May 15, 2020 | AR-57

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Picture of a CMMG Banshee 300 MK57 5.7X28 AR Pistol


The CMMG Banshee line of AR pistols come in a wide variety of barrel lengths, calibers, and accessories, so you can find the right one for the job. The Banshee Mk57 is chambered in something slightly different than most pistol caliber carbines. Like the name suggests, it shoots the hot rod 5.7x28mm cartridge developed for the FN P90 and FiveseveN pistol.

Available at Brownells, Palmetto State Armory, and Primary Arms

CMMG Banshee 300 MK57 Five Seven AR Pistol

​Shaped like a rifle cartridge with a bottleneck yet short like a pistol round, the 5.7×28 boasts high velocity out of the 5” barrel and very little recoil making this a blast to shoot. The barrel is made from 4140 steel and salt bath Nitride finished for extreme durability. This is a radial delayed blowback rifle, so there is no need for a gas block or gas tube making for an extremely simple and reliable system. The 4” RML handguard features M-LOK slots for attaching accessories and features a top Picatinny rail that sits flush with the flat top upper receiver. The CMMG Mk57 Banshee 300 AR-15 pistol is a compact package that shoots a unique and cutting-edge cartridge.


  • Chambered in 5.7x28mm ammunition
  • 5” barrel with 1:9 twist rate and medium tapered profile
  • Machined from 4140 steel with salt bath Nitride finish
  • Threaded 1/2×28 with thread protector
  • Simple and reliable delayed blowback system
  • CMMG RML 4” M-LOK handguard
  • Forged 7075-T6 upper with Billet 7075-T6 lower
  • Graphite Black Cerakote finish
  • Magpul MOE pistol grip
  • Standard Mil-Spec controls and trigger
  • Pistol buffer tube with CMMG RipBrace
  • Includes one 20 round Promag 5.7x28mm magazine
  • Integral magazine release and flared magazine well

The upper is forged 7075-T6 while the lower is machined from a billet of 7075-T6 aluminum, allowing CMMG to create a proprietary lower with a custom aesthetic and compatibility with the Promag 5.7×28 magazines. The lower receiver features an integrated magazine release with a large, textured button and a flared mag-well for quick mag changes. This custom lower receiver also features an integral trigger guard and comes with a CMMG single-stage Mil-Spec trigger. Outfitted with a Magpul MOE pistol grip and the RipBrace, this pistol is extremely ergonomic and comfortable to shoot. Compatible with aftermarket AR-15 parts like the charging handle, safety selector, dust cover, and takedown pins, you can add a little flair to your CMMG Mk57 pistol. Additionally, it features a Graphite Black Cerakote finish.

A leading manufacturer of AR-15 rifles, kits, and accessories, CMMG Inc. was established in 2002. Constantly pushing the edge, CMMG strives to develop and improve bringing you a product lineup that is second to none.