BudsGunShop.com - Lower receiver...metal or polymer

Richard, 7075-T6 hard-coat anodized aluminum. See all specs here-- ruger.com/products/ar556/specSheets/8500.html

Richard, it is made of Metal (7075-T6 Aluminum) - ((Specifications and Features)): - Ruger AR-556 8500 - AR-15 Semi Automatic Rifle - 5.56 NATO accepts .223 Remington - 30 Rounds - 16.1" Cold Hammer Forged Barrel - 1:8" Twist - Muzzle Threaded 1/2-28 TPI - Carbine Length Gas System - Mil-Spec Diameter Buffer Tube - Six Position Collapsible Stock - Overall length 35.5" - Weight 6.5 lbs - Black.

Metal. 7075-T6 hard-coat anodized aluminum forgings.

Hi,
The lower receiver is made from 7075-T6 aluminum. Cheers.