CMMG Banshee 300 Complete Upper Assembly (9mm) - 8" Barrel - M-LOK Handguard

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BANSHEE 300 (9mm) Upper


Convert your standard .223/5.56mm AR-15 pistol into a 9mm pistol simply by removing your standard AR-15 upper and replacing it with this 9mm complete upper assembly.

CMMG delivers its lightest and most compact firearms within the Banshee line of AR pistols.  This upper receiver features a forged 7075-T6-AL M4 upper receiver assembly with a bolt carrier group, and a hard coat anodized receiver and handguard. The Banshee is the right combination for you when concealment and portability matter the most.

The Radial Delayed Blowback (RDB) system was created from the ground up by CMMG to eliminate problems with traditional blowback systems found in pistol caliber AR-15’s. The biggest advantage of the RDB system is a gun that weighs less while simultaneously having less felt recoil. With a traditional blowback system, the only thing keeping the chamber closed is the weight of the bolt and action spring tension. As a result, the more powerful the cartridge is, the more weight is needed to keep the bolt closed long enough to safely operate. With the RDB system the bolt must be forced to rotate and unlock itself before it will cycle. This slows things down enough for chamber pressures to drop to safe levels ensuring reliable, and safe, operation without the need for heavy bolts or stiff action springs.


  • Forged 7075-T6 AL M4 Upper Complete with BCG
  • Hard Coat Anodized Receiver and Handguard
  • CMMG RML4 M-Lok Handguard
  • 8″ MT 4140CM SBN 9mm Barrel
  • Threaded Barrel (1/2×28 tpi) with thread protector
  • CMMG Oversized Ambidextrous Charging Handle
  • 15.3″ Overall Length

Additional Information Content

Modern Warriors

We started Modern Warriors for the sole purpose of providing a less expensive way to enjoy our love of buying and shooting some really cool stuff. What started as a hobby has turned into a business where we have developed the experience and ability to help you enjoy our same hobby and save you money in the process.

We specialize in tactical weapons, including suppressors, short barrel rifles and full auto weapons. We have routine experience in shooting the weapons we carry, so if you want our opinion on how a weapon operates, we will gladly provide it. We also have expertise working with licensed professionals in setting up gun trusts, which is an ideal way of purchasing, owning and operating any weapon restricted by the National Firearm Act. Don’t let the word “trust” scare you. It is very easy to set one up if you have the right help.

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