This is the “forward” component of the Lower Receiver in the Windham Weaponry Multi-Caliber System, and slides and locks onto the MCS Lower. With this Magazine Well, you’ll be able to utilize magazines for .223/5.56mm; .300 Blackout, 7.62x39mm Calibers as well as any other caliber that utilizes an AR pattern magazine. For 7.62, the magazines must be AR pattern. CNC machined from 7075 T6 aluminum forgings, they are bead blasted and final finished in Hardcoat Black Anodize. Made in the USA.