Having worked at Winchester/US repeating ARMS and Connecticut Shotgun I can tell you this is a very common problem. They have two very good gunsmiths there that work on these and when I used to work with Bill Smith who used to be head of the custom shop at Winchester had always came down to one problem interference, and it usually lies with the cocking arms, slowing the hammer fall down into the fore end that said a lot easier than actually repairing it without chewing everything up when I worked at both places, this was a common ailment that came in weekly and we would shoot them right out the back door at Winchester. Connecticut Shotgun was a little more sophisticated. They had a shooting facility and indoor shooting Tubes Where you could really test the gun. Hope that helps.
