I just got a used sb2? frame that was a 3006 originally. Question, when looking at front of frame, where forearm meets it. It looks like a piece of channel with a addition to the inside of frame. Is this just the way its made or what. My ss1 frame is solid all the way accross this surface while the sb2 is recessed with about a eighth inch wall exterior. Also has anyone had a sb2 factory fitted with a 17hmr barrel. will they do that?