CMMG Banshee: The Unique Radial Delayed Blowback System

In 2015, the CMMG company decided to develop a pistol-caliber AR carbine firing .45 ACP. Such things were becoming common in 9mm, but .45 was a more open market opportunity. They spent substantial time trying to perfect a simple blowback system, only to find that the recoil impulse was causing occasional feed failures that just couldn’t be rectified. They next tried using the regular AR “direct impingement” operating mechanism, but that wouldn’t provide enough energy to run the system reliably – and was very direct to boot. Just when the project looked hopeless, they took inspiration form the WWII Reising submachine gun – a delayed blowback .45ACP system.

Thinking about delayed blowback options, they hit upon the idea of using the AR cam pin as an accelerator lever. By cutting the back of the AR bolt lugs at 45 degrees, they created a system where the bolt would try to rotate and unlock under direct pressure from firing. This rotating acted through the cam pin to accelerate the mass of the bolt carrier rearward before the bolt head could start to extract the cartridge case. They named the system radial delayed blowback, and proceeded to spend 2016 perfecting the system, ultimately releasing it in April 2017 to the market. Following that, they expanded their product line from .45 ACP to include 9×19, 5.7×28, .40 S&W, and 10mm Automatic.

There are very few new ideas in firearms operating system these days, and the radial delayed blowback is a clever and elegant one, using an existing set of parts in a novel way.


  1. I’ve not watched the video yet, but the description of the operating system sounds very much like agnelli’s villar Perosa.

  2. Great stuff!
    “Innovation” is as brilliant as it is useless.
    Of course, if you do not agree to replace the bolt and cam pin every 500 shots.
    Really forgotten.

    I could be wrong, but I don’t think so.

  3. I was getting excited about having a PCC in .45 with a converted AR mag. Then I went to the website. Only the 9mm comes with a converted AR mag.

    • You cannot stuff 2 stacks of .45 cases into an AR magazine. Duh.

      Remember how original GWACS had the magwell widened so that a .45 ACP magazine would fit, and that WWSD 2020 lower disposes with that mod. It was discussed at FW.

    • Oddly enough, feeding an AR conversion from Glock magazines works better in .45 than in 9mm. The cartridge is longer, so the feed is more controlled for the same vertical displacement. It’s still a little challenging, because there’s not much space to back the magazine up enough even with a bespoke lower. But the burning pressure to resolve the problem is not as great as in 9mm.

  4. Whilst it a totally inadequate weapon in the combat situation, the Riesling was a very effective policing weapon. The USMC in Australia in 1943> supplied gratis to the Prison Services of Victoria, South Australia and West Australia, a quite substantial number of the SMG (with a modified sear to allow only semi-automatic fire). These lasted until 1950/51 when due to a sheer lack of spare parts they had to be disposed of, and replaced in each State by the Commonwealth Government supplying M1 Carbines abandoned in a Ordnance Depot along with much more in 1947, and used until the 1970’s until all replaced the M1 with Ruger Mini 14’s. Much of the abandoned US Government property was paid for by the Australian Government and used to equip hostels for the huge wave of Displaced Persons from Europe. And the standard ‘short’ gaiter of the US Marines were used in the Australian services until the 1980’s, blackend with Raven’s Oil.

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