I have a Gen 1 model 17 with the model number starting prefix AT. I have the.572 inch Barrel and my Barrel and my slide and frame all have matching numbers. All my parts are black inside. My gun looks to be 100% Original. How old of a gun do you have to get before you run into a pencil barrel. I did do a few searches on this bit of info and tried to use an old post to ask this question before I created a new post.