1 1/2" bore - that's just under a 1 pounder for a round ball gun/canon (1.671" = 16 ounce ball)

The charge, iirc from something I read decades ago, was 1 pound of powder and 3 pounds of #1 shot. Most killed (USA) was 128 or 129 ducks at from 100 out to 120yards (flock) with one shot.

The story/article told of holding 4' above the surface to allow for drop, shot cloud spread and the ducks taking off with the smoke cloud, before the shot got there, then rising up into the shot cloud. The first pellets would strike probably at 90 yards or so and out to 130yards. #1 shot was preferred as it was plenty for ducks. Geese would likely see larger shot, perhaps B or BB.