I'm sorry but the gun is not an older fixed choke gun as described in Chuck Hawk's article. The gun is a waterfowl gun that came on the market with the advent of steel shot and the barrel was designed to shoot the steel. I believe that Chuck Hawks is describing the gun barrels of guns that are pre steel shot.
Also, the receiver of my gun is stamped 3" Magnum, something I don't think you find on other 870's. This is a waterfowl gun, this is not the standard model 870. I believe I bought it the first year it was out.