The MagpulA(R) ACS is designed to be a drop in replacement carbine stock body. This is a stock only. The Magpul ACS (Adaptive Carbine/Storage) is a drop-in replacement for the standard M4 stock body, offering a comfortable sloping cheek weld, integral storage compartment, anodized aluminum strike plate, battery storage tubes, and a friction locking mechanism to eliminate excessive movement. INTERNAL STORAGE COMPARTMENT - The ACS features an internal storage compartment large enough for basic weapon maintenance/cleaning supplies, spare parts, or other small items. BATTERY STORAGE TUBES - The ACS has two battery tubes, allowing for storage of six (6) CR123 or four (4) AA batteries in total. Batteries are accessible via rubber caps without removing or adjusting the stock. FRICTION LOCK - Similar to the Magpul CTR stock, the ACS features a friction locking mechanism to secure the stock and eliminate excess wobble and movement. Mounts on Mil-Spec AR15/M16 carbine receiver extention (buffer tube) (including; Colt, BCMA(R), CMT, LMT, Vltor, Stag) Color: BLACK