AR6460 = regulation enforcement semi-car carbine with retractable inventory and 16 inch extended barrel and bayonet lug It's an ordinary FSB and no I'd no complications sighting it in. I originally created it which has a DPMS A2 upper receiver just before getting the 604 receiver. I had no problems https://garrettqcocp.amoblog.com/top-latest-five-colt-10-5-inch-9mm-smg-upper-receiver-assembly-urban-news-48345367