Fixed! CMMG 9mm AR15 Rotary Delayed Blowback upper on WWSD 2020 lower made reliable!

I'm so happy 🙂

Well done.

I was trying a straight pull 9mm today (it has a standard bolt head btw (just works on no gas), from the previous video comments). I was having similar issues, which would have been a similar bolts speeds as you were manually demonstrating. Being the demo model, I wonder if the springs had the same issue. I will check back with them. BTW what is your opinion of the CMMG magazine over glock type AR mags? I found the CMMG magazine rather fiddly to load and I am unsure how resilient the polymer feed ramp is going to be.

Bloke, I had the same problems. Came to the same solutions. Ran the gun in USPSA for exactly a year before the springs gave out again. However, this time when I swapped the ejector spring, I'm still getting the failures. Didn't have the time or ammo budget to test every other component, so I went back to using an MP5. Just a warning for your future, if you use the upper heavily in competition.

I reached out to Les at Polaris about an MP5-AR9 lower for my CMMG build and he said CMMG QC is "non-existent" and I shouldn't bother. guess I'll wait for a while.

Loved how you diagnosed and fixed the problem. Not being an engineer, I could not have figured that out.
By the way, I have no idea what the sticker on the butt stock means.
Thanks for another interesting video.

Good job Mike

Super happy for you and glad you posted this! My buddy sold his. I bought a delayed stribog, tested it successfully, ended up selling it to him. In the meantime, I got myself some roller delay toys.

I nerd out for PCCs and would own a CMMG if I'd had a good experience just to have one.

I wonder what it would take to add a receiver mounted ejector? Or an in-bolt version of the standard one, that gets a kick from when the carrier over-rides the hammer.

The above may sound stupid, but the AR was not designed for such a short case…

If the problem is the free travel of the bolt before it is delayed, what about decreasing the lash in the locking lugs that allows the free travel?

Good to see a troubleshooting video on that system. With three 9mm PCC's already, I can't really justify purchase of the CMMG but it is an interesting concept.

Cool

Great analysis Bloke.

Makes sense. I wonder if the spring's life can be extended by making a dowel pin that fits inside the spring, with a length such that the ejector can only be pushed down to a thou past flush with the bolt head? In theory that should prevent the spring from ever going coil-bound.

I think its interesting how ive seen so many guntubers say great things about the cmmg banshee including Ian. But they all have just assumed that you could just drop the upper on any lower and it would work. Thank you for telling us what cmmg should have told their customers in the first place.

Don’t know what everyone thinks but to me it looks like CMMG didn’t do sufficient testing and engineering analysis on this product before launching it to the shooting public. They shouldn’t be relying on customers to workout how to get the thing to run long term reliably.

Seems the proper solution to this problem would be a complete redesign to a static ejector to make the 9mm cases not want to torque out of the extractor before clearing the barrel extension. But of course, that would be a huge undertaking for a problem that can be fixed with a balanced system as we see here instead.

Very well done!

Had the same kind of issue with a Rem 788, which I tried to convert to 45 acp. I figured that pistol calibers really dont like spring plunger type of ejector. The rim is too heavy, and theres not enough leverage to pop the cartridge out of the rifle properly. And the case ends up turned 180 degress inside the ejaction port. Even if the port is flat with the chamber opening.
A fixed ejector is much better for pistol calibers. My experience relate to bolt actions, a faster operating semi automatic might be different.

Ended up giving up my hopes and dreams, of cheap and easy to find sub sonic caliber, and bought a Ruger american in 300 blackout. Even if it had been really cool to bring a rifle to a handgun range.

Had to look up Brian Boitano…

I find the deductive reasoning very interesting thanks for showing us the why and how .living in Switzerland are you expected to help defend the country or is that only for national citizens?

Problem solution boring? Are you kidding me?

The clapping Python Ladies, magnificent.

It's really interesting that this system relies so much on bolt velocity in order to properly eject an empty case! The reason that I love this channel is because how much geekery is in it, explaining things that I–who is yet to be an owner of any firearms yet had a decade's plus interest in them–with my engineering graduate mind would appreciate. Really makes you think that it's the little things that makes the difference between a gun that runs perfectly fine and a gun that jams every so often.

So close but yet so far to closeout this issue! Way to go on a thoughtful problem solution process.

Wowee