The "76" (although it looks to be in a strange place in your string of proofmarks) likely is the chamber length, and that would be 3". I would not use Hevi-Shot in that gun. If you are waterfowling with it, or are in a nontoxic only area for upland birds, I'd recommend Kent's Tungsten Matrix. Great stuff.
If you're just looking for more range and don't need to use nontox, you might try the 2 3/4" 20ga magnums, 1 1/8 oz shot, usually buffered. They'll give you a pretty good kick in a Bernie Gamecock, but the buffering and the heavier shot charge will give you a denser pattern and a bit more range.
Thanks for the heads up. The heavy loads would be used for coyotes and maybe turkeys. The state land here will not allow rifles with any punch.
Who makes the 2 3/4 magnums?
