The MEGA Forged Lower Receiver comes stripped and ready for your next custom AR build. ZEV starts with high-quality 7075 T6 aluminum forgings and machines them to exceed mil-spec dimensions held to ±.001? tolerances, giving you maximum compatibility with mil-spec and aftermarket parts and accessories. The MEGA Forged Lower Receiver offers superb strength and versatility for building an AR-15 configured exactly the way you want it.Inside diameter of barrel extension is purposely undersized for tighter fit and accuracy.