I have been reading that, at least in the past, the 9mm RDB system that CMMG uses tends to eat ejector springs pretty regularly.  Was wondering if anyone knows if they've corrected that issue at this point?

I know they've started replacing 9mm ejector springs with the beefier 10mm version but I haven't seen if this has completely resolved the issue.  Probably need some higher round counts with these new springs to see how they hold up long term.

@amphibian is the resident expert here as he's done extensive testing with the RDB system.

tag

I installed the new spring in my 8 inch 9mm Guard yesterday.  Shot 200 rounds today, seemed to throw the brass further than with the old spring. Also, no malfunctions with Gen 2 Endomags. The old springs would start to fail after around 1000 rounds, so it's too soon to tell if this issue is fixed by the new spring.

I'm also at about 200, but have just a barrel and bolt on a home build... used the Bravo Company extra duty extractor spring, and retained the factory CMMG ejector spring (which has about 1200 on it, and has tension similar to a 5.56 bolt with a SOCOM bolt enhancement upgrade ejector spring)...ran well for the first match after the install...the extra duty extractor spring was recommended by a couple of posts on the Brian Enos Forum which is mostly oriented to the competition shooters like me... my center elastomer plug in the factory extractor spring had hardened... I removed it an am just using the HD spring by itself...will try to keep track of the shots

First of all, you may want to update the title of your thread....the CMMG is RADIALLY delayed NOT Roller delayed like an HK...

I have (2) 9mm 8" CMMG RDB setups and (1) .40SW 8" RDB setup.

I'm running all of them in full auto and like a cyclic rate in the 6 to 700's.   I can do that in 9mm with the Tubb 300BLK spring, A5 tube and RB5007.  However, when running that slow, I think the spring loaded ejector isn't as reliable...even with the new MK10 spring, I'm having ejection failures.  
I think it needs a faster cyclic rate to kick the brass out.....
So for 9mm, I use my custom fixed ejector setup that runs 100%.

I have been testing the new MK10  ejector spring but primarily in my .40SW RDB setup.  I only have about 300 rounds through it so far.....the original spring almost made it to 1K rounds.....so if the new spring makes it past that, it is an improvement.

Title corrected

I'll be interested to see what your results are.  Out of curiosity, what is your custom fixed ejector setup?

Discussed several times here but I have all this documented on my site so I don't have to dig up the details when asked: http://c3junkie.com/?page_id=538#section3

It’s secret sauce then.

Makes me wonder if endomags with the ejector could work if the ejector was simply removed from the CMMG bolt.

What I don’t understand is why the system kills ejector springs when 5.56 guns don’t.

Discussed that several times as well.  I think it has to do with excessive headspacing

Would this lower work? Could eliminate the bolt face ejector entirely.  Do these suppress noticably quieter than a blow back AR style 9mm? I've just got a 9mm can, but want quieter.

https://aimsurplus.com/foxtrot-mike-premium-complete-billet-9mm-pistol-receiver-with-sba3-brace/

That lower won't work because the ejector would be in the path of the bolt.

Right.  Also remember that the bolt has to rotate.  In my fixed ejector setup the ejector is mounted to the upper.  I had to cut slots in my carrier and bolt to make it work.  As posted before, I'm not at liberty to show pictures of it though.

I was wondering if the bolt carrier was slotted for a fixed ejector as I couldn't find a picture of the bottom of one. That was the reason for my OP. I think I've seen Banshee lowers with the fixed ejector. What am I missing?

https://www.google.com/search?q=cmmg+banshee+lower&client=ms-android-verizon&prmd=sivn&source=lnms&tbm=isch&sa=X&ved=2ahUKEwisx9KUy5rnAhUIT98KHax9B-UQ_AUoAnoECA4QAg&cshid=1579812285303&biw=393&bih=658#imgrc=CYGwInrVoapj3M

That pic is of their original straight blowback 9mm lower (Mk9).  I believe "Banshee" is CMMG's naming convention for all their short barreled guns.  So a Banshee can be a DI 300blk, RDB 45acp, or in this case a straight blowback 9mm.

Understood, finally. Thanks. Would have been nice though the build I had in my head.

Keep in mind, Olympic used (and still uses) an ejector pinned in the upper on their pistol caliber guns.  So there may be an alternative to an ejector in the bolt face - amphibian certainly seems to have found one, even if he can't show us.

FWIW, the 1921 Thompson has the ejector mounted in the upper.

