HDM-A2 15 ARCA Rail
15.0 in. free-float ARCA-Swiss handguard for AR-15 uppers. Suits a 16–18 in. barrel on a mid-length or rifle gas system. Continuous top rail, ARCA underside, no barrel-nut timing.
Limit 5 per order.
Part no. CMT-HDMA2-150
The HDM-A2 15 ARCA Rail is a free-float HDM-A2 handguard machined from billet aluminum and finished in black Type III hardcoat. It carries a continuous MIL-STD-1913 top rail that indexes flush with a flat-top upper, and an integrated ARCA-Swiss dovetail along the bottom, plus M-LOK at 3, 6 and 9 o'clock.
CMT's barrel nut does not have to be timed. There is no shim stack to chase and no clocking the nut to clear the gas tube — torque the nut, slide the rail on, and clamp it. That removes the single most common source of a canted rail and lets the same nut come back off for barrel work without a fight.
Fitment
- Mil-spec AR-15 flat-top upper receiver
- Intended for a 16–18 in. barrel running a mid-length or rifle-length gas system
- Clears low-profile gas blocks up to .750 in. journal diameter
- Will not clear a standard A2 front sight base or a clamp-on gas block with an oversized body
In the box
- HDM-A2 15 ARCA Rail
- CMT barrel nut
- Clamp hardware and wrench flats sized for a standard armorer's wrench
Installation. Fit and torque the barrel nut to the value in the instructions with the upper in a proper vise block and reaction rod. Confirm the gas tube passes through the nut without contact before clamping the rail, and verify gas-block alignment before the first live round. If you are not equipped to torque a barrel nut, have a qualified gunsmith install it.
| Platform | AR-15 |
|---|---|
| Rail length | 15.0 in. |
| Series | HDM-A2 |
| Attachment | ARCA |
| Top rail | Continuous MIL-STD-1913 |
| Barrel nut | CMT proprietary — no timing, no shims |
| Barrel length | 16–18 in. |
| Gas system | Mid-length or rifle |
| Gas block clearance | Low-profile, up to .750 in. |
| Material | Billet aluminum |
| Finish | Type III hardcoat anodize (MIL-A-8625 Type III, Class 2), black |
| Origin | Machined in Tennessee, USA |