Fixed! CMMG 9mm AR15 Rotary Delayed Blowback Upper On WWSD 2020 Lower Made Reliable!

[@BlokeontheRange]

So as a bit of an update on this, I have not had a single jam on it since replacing the ejector spring, and even managed to run it in a PCC match (which I won 👼) and it ran like an absolute champ. I've put a Walker Defense Research NERO 9 compensator on it and discussed it in a video here: kzbin.info/www/bejne/nqHUgHifbt5geqM

[@musician445]

Glad to hear that its running so well despite not using the CMMG recommended MK4 upper which has a enlarged ejection port hole. I don't want to use their upper so this is good news to me. I'm curious though, would this run in a 9mm dedicated lower, like one that takes glock mags? I know some of them have feed ramps in the lower which i know obviously won't work, but i've seen others that don't have feed ramps on the lower. The feed angle might still be off but it makes me wonder.

[@TheOz91]

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.

[@dbmail545]

Bolt velocity is very important. Too fast and the gun "stovepipes". Too slow and it will misfeed. I have several guns that have needed tuning to run a particular load and accessory combination.

[@Rileysworld727]

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.

[@BlokeontheRange]

I found the whole process quite interesting, if frustrating! It's annoying that CMMG aren't open about this - it only seems to be a proportion of uppers that are affected, and I feel that they should be communicating more openly a) on buffer weights, and b) saying "if you have ejection issues, do this".

[@Rileysworld727]

@@BlokeontheRange Im curious if the JP silent captured spring system caused the ejector spring to wear faster than it would have otherwise or if it was just a bad spring

[@BlokeontheRange]

Given the way the spring's not even straight any more, I suspect a bad one. But it seems to be that slight hesitation as the lugs engage that causes the issue, rather than anything to do with the JP SCSS or anything else.

[@dbmail545]

I have never had nor heard of an AR-9 that did not need some amount of troubleshooting and tuning. Delayed blowback actions are notoriously finicky.

[@markpileggi643]

@@BlokeontheRange I have a Banshee pistol with a 4 inch barrel and do not have this problem (yet). I purchased it complete (upper and lower. I will have to go out and pound a few hundred rounds through it to see if it has any problems. I will let you know what happens.

[@ArsonFire00]

You've cured my insomnia. 👍

[@carlwimmer403]

Thanks so much, Bloke. I have a 4 y. o. CMMG 16” Guard (MKGs) that I use for 2-gun , USPSA and IDPA PCC competitions. From the beginning, it has had ejection/extraction problems. One trip back to CMMG where they rebuilt the BCG (fixed for a short while), ejector spring replaced (fixed for short while), lots of advice online to not much avail. All this with about 2400 rounds through it. Then I stumbled across your KZbin channel. Watched it several times and absorbed the math and physics. Finally it made a lot of sense what the real problem is. Stripped the gun, complete clean and lube, replaced ejector and put in D. Tubes HD ejector and extractor springs. Best advice of all, put in J-P Enterprises silent captured buffer system with light (std.) weights and heavy (15-100) buffer spring. Result: perfect ejection of almost 100 rounds of five different loads of 9mm, three factory and two of my reloads, ⅔ without suppressor and ⅓ with. Light loads ejected at about 1:30, factory loads at 3:00, and +p loads at 4:30. Will be putting it through its paces in competition starting next week. Again, many thanks.

[@BlokeontheRange]

Glad this video was of help!!! :D

[@dd61999]

@carlwimmer403 any updates on how this is working for you?

[@williamlloyd3769]

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

[@0Asterite0]

I'm still convinced roller delay is one of the best light recoiling systems for pcc. Recently got a JP5 and it's been amazing so far. Reliable, accurate, and fast. Though very expensive and hard to get right now

[@BlokeontheRange]

I'd like to try one of the JP's to be honest :)

[@0Asterite0]

@@BlokeontheRange Unfortunately it's a whole proprietary system and they only have glock mag lowers at the moment. It uses an mp5-style rocking ejector in the lower so you wouldn't be able to use a normal lower with the mean arms mags. I think you mentioned those were easier to get and use where you're at than high cap handgun mags.

[@oskar8413]

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.

[@dbmail545]

An easier solution would be to use a traditional solid, frame mounted ejector like most other 9mm PCC's. Using an ejector meant for rifle-length cartridge cases is a problem with pistol-length cases necessitated by this hybrid operating system. I have three 9mm PCC's that are all straight blowback, all have frame mounted solid ejectors and none have this sort of problem.