Saturday I'm going to test my theory of CMMG DRB ejection problems.  My problem is that usually within a hundred rounds I have a failure of a spent casing not making it out of the ejection port. I'm using a CMMG lower. Here my logic, as the bolt clears the locking lugs the spent casing is allowed to rotate further away from center line of the bolt, much further than a 223 case because it is so much shorter. This leads to failure of the extractor to keep control of the case and then the ejector shoves it straight forward and you have your jam Stronger extractor spring and denser center plug for the extractor spring decreased the failures. Which I think adds to my theory extractor failure to retain the spent case long enough to allow the ejector to pivot the case out the port. So my plan is to reduce the ejector spring and polish and bevel the ejector plunger. My next action if that fails is to modify the extractor to allow it to move further in toward the centerline to be able better retain the tilting spent case. Sure wish I had really high speed camera, see what is actually happening and why the ejector springs fail so quickly, no theory on that problem. What are the causes of premature spring failure, heat and harmonics ??

What I think is the real solution is to set the case deeper into the bolt recess which will give extractor better control as the spent case moves off center line pushed by the ejector. Does 45acp have this problem? Will CMMG FIX THE PROBLEM. Might be too expensive if a new bolt and barrel are needed.

I'm using a cheap Casio Exilim digital camera...you can find them on Ebay.  Just do a Google search on the specs to make sure you get one that will do up to 1000FPS.  It can also do 480, 240 and 120 FPS and slower.  I think for troubleshooting ejection issues, 480FPS is good.  If you want to watch buffer movement you really need faster than 1000FPS.

I've been going back and forth with CMMG regarding my first 8" 9mm barrel.  I took some high speed footage to show them that my first barrel extracts with the extractor REMOVED FROM THE BOLT with no suppressor mounted.  I don't have that video publicly listed.

They finally agreed to send me a replacement barrel but I haven't received it yet....I guess they are all at Shot Show.

As posted in other threads, if you take a dummy round and chamber it, then push on the round with a rod, I feel the bolt lugs move a bit before the lugs of the bolt engage the lugs of the extension.  This happens on ALL of my CMMG barrels.

I had a custom SS 8" 9mm barrel made so that this headspacing slop is removed, I noticed that it would not extract a round with the EXTRACTOR REMOVED FROM THE BOLT with no suppressor mounted.

My second 8" CMMG 9mm barrel and my 8" CMMG .40SW barrel behave like my custom SS 8" barrel.  However, if you add a suppressor, my custom 9mm barrel, second 8" CMMG 9mm and 8" CMMG .40SW will all extract with the extractor removed.

I think that proves that my original 8" 9mm CMMG barrel has excessive headspacing causing too much shock.  So far I have broken several extractor pins, ejector retaining pins, a couple firing pins and also recently a cam pin broke too with that original barrel.

I've worn out several extractor springs, bolt springs and of course ejector springs with that barrel.

Breaking the cam pin is what really alarmed me and prompted me to do this additional testing.

I think some people have barrels that the headspacing isn't as excessive and that is how they are going beyond 4K rounds with the original ejector spring.

What is killing the ejector spring is that the spring is being compressed to 'solid height'.  As mentioned I've had several ejector retaining pins break from the shock of the ejector beating it up....if it is beating up that roll pin then the ejector pin is experiencing a lot of shock....and so is the ejector spring.

In conclusion,
I'm saying that if you remove the extractor and with no suppressor it doesn't extract doesn't mean it isn't going to wear the ejector spring as I've worn ejector springs on my 2nd 9mm barrel and .40SW barrel as well....
I'm saying that if it does extract with the extractor removed and no suppressor then it is extremely excessive.

I haven't heard about it occurring in .45.

As I posted above, my ejector spring died in my .40SW around 900 rounds.

I have the new MK10 ejector spring in my .40SW now and have only around 300 rounds through it so far.

Don't know that extraction w/ the extractor removed is all that unusual in delayed blowback systems.  High Points & STENs, both straight blowback, ie, the extraction delay provided only by mass, run fine w/o extractors.  Extraction in any blowback system is initiated by the case backing out of the chamber.

I would agree...but again, only my original 8" 9mm CMMG barrel does this behavior withOUT a suppressor.

That picture is of an MK9 lower.  They are blowback Colt, not RDB Glock.

Got it. I thought Banshee was a specific style. Not so. I'm hesitant to go down this path as I really like my blowback gun. But I've recently found that it suppresses really poorly. I would persue RDB only if it's significantly quieter. Is it? Don't really care about the smoother part.

