The Brownells XM16E1 lower receiver is a replica of the receiver on the original XM16E1 rifles developed for the U.S. Army in the 1960s. We worked with the folks at Nodak Spud to produce a receiver that replicates the exact contours and "partial fence" configuration of the original XM16E1, making it perfect for a Retro build replicating the early Army M16s (see Gun Tech Note™ below fore details) Each of our XM16E1 lower receivers starts life as a 7075 T6 aluminum forging that is precision-machined to final dimensions before receiving a gray hardcoat anodized finish that gives the best match to the color of the originals. Simple, engraved markings on this lower won’t detract from the period look and include the following: Model: XBRN16E1 Cal: 5.56mm Mfg: Brownells Inc. Current-production AR-15 components will work perfectly with the Brownells XM16E1 lower receiver. NOTE: FFL required for purchase. Brownells Gun Tech™ Note: The original XM16E1 lower receiver was developed for the "improved" M16 rifles produced by Colt Manufacturing for the U.S. Army from 1964 through 1967. These receivers were found on the first M16 rifles issued to the troops in Vietnam, before the arrival of the M16A1. XM16E1 lowers were used on the first M16s with the forward assist, as well as various early M16 carbines. Features specific to the Brownells XBRN16E1 lower that make it a close replica of the originals include the proper front takedown lug profile and the contour of the metal surrounding the receiver extension. Also, the XM16E1 lower was the first with the "partial fence" above the magazine release and just below the ejection port cover. Most forged AR-15 "carry handle" lower receivers produced today have the A2 profile, which is incorrect for reproductions of early M16 rifles. This XM16E1 lower is the correct receiver for building reproductions of the following rifles: XM16E1 Model 604 Model 605 Carbine Model 606 Model 607 Carbine Model 608 Survival Carbine Model 609 "XM177E1" Carbine Model 610 "XM177" Carbine