The patent-pending Magpul ACS (Adaptable Carbine/Storage) ? Mil-Spec Model is a drop-in replacement butt-stock for AR15/M16 carbines using mil-spec sized receiver extension tubes. A streamlined anti-snag profile shields the release latch to prevent accidental activation and the extra-power lock mechanism uses a premium chrome-silicon spring to avert auto-collapse failure by resisting spring relaxation. Similar to the Magpul CTR? the ACS also features a supplemental friction lock system that minimizes wobble* for enhanced weapon stability and accuracy. 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.