I have three Parker hammerguns- two lifters and a top lever and none of them have " proof marks ". I don't remember American shotguns having proof marks. Maybe I'm wrong and not just looking in the right spot. Also looked at my two Remington hammerguns and could find no proof marks. One of my Parker lifters has a strange type of barrel. It appears that one piece of metal about an inch wide was wraped around a mandrel and forge welded. I wouldn't call it damascus twist because it's only one type of material, not iron and steel. I've never seen mention of this anywhere. Paul