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The .338 ARC is one of the more interesting cartridges to come along in recent years. Hornady designed it around the 6.5 Grendel case, necked up to take a .338-caliber bullet, which means it fits in a standard AR-15 magazine well and runs in an AR-15 lower receiver while delivering energy levels that make .300 Blackout subsonic look modest by comparison. The subsonic load runs a 307-grain bullet and the supersonic 175-grain option reaches out past 200 yards with authority. CMMG recognized early on what this cartridge could do in a short-barreled PDW configuration, and the Banshee MK4 is the result.
The upper receiver is Mk4 billet 6061-T6 aluminum while the lower is forged 7075-T6, a combination that gets you the best of both worlds in terms of precise fitment and structural toughness. The 10.5-inch barrel is 4140 chrome-moly with a nitride finish and a 1:8 twist rate, threaded 5/8×24 so you can run your suppressor of choice or swap the included Zeroed linear compensator for something else. The EML9 handguard wraps the barrel with full-length M-LOK slots on both sides and the bottom, plus M-LOK between the top Picatinny sections, so there's no shortage of real estate for accessories. All controls are CMMG's Zeroed parts, including an ambidextrous charging handle, ambi mag catch, extended mag release, and pistol grip. Everything ships ready to mount an optic.
The RipBrace is one of those features that sounds like a gimmick until you use one. CMMG's Fastback Technology means there are no levers to press or tabs to fiddle with. You just pull the brace rearward and it snaps to your pre-set length thanks to the P3 Personal Position Preset system, which uses an indexing screw to lock in your preferred length of pull so it goes to the same spot every time. For a firearm this capable in this compact of a package, that kind of fast, repeatable deployment actually matters. The Banshee MK4 is backed by CMMG's Lifetime Quality Guarantee and is made in the USA.
The .338 ARC uses a 6.5 Grendel-based case necked up to a .338-caliber bullet, which gives it roughly 1.5 times the muzzle energy of comparable .300 Blackout subsonic loads while still running in a standard AR-15 lower receiver. The subsonic 307-grain load and a supersonic 175-grain option give you real flexibility depending on whether you're running a suppressor or shooting unsuppressed. It's a meaningfully more capable cartridge than .300 BLK in a pistol format, not just a marginal upgrade.
The RipBrace uses CMMG's Fastback Technology, which means you simply pull the brace straight back to extend it. There are no levers to press or detents to clear. The P3 (Personal Position Preset) system uses an indexing screw so you can dial in your preferred length of pull once, and it returns to that exact position every time you deploy it.
Yes. The 10.5-inch barrel is threaded 5/8×24 and includes a CMMG Zeroed linear compensator that can be removed in favor of a suppressor. The .338 ARC cartridge was specifically engineered with suppressed shooting in mind, and the pistol-length gas system on the Banshee MK4 is tuned to run reliably in that configuration.
The billet 6061-T6 upper receiver is machined from a solid block of aluminum, which allows for tighter tolerances and more refined geometry around the barrel extension and handguard interface. The forged 7075-T6 lower is made from a stronger aluminum alloy that handles the stress of repeated use exceptionally well. Together they're a well-matched pairing that balances precision fit with durability.
The Banshee MK4 in .338 ARC ships with one 10-round CMMG .338 ARC magazine. The .338 ARC uses a 6.5 Grendel-compatible bolt face and its own magazine format, so standard AR-15 magazines are not compatible. CMMG and other sources list the included magazine as a 10-round.
The Banshee MK4 ships optics-ready with a Picatinny rail on the upper receiver, so it will accept any standard AR-compatible optic. Given the short barrel and intended use at defensive and close-to-mid range distances, a red dot or low-power variable optic (LPVO) in the 1-4x or 1-6x range are the most practical choices. The EML9 handguard also has a top Picatinny section for offset or backup sighting options.
| UPC | 840442506582 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | 34A390F-AB |
| Action | |
| Barrel Length | 10.5'' |
| Caliber/Gauge | .338 ARC |
| Capacity | 30 |
| Color | Black |
| Length | 3.5'' |
| Magazine Included | 1 x 30-Round |
| Model | |
| Product Type | AR |
| Safety | Ambidextrous |
| Shipping Weight | 9.505 |
| Sights | Optics Ready |
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