The patent-pending Magpul ACS (Adaptable Carbine/Storage) – Mil-Spec Model is a drop-in replacement butt-stock for carbines using mil-spec 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.
NOTE: There are two basic sizes of M4 Carbine receiver extensions (buffer tubes): mil-spec and commercial-spec. This is for the Mil-spec.