Rise Armament Lower Parts AR-15 KitThe Lower Parts Kit features all of the working components of a lower receiver, minus the trigger. It is compatible with mil spec AR 15s. OVERVIEW The RISE Armament 20 piece AR 15 Lower Parts Kit has all the pieces you need to assemble a lower receiver with quality parts. Most of the mil spec parts featured in the RISE AR 15 Lower Parts Kit are made of the industry standard 8620 steel. The 8620 carbon steel is a full up alloy of nickel, chromium,