0NachoMahma 11 years ago ReplyUpvote. ROFLMAO! That is hilarious. . What is that piece directly below where the tail stock joins the lower receiver? I don't have one of those on my AR-15A1. Collapsible handgrip? . Great little guns, ain't they? I've killed hundreds of aluminum cans with mine. Mine still has the collapsible stock, flash suppressor/muzzle brake, and unmodded magazines - guess I better stay out of California. heehee . Don't forget your earplugs!