CMMG replaced my bolt and carrier but problem still happens. The headspace and the angle on bolt lugs control the unlocking. The bolt moves a little to give the bolt some momentum so that when the bolt lugs strike the barrel locking lugs it will start rotating to unlock, the cam pin then shoves the carrier rearward. So cam slot is important also. Recoil impulse from my first bolt was different from my second. First had a mild impulse, second more severe.

Since the ejector and spring look the same as the 223 and stroke limited by the retainer roll pin I can't see that spring is going to solid, which will destroy springs quickly, I have not broken any roll pins yet, my first bolt did badly beat it up.

Post a video of the unlocking, how much bouncing is happening as bolt changes its rearward velocity.

Are you saying that the sloppy headspacing is by design?   I had wondered that too.  That is why I had a custom SS barrel made that has zero head spacing slop to test that theory.



As mentioned above, this barrel will not extract a round with no extractor installed just like my 2nd 8" 9mm CMMG barrel and 8" 40SW CMMG barrel.
However, adding a suppressor, it runs like my 2nd CMMG 9mm barrel....works fine.

Interestingly, I felt that the recoil is actually softer with this custom barrel that has no headspacing slop.

I don't know if you've looked at my webpage: http://c3junkie.com/?page_id=538
I've done a lot of testing with the CMMG in full auto.  I've gone through great lengths trying to get the CMMG to rival the MP5 in terms of smoothness and an even slower cyclic rate than the MP5.
Pictured below are modified 5.45x39 bolts to further delay the unlocking than a factory 9mm CMMG bolt.


I've finally accomplished rivaling the MP5 in smoothness and surpassing it with a more desirable cyclic rate by using a modified 5.45 bolt and going to a fixed ejector.  
I had the same reliability problems you are describing if I didn't go to the fixed ejector and having the level of smoothness desired.If you read this thread: https://www.ar15.com/forums/armory/Full-Auto-CMMG-Guard-Tuning/23-494385/&page=3
We are discussing theories as to why the ejector spring dies.  I think 'jbntex' does a better job of explaining it than I do.

Regardless, I have been running thousands of rounds in full auto with my fixed ejector setups with ZERO failures to eject....however it has been eating parts with that original barrel.  It was only recently that I put that setup on the high speed camera and noticed that it extracts without an extractor and no suppressor while my other barrels need a suppressor to do that.

I wish I had caught that earlier and notified CMMG as I don't think it would be eating parts with the 2nd CMMG barrel or my custom one.

I'm currently in the process of getting rid of a bunch of .40SW ammo and burning it up in full auto in my .40SW CMMG RDB setup.  I haven't converted it the fixed ejector setup yet.  I wore the original ejector spring out at about 900 rounds.  I'm now running the new MK10 spring and it has been good but I'm only at about 300 rounds.  I'm going to keep running it and see how long it lasts.  If it craps out too, then I'm probably going to completely turn my back on the spring loaded ejector and convert that bolt to use my fixed ejector also.

While my 9mm setup with the fixed ejector has achieved what I want, I'm always open to improvements/alternatives.  I didn't really want to resort to using custom parts but I felt I had no choice to obtain my goals at the time.

I'm looking forward to the Mean Arms roller delayed setup and want to do a head to head with that.  That setup also has the ejector in the bolt face so who knows if it may have the same issues or not.
Being that it is an entirely new bolt design, they were not limited to the design constraints of an AR bolt so hopefully they have fully tested their ejection setup.

Thanks for all the links... I like the theory the bouncing ejector. What I'm going to look at is which side of the ejector roll pin is beat up, both or just one. Next is to test the ejector spring travel, how far below flush, before the spring goes solid.

So I had mine out for steel plate match, and there two other RDB users who have the same problem, however they use non CMMG lowers. and we are all feeling screwed, not reliable enough for a match, or personal Defense. Mine failed on last round of the match !@#$

Those with fixed ejectors need to look at the 1911  Ed Brown article years ago  in handgunner article, what angles to put on them and what height, and the function of the Extractor in ejection.

So I've two more tests before asking for my money back

1. The Taccom magnetic delay recoil system, so unlike the hyd buffer, having the delay at the end of the stroke, we will put more something on while bolt is closed. Maybe the magnetics will act like added bolt carrier mass that disappears, or will act like non-linear spring? Tried it on blow back and the change was unique, a sharp but very short week impulse.

2. Will be to see if increasing the travel inward on the extractor by saw 0.20" helps.

Also using the ManntisX Recoil meter to see what can be learned.

I'm still mad at CMMG this was their job.

No doubt there is a wealth of information here, the kind of info you get from extended real live fire from actual owners. Read the reviews online,read info on this site, scrounged everywhere and was pretty well set on the RBD system, but guess I will wait a while to see more reviews from extended shooting and to see if CMMG get the bugs worked out.

