The Brownells BRN-180M Lower Receiver is specifically designed to pair up with the BRN-180 Upper Receivers to maximize the full potential of this unique line.
While designed to be fully compatible with Mil-Spec lower receiver parts and triggers the BRN-180M Lower Receiver does away with the traditional receiver extension threads and in their place has a milled in 1913 Picatinny rail section for mounting of stocks or braces such as the line for the Sig Sauer® MCX.
This Lower Receiver is made from billet 7075 T-6 aluminum with a hard-anodized finish, has integral oversized trigger guard, and the unique features of a threaded bolt catch pin and captive set screw for the takedown pin detent spring, both included.
Due to the proprietary design nature of the BRN-180M Lower Receiver it will not function with standard AR-15 upper receivers.
Big Book Catalog, Issue:73, Page:009