The Magpul ACS™ (Adaptive Carbine/Storage) fits the standard Mil. Spec. buffer tube and offers a comfortable sloping cheek weld, integral storage compartment, anodized aluminum strike plate, battery storage tubes, a friction locking mechanism to eliminate excessive movement, and optional dual-side QD sling mount.
 
The ACS™ storage features include an internal storage compartment large enough for basic weapon maintenance/cleaning supplies, spare parts, or other small items. The ACS™ also includes two battery tubes, allowing for storage of six CR123 or four AA batteries in total. Batteries are accessible via rubber caps without removing or adjusting the stock.