[@0Asterite0]

someone on arfcom had a gunsmith do just that to his upper, along with modifying the carrier and bolt to accommodate the new fixed ejector. It sounded like a pain to do tbh. Glad bloke fixed his issues tho

[@diamant1337]

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.

[@davidcolter]

I agree, I think the center of gravity of a pistol case is too far back for this style of ejector to work effectively. The ejector push produces very little sideways displacement of the CG and so the case does not exit the receiver in time.

[@BlokeontheRange]

To be honest, I'm amazed that CMMG setup runs at all (I think I said as much in the vid).

[@spraynpray]

I think you're right and I never thought of it before. All my PCCs have a pivoting or fixed ejector and run great.

[@commander31able60]

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.

[@milsurpmarine8628]

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.

[@spraynpray]

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.

[@steveh1792]

I've been using a 16" CMMG upper on a KP-15 lower for competition for about two years. Function has been flawless (but I still got the David Tubbs spring set to install this weekend). The only issues so far have been pure pilot error.

[@georgewhite8528]

The clapping Python Ladies, magnificent.

[@dbmail545]

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.

[@Fugettaboutit]

What you are describing was exactly what I was describing a few years back in a forum discussion comparing a 5.56 case ejection vs. the RDB's 9mm one. The analogy I used was comparing, of all things, the cores of a roll of toilet paper to that of a roll of paper towels, by trying to flick them away using just your fingers. The added rotational/centripetal momentum of the longer paper towel core will swing that out with more authority and it will fly farther, whereas in comparison the shorter toilet paper roll will not have or fly as much. Pretty much same with the RDB and 5.56 v. 9mm. This is the major weakness of this design amongst all that it does so well. This ejection plunger thing is better suited to rifle-length casings whereas a fixed/'blade' ejector would have been better just like on essentially anything else for pistol casings. Also yes the nature of the blowback vs. rearward piston action puts more compression on the ejector spring which contributes even more. The rifle cases are in rotation and being flung as soon as they clear the chamber, whereas the pistol cases achieve exit more on just being knocked out by the rearward BCG stopping....essentially by luck without the aid of a fixed ejector specifically knocking it out and away, and why they can sometimes just stay in the action and jam things up. Also why they just trundle down on manual ejection/cycling. I saw someone who actually modified their RDB to incorporate a fixed ejector blade, and it solved it completely but required some milling of a channel for that blade. Anyway, mine are working well with the extra power springs, but I also keep an eye on round count, expecting to change springs every 1200-1500 round. Par the course I guess with this system.

[@BlokeontheRange]

Yup. I just keep an expensive Tubb spring in my tool kit that I take to the range so if I have a problem I can just change it out.

[@bedroomfarmer8960]

How many rounds has the tubb spring lasted?

[@astrodudepsu]

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.

[@BlokeontheRange]

Have you tried replacing the extractor spring too? I'd be interested to hear if that helps.

[@astrodudepsu]

I did yes. That one is easy enough. No dice I'm afraid. Also running the standard JPSS weight with the same spring you are. Its all F=ma, so I know there is a solution. Maybe next winter I'll tinker more. I'll buy a couple of that exact brand of ejector spring. I had been using BCM enhanced ones. Good luck Bloke.

[@dd61999]

@@astrodudepsu any updates?

[@astrodudepsu]

@dd61999 well CMMG themselves have admitted the problem. You'll notice their new Dissent line integrates a stand alone ejector. They know it's not working as intended. As for me, I've migrated to the JP-5 platform. It is currently the gold standard.

[@jl-jf9ny]

Just Ordered a set from Brownells UK for my straight pull having issues with it ejecting (ejector is on bolt face not on lower receiver like some 9mm AR's ), always having issues hopefully this set will be strong enough.

[@Scott-qq9jd]

Hmm, sounds like I need to put a bunch more mags downrange with mine, just to be sure. It's never had issues before, but why not test it more?

[@MrS22222]

Very well done!

[@1982rrose]

Great analysis Bloke.

[@peterconnan5631]

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.

[@BlokeontheRange]

I'm not even sure a toothpick would fit down that spring, and if it did, it would certainly get beaten to crap. They're really very tiny in diameter.

[@spraynpray]

I'd have to see one to confirm, but such a low pressure round could likely use a bigger ejector and spring. Unsupported chambers are common enough in 9mm recoil pistols and the clearance slots for fixed ejectors on SMGs are large.

