- Ruger's AR Lower Receiver is a stripped AR-15 pattern lower receiver machined from 7075-T6 forgings with a hardcoat anodized finish. This AR Lower is machined to mil-spec dimensions - including a full-cut fire control pocket and broached magwell - ensuring that your build goes together smoothly. Plus, when your firearm is complete, adjust the included tension screw to eliminate any play between the upper and lower receivers