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No question about it, CMMG is making some of the best “conversion caliber” AR-15 upper receivers and magazines on the market. In the video above, I hit the range with the Radial Delayed Blowback 9mm and the direct blowback .22 LR CMMG Banshee 300 uppers.

Short version: they rock. Full, written review with photos and details of the inner workings coming soon.

[On some mobile browsers the Rumble video embed may not work. Click HERE to watch the video if you see an error bar above.]

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  1. What buffer weight & spring did you run with the 9mm upper?

    With a standard blowback 9mm AR, one usually needs a pretty heavy buffer weight & spring to go along with the usually heavy bolt. The bolt on mine weighs 15.5 oz & the buffer weight is 7.5 oz. The gun is annoyingly heavy but runs like a top with any kind of ammo and eats (formerly cheap) steel-cased 9mm ammo like kids breaking into a candy store. The Bushnell TRS-25 on top has spent years laughing at the term ‘recoil’.

    Looking forward to the in-depth review!

    • Standard rifle buffer (the stock is A2 length inside). CMMG suggests using a standard carbine buffer weight and spring for their radial delayed blowback uppers. That action delay is a pretty big deal and it eliminates the need for a super heavy buffer weight or additional weights added into the carrier or a non-standard recoil spring.

      • The 9mm mags. They are made by mean arms I believe. I’ve seen reviews that show using the endomag designed for “regular” AR-9s (non CMMG radial delayed blowback) if you put even the smallest amount of pressure on the bottom of the mag while firing they fail to feed. Do these mags do the same or is there a difference with their CMMG designed mags? Ever try shooting prone using the mag to support the rifle’s weight?

        • CMMG’s mags are different and designed fairly specifically for their own uppers. There’s no ejector and they’re designed to work with the standard stroke length of the CMMG action and the standard location of the feed ramp and such, all of which are generally different in straight blowback k9mm conversion uppers that the Endo ones are made for. At least this is my understanding. I’ll have to specifically test pressing up on the bottom of the mag for you before I write the full review, but I don’t see this changing anything. It’s standard Magpul PMAG geometry up top and the mags do not over-insert or anything. A 9mm case is exactly the same diameter as a .223 case and these mags hold 9mm rounds right where they need to be.

        • @Jermey thanks for the response. I would opt for the full CMMG upper if it doesn’t experience the same issues as the endomag when pressed on the bottom. If you have a chance to test please let us all know!

  2. My 9mm upper from PSA cost 330 and unless you’ve got a machine gun the delayed blowback to reduce recoil is kind of silly and not worth it.

    • That’s not true. If you ever shoot suppressed it’s more than worth it. The delay makes it far quieter for the shooter — really substantial difference — and less gassy. It also won’t break triggers like a lot of straight blowback 9mms do (the high bolt speed causes the hammer to slam down really hard, which brakes disconnectors and such) and it doesn’t require the half pound or so of additional reciprocating mass that a straight blowback does. It’s smoother and nicer shooting, too.

      • Can’t own a suppressor where I live, but I could own a “fule filter” 😀

        Haven’t had the disconnector issue. I mean, that’d be an issue if it broke them 100 rds in, but those parts are pretty cheap and easy to replace if/when they break.

    • My buddy built his AR9 SBR and only used top dollar parts.
      I have a CMMG Resolute AR (std 16” carbine) that uses the the same delayed blowback.
      Shooting them side by side suppressed you can tell a big difference. AND you can tell a difference in the recoil also, not like it’s that big of deal. The CMMG is quieter and softer shooting. And it doesn’t gunk up as fast using the can.
      And mine uses Glock mags for the win !!

  3. That’s frikn wicked. I probably wont buy it but still that is one cool shooter.
    Ammo, whew, that is a thing nowadays. You need to do a review on single shots, lol.

  4. Would like to also add that one of the best firearm accessories I have ever purchased was the CMMG 22lr conversion kit. As an instructor I immediately saw the potential in ammo savings. And man is THAT making a huge difference now. That kit just flat runs.
    It only shoots 22lr about 1.5” lower than 5.56 (using a red dot) at 25 yds. I don’t ever adjust the red dot, I just adjust my POA. Use the kit on my Aero carbine and my PSA pistol and it cannot be beat. Even using 22lr rated at 1250fps it still runs great. It is my go to practice add on for three gun, steel match, and running my walls course. Truly a great thing.

  5. I’ve fired one of their 5.5” 9mm radial delayed pistols and I liked it enough to order the parts to assemble an 8” barreled 9mm with their Glock mag lower. Hopefully I’ll have the parts by June 😐

    The radial delayed 9mm was much smoother than my AR9 just because the reciprocating weight is so much less. The recoil is still noticeably sharper than a MP5, but it is a neat system. The Endo-Mag is also a nice addition, because I will be able to use their 9mm upper on any of my other standard AR15 lowers. I just wish the mags were more reasonably priced.

  6. I ordered the CMMG Banshee 200 (same as the 300 just no Ceracoat) in .45 ACP back in August. It should be in their production run this month according to their Customer Service Dept. Glock mags.

    Can’t wait.

  7. Did you have to do anything special for the .22? I have the CMMG upper (older keymod model) with the antibounce/trip kit, and I still get bolt bounce in FA. I switched to a HiperFire FA trigger to get it to run reliably.

    • Nope, no tinkering needed. Has the little carrier weight thing and the auto sear trip thing of course, but it just ran right out of the box. I can’t tell if there’s any bolt bounce or not, but I can tell that it runs reliably. 95% of stoppages have been dud rounds and 5% magazine feeding issues usually related as far as I can tell to waxed rounds causing some binding when the magazine is loaded between 21 and 25 rounds capacity.

  8. The Banshee looks amazing, but quality control sucks from my perspective. I purchased a Banshee MK17 9mm and from the first magazine, the trigger reset is garbage. In my first outing I fired 100 rounds….probably 40 times the trigger failed to reset. Not sure I got more than 2 or 3 rounds in a row to fire. The gunsmith at the range took it apart and fiddled around with the safety and the trigger, then lubricated everything. But no real improvement. I contacted CMMG and they basically said I can send the gun back for repair (would take several months due to back log) or they will send me parts and I can try to fix it myself. I am reasonably handy, but not a gun smith. This sucks for a $1600 gun….all these reviews are positive….but they sell me a lemon and will do nothing about it. Don’t waste your money.


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