[@peterconnan5631]

@@BlokeontheRange i don't have an AR so I can't measure it, but considering that the only force on it will be the inertia of the ejector and the fact that it would be pretty well constrained by the spring itself, I am pretty confident that it would last if made from proper heat-treated steel.

[@Kaboomf]

@@spraynpray Yes, just give the ejector a larger diameter head that stops it flush.

[@cedhome7945]

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?

[@BlokeontheRange]

No, only citizens can be in the army

[@simonjones6128]

Good job Mike

[@loquat44-40]

The video is old but still of interest. What I have noticed is that at least visually there appears to be some variation to 9x19 luger cases. So your remarks about ejection angles might also vary with the particular dimensions of different 9 mm ammo lots. You use guns for gun games, I use them for practice and if need be for self defense. Reliability must be as close 100% as is possible. The nice thing about AR systems is that parts of all sorts for them are available and so if it does not work with one part, well then switch it out for another. For now if I want a 9x19 carbine, I buy something that from the ground up was constructed to fire that round. The only 9mm carbine I have now is a high point lol. Bit it works with the low capacity factory mag.

[@kingerikthegreatest.ofall.7860]

Well done.

[@viperscot1]

Love this type of informative entertaining video Even though I don't do real steel shooting keep up with the excellent informative content Got nerd overload 😁😁😁😁😁 Bestest from Scotland

[@zacharytremblay9481]

My ejector roll pin had a broken half moon piece out of it

[@erikdijkshoorn3231]

Had to look up Brian Boitano...

[@Simon_Nonymous]

I'm so happy :-)

[@ATH_Berkshire]

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.

[@spraynpray]

In their defense, if the springs last 200 rounds before dying, most customers will never see a failure.

[@BlokeontheRange]

Reading forums where other people have had this problem, you read things like "I've had about 250 rounds total through it now", and those are the guys that are actually shooting them. Mine has probably had over 1k through it and I've only had it since mid-December, with not not many opportunities to shoot it!

[@anthonyleesmann9863]

Just question here, and you may have stated in another video. Did you purchase complete upper or build? If build, what stripped upper did you use? Thanks

[@BlokeontheRange]

Complete upper

[@rickoshea8138]

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?

[@rickoshea8138]

@@noele6588 That is the idea, but somehow the bolt starts moving before the BCG. Too much lash in between locking lug surfaces...

[@mediocrist]

Have you had any issues with the ejecting cases chewing up the rear portion of the ejection port? I'm reading it's a bit of an issue on some examples and would like to know how it can be dealt with prior to maybe purchasing one.

[@BlokeontheRange]

Nope, but after about 1000 rounds it's eaten another ejector spring so I need to swap it out again...

[@NomadShadow1]

Cool

[@umarmars47]

To me the ejector spring/mechanism is a design flaw. So much for a versatile platform..

[@dd61999]

Any updates on this? How often do you have to replace the springs?

[@BlokeontheRange]

About every 1000-1500 rounds.

[@Tom_2025_]

Please move your reddot forward, it's not a scope..

[@scipio10000]

Problem solution boring? Are you kidding me?

[@ianvincent4911]

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.

[@BlokeontheRange]

I like the CMMG mags, and they were a big part of why I chose the system. If the feed ramp dies, not a big deal - mags are consumable items.

[@ianvincent4911]

@@BlokeontheRange Fair enough. Perhaps its lack of experience with these mags, on my part.

[@Scott-qq9jd]

I haven't seen issues with tbe feed ramps, though the followers do get a little gouged up on mine. Hasn't caused function issues yet.

[@sparkyatlarge]

You want to be careful running a light buffer on a 9mm Blowback system. It will run faster, but the possibility of an out of battery experience is higher because it's blowback. Now, having said that, it seems to me that the CMMG system is more akin to a regular AR-15 locking set-up, so as long as the bolt is locking into place, you are GTG. Just something that occurred to me.

[@BlokeontheRange]

Part of the advantage of the delay system is that you can run a standard buffer weight.

[@DebakulumToughguts]

👍 für den Algorithmus

[@bigguy8749]

I’m selling my upper

[@fomocore]

It's only temporary. Nobody Bet Your Life on these models. No AR style 9 mm is reliable

[@BlokeontheRange]

It's a range toy ¯\_(ツ)_/¯ And I've not had a problem since, despite having chucked large quantities of ammo through it :)

[@dd61999]

GMR-15

[@bigguy8749]

Don’t buy this upper. It’s very heavy.

[@smokeyjoe1122]

CMMG is trash......