Complete mil-spec receiver-extension package for AR-15 lowers built in 5.56 NATO, .223 Rem, or 300 Blackout. Everything you need to run a collapsible carbine stock, in one kit.

Includes:

• Six-position buffer tube, mil-spec 1.148" diameter, T6 aluminum, Type III Class II hard-coat anodized
• Carbine recoil spring (standard length)
• Steel castle nut, staked-ready
• Standard steel end plate
• 3.0 oz carbine buffer weight

Fitment: mil-spec (not commercial-diameter). Any mil-spec 6-position collapsible stock — Magpul MOE, B5 Systems SOPMOD, Sopmod-style, PDW, etc. — will slide on. Rifles chambered in 5.56 NATO, .223 Rem, and 300 BLK all run this weight; heavier calibers or short-stroke builds may want to swap the buffer for a heavier H1/H2.

Torque the castle nut to spec and stake against the end plate before running the rifle hot — an unstaked castle nut will walk loose under recoil.