Made in the USA The Magpul ACS (Adaptable Carbine/Storage) Mil-Spec Model is a drop-in replacement buttstock for AR15/M4 carbines using mil-spec sized receiver extension tubes. Dual rear accessible water-resistant battery storage tubes and an integral storage compartment in the butt of the stock provides multiple storage options. The ACS comes standard with a 0.30″ thick rubber butt-pad which provides positive shoulder purchase to prevent slippage even with body armor or modular gear.