AR6460 = regulation enforcement semi-car carbine with retractable inventory and 16 inch very long barrel and bayonet lug I have never decided on a flat prime or A1 (without FA and deflector). I'm pondering a 16" flattop, and also a 10.5" with have handle like yours. I've a few Aero https://colt-10-5-upper42851.amoblog.com/the-5-second-trick-for-colt-smg-upper-48327679