Just an estimate here.

If you are shooting parallel to the ground from the shoulder, standing, your barrel will be approximately 5 feet off the ground. We'll assume no "Kentucky windage" for this equation.

Brenneke 12 gauge, 3-inch Gold Magnum lists 1.5" drop at 100 yards. Probobly something like 18" drop at 200 yards (my estimate). Probobly in the dirt by 300/350 yards.

If ya aimed at the sky a bit I don't think 500 yards would be out of question, by accuracy certainly would be.

Uncle Matt (in IL)