When I was overseas doghandlers carried the GAU-5a, a stubby ar15, with a short barrel and flash hider and collapsible stock. Stateside it was always the model 15. It was all about controlling your dog. Thanks for the response. The 4 series came out about the time I got out. All the 15s I carried were 2-3, but I don't see or know what the changes were. ⁷Close enough for a nostalgia trip.