If onboard storage is the reason you’re after the ACS, this combo gets you there without a separate parts run. The ACS sells as a stock only — no buffer tube, buffer, spring, or hardware — so we’ve bundled the genuine ACS in black (MAG370BLK) with a complete carbine buffer tube assembly. The whole back end of the rifle ships together.
The ACS, short for Adaptable Carbine/Storage, is the storage king of Magpul’s carbine line. It carries two rear-accessible, water-resistant battery tubes plus a separate covered compartment in the butt, so spare CR123A or AA cells, cleaning patches, and small parts all ride on the gun.
A supplemental friction lock (same idea as the CTR) takes the wobble out of the buffer tube fit for a steadier hold, and the streamlined, anti-snag body shields the release latch from getting bumped. A 0.30″ rubber butt-pad keeps it planted against a shoulder or plate carrier, and a fixed cheek piece gives a consistent, repeatable cheek weld.
The buffer tube assembly supplies the recoil hardware: a 6-position mil-spec receiver extension, carbine buffer, recoil spring, castle nut, and end plate, all built to the 1.148″ mil-spec diameter. It drops onto any mil-spec AR-15/M16 lower, 80% lowers included. Finish the build with our lower parts kits, or compare other stocks and buffer tube kits.
Included in this combo:
- Magpul ACS (Adaptable Carbine/Storage) Carbine Mil-Spec Stock — Black (MAG370BLK)
- Mil-spec carbine receiver extension (6-position buffer tube)
- Carbine buffer
- Action / recoil (buffer) spring
- Castle nut
- Receiver end plate
ACS stock specs:
- Drop-in replacement for AR-15/M16 carbines on mil-spec receiver extensions
- Two rear-accessible, water-resistant battery storage tubes
- Separate covered storage compartment in the butt
- Supplemental friction lock minimizes stock movement
- Streamlined, anti-snag profile shields the release latch
- Dual ambidextrous QD sling sockets
- Fixed cheek piece for a consistent cheek weld
- 0.30″ rubber butt-pad; six length-of-pull positions
- M4 length of pull: 11.6″ collapsed, 14.9″ extended; adjustment range 3.3″; max length 8″
- Weight: 14.1 oz; Made in the USA
