The patent-pending Magpul® ACS™ (Adaptable Carbine/Storage – Military 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 CTR™, the ACS™ also features a supplemental friction lock system that eliminates 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 rubber butt-pad which gives positive shoulder purchase to prevent slippage even with body armor or modular gear.
Note: There are two basic types of M4 Carbine Receiver Extensions (buffer tubes): Mil-Spec and Commercial. If you have a Commercial extension on your rifle, make sure to order the soon-to-be released Commercial ACS™ (MAG371). For help identifying which extension is on your rifle, please visit
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