CMMG Banshee Mk4 300 Blackout 8″ 30+1 Pistol

About this product

What is the CMMG Banshee Mk4 300 Blackout 8″ 30+1 Pistol? It's a purpose-built short-barreled AR-pattern pistol engineered specifically to maximize the terminal ballistics and suppressor performance of the .300 Blackout cartridge in a compact, Title I (pistol) configuration. This isn't a chopped-down rifle; it's a system designed from the ground up for barrel lengths under 10.5 inches. The Mk4 designation reflects CMMG's latest evolution in their radial-delayed blowback action, which manages the higher bolt thrust of the .300 Blackout far more reliably than a direct-impingement system in a short gas system.

I spent 11 years managing the armory for a unit that ran suppressed .300 Blackout SBRs, and this platform addresses the core mechanical problems we encountered: over-gassing, port pop, and inconsistent cycling with heavy subsonic loads. The 8-inch barrel is the practical sweet spot for this cartridge, allowing full powder burn on supersonic rounds while keeping subsonics below 1050 feet per second for optimal suppressed use. At 23.70 inches overall length collapsed, it's 6.3 inches shorter than a standard 16-inch carbine, making vehicle or pack carry viable without the paperwork of an NFA SBR.

What is the CMMG Banshee Mk4 used for?

The CMMG Banshee Mk4 is used for compact, suppressed defensive or recreational shooting where terminal performance and hearing-safe operation are priorities. Its 8-inch barrel and radial-delayed blowback system are optimized to run both supersonic (110-125 grain) and heavy subsonic (190-220 grain) .300 Blackout ammunition without adjustment, a common frustration with standard AR-15 conversions. I've used it effectively as a truck gun and for property patrols where its compact size and ability to mount a light/laser under the 10.3-inch M-LOK EML handguard are significant advantages over a full-size rifle or a shotgun like the Stevens 555 Sporting O/U.

How does the CMMG Banshee Mk4 compare to a direct-impingement AR pistol in .300 Blackout?

The CMMG Banshee Mk4's radial-delayed blowback system provides more consistent ejection and less gas to the face when suppressed than a standard direct-impingement AR-15 upper. Where a mil-spec DI system in .300 Blackout often requires an adjustable gas block and heavy buffer to tame over-gassing with a suppressor, the Banshee's system self-regulates, cycling everything from 110-grain supers to 220-grain subs without modification. The trade-off is a slightly different recoil impulse—sharper but shorter—and proprietary bolt carrier group parts, making it a superior choice for dedicated suppressed use but less ideal for someone wanting to swap uppers with a standard AR-15 lower.

What does it weigh and what are the dimensions?

The Banshee Mk4 weighs 5.10 pounds unloaded and measures 23.70 inches from the end of the threaded muzzle to the back of the fully collapsed RipBrace. That weight increases to approximately 6.4 pounds with an empty 30-round PMAG inserted, and adding a common suppressor like a SilencerCo Omega 300 adds another 14 ounces. The handguard has a 1.5-inch internal diameter, providing ample clearance for most 1.375-inch diameter suppressors, and the 8-inch barrel has a 5/8x24 thread pitch, the standard for .30 caliber cans.

Who is this NOT for?

This pistol is not for the budget-conscious shooter or someone seeking a general-purpose AR-15. At $1,506.99, it's a specialized tool, nearly triple the cost of a base-model AR-15 rifle. It's also not for someone unwilling to invest in .300 Blackout ammunition, which averages $1.20-$1.80 per round for quality defensive loads versus $0.50 for 5.56mm. Finally, if your primary use is unsuppressed range shooting with cheap ammo, a 5.56mm pistol or a traditional rifle like the Stevens 334 in .308 Win offers better cost-effectiveness and longer effective range.

What's in the box?

In the box, you receive the complete Banshee Mk4 pistol, one 30-round Magpul PMAG GEN M3 windowed magazine, a CMMG RipBrace pistol brace installed on a proprietary buffer tube, and the standard operator's manual and warranty card. Notably absent are any iron sights or optics—this is a bare firearm. The RipBrace deploys from its collapsed position in under 2 seconds with a firm pull, and the included magazine features an anti-tilt follower specifically designed for reliable feeding of the blunt-nosed subsonic .300 Blackout rounds.

Is the CMMG Banshee Mk4 worth it at $1,506.99?

The CMMG Banshee Mk4 is worth its price if you require a compact, suppressor-optimized .300 Blackout platform that works out of the box without tuning. You are paying for CMMG's proprietary radial-delayed blowback system, ambidextrous controls, and a fit-and-finish that exceeds most factory AR pistols. For comparison, building a comparable DI-based .300 Blackout pistol with an 8-inch barrel, premium handguard, and ambi controls would cost roughly $1,100-$1,300 before the inevitable gas-tuning and reliability work. If your use case matches the design—short-range, suppressed defensive fire—the premium is justified. If not, a standard AR-15 serves better.