1 1/2 oz, 1260 fps Ammo | Remington
