The Magpul ACS (Adaptable Carbine/Storage) Stock in Mil-Spec Black (brand part no. MAG370-BLK) is a drop-in replacement buttstock for AR-15/M4 carbines running mil-spec-sized receiver extension tubes. Dual, rear-accessible, water-resistant battery storage tubes plus an integral storage compartment in the butt of the stock give shooters real, usable storage options for spare batteries, a cleaning kit, or other small essentials. Like the popular Magpul CTR, the ACS features an anti-snag release latch to prevent accidental activation, along with a supplemental friction lock system that minimizes excessive stock movement for better weapon stability and accuracy. A 0.30-inch thick rubber butt-pad provides positive shoulder purchase, keeping the stock from slipping even when shooting with body armor or bulky modular gear.

Key Specifications

• Fits standard Mil-Spec AR-15/M4 receiver extension tubes.
• Includes dual water-resistant battery storage tubes, rear-accessible.
• Features an integral storage compartment in the stock’s butt.
• Anti-snag release latch prevents accidental activation.
• Supplemental friction lock system minimizes stock movement.
• 0.30-inch rubber butt-pad for positive shoulder purchase.
• Finished in Mil-Spec black.

Frequently Asked Questions

Does this stock have storage built in? Yes, it includes dual rear-accessible battery storage tubes and an integral compartment in the butt.

Will this fit a commercial-spec buffer tube? No, this version is built for Mil-Spec-sized receiver extension tubes; confirm your tube diameter before ordering.

Does the stock stay stable while shooting with body armor? Yes, the thick rubber butt-pad and friction lock system are designed to provide positive purchase even with bulky gear.

Buy the Magpul ACS Carbine Stock

Order it from our Lubbock, Texas gun shop as soon as it’s available to ship, and add real storage and stability to your AR-15 build.

Shop more from Magpul Industries and browse our full AR braces and stocks selection.