An 80 percent lower’s a partially machined lower receiver for AR-15 or AR-10 rifles, not yet considered a firearm by law. It requires additional milling to become functional. Once completed, it works with upper receivers, lower parts kits, buffer tubes, stocks, magazines, and other standard AR-15 or AR-10 components. The 80 percent lower allows DIY builders to customize and assemble their own rifles, offering compatibility with a wide range of parts for hunting, target shooting, and tactical builds.