I also have a page on my site dedicated to the ejection issues here: http://c3junkie.com/?page_id=954

However, I still think the root cause is excessive headspacing.  I think that is why this issue doesn't happen in 556.  A properly headspaced 556 barrel doesn't have this slop.

I think you are looking at the symptom vs root cause of the problem.

As I've posted before, chamber a dummy round then push on it with a rod and you will feel it move with no resistance then the lugs of the bolt will hit the lugs of the extension.

I think this is killing the spring and in my original barrel, killed extractor pins and now broke a cam pin.I'm fortunate that my buddy did all the leg work on the fixed ejector already and mine has been wonderful.

I had considered the Taccom magnetic setup but I don't want to lose LRBHO.

There is a long thread in the general section where we have been testing various buffers and using an accelerometer.  I was also using a Mantis X.  I have been corresponding with them and they told me to only use it for muzzle rise and that the accelerometer in the Mantis X won't give accurate readings for recoil (in case you were hoping for that like I was).  I had issues where the Mantis X wasn't counting accurate shot counts and need to test again.

I also had a rifle length buffer tube milled out to watch buffer and spring movement for all these tests at 1000 frames per second.


This video shows how smooth my preferred configuration is


And now the factory CMMG recommended configuration:


I was shooting from a lead sled to minimize the human factor.  You can barely see any rearward movement on my setup.....it is extremely smooth.

I certainly concur that CMMG should have ironed out the bugs more....but in the end I have what I wanted albeit with custom modifications/parts.

I'm happy with it but I do wish I didn't have to do that.

I'm hoping the new MEAN Arms roller delayed setup will finally be the holy grail for me....
Ejector is in the bolt as well but as discussed in the following link, it is not spring loaded.
http://www.uzitalk.com/forums/showthread.php?91585-CMMG-banshe-on-RR-questions/page4

If the MEAN Arms roller delayed setup doesn't work out, I still have my 'FrankenGuard' and plan on running my custom barrel + modified 5.45 bolt with no slop and fixed ejector.  I believe with no slop, it won't break parts anymore....and from my testing, still very smooth.

FAILURE NOTHING WORKED

So back to stock with new ejector extractor and springs, no weight in carrier and 223 flat wire springs.

Tuesday I'll take it to another match

Yeah. I only made it to a little over 600 rounds with the original ejector spring. A big let down. Kind of disappointed with CMMG. They did send me the MK10 ejector spring and so far I have only 350 rounds through it.

I don't mind tinkering but if the MK10 spring fails I'll look into making my own fixed ejector. That will require cutting a slot in the bolt and bolt carrier then modding the upper receiver. Hopefully it won't come to that.

Today's response from CMMG

we have changed the ejector and extractor springs in those. we are currently waiting a shipment of the extractor springs. as soon as we get those in, i can send you replacements.

joe dodson. technical support representative
cmmg, inc. | po box 68 | boonville, mo 65233
tel: 660.248.2293 ext. 322 | fax: 660.248.2290
e-mail | online

amphibian, and CKing... you probably already mentioned it, but I missed it... what brand of magazine are you using with your RDS?....amphibian you are using a Colt format I believe, and CK a Glock... is that correct?

and if Glock, have either of you tried a 40 round ETS or 27 Magpul ?

mine seems to be running again, but only two matches ~ 250 and another 100 testing... thank you

It's definitely not heat.

My theory is that, possibly, the bolt has a very short bit of rearward travel before the bolt lugs engage the barrel extension.  Possibly causing the ejector itself to compress the spring via the inertia of the ejector.  This could possibly be a fairly energetic event that compresses the spring farther than it is designed to handle.

I haven't had any failures yet with my initial spring that came in the bolt.   I do have the upgraded spring to swap in if/when the original one fails.  Round count is somewhere around 500 rounds right now.

I initially tested with the CMMG 'Guard' Glock lower as my 'control' for functioning, then used the Colt 9mm mags and now just run the Endomags....(talking 9mm here).  Also have the CMMG RDB in .40SW and use the CMMG Guard Glock lower for that caliber and ETS 30 round mags.

thank you

This thread appears relevant to my interests...

I started getting stovepipes after about 150 rounds of semi- and full-auto fire. CMMG sent me a replacement ejector spring and so far that has worked well after 60 rounds of semi-auto fire.

So much info on the cmmg ejector spring but somehow I still feel all alone.

My build, CMMG rdb with 8 inch barrel and standard buffer spring.
Initial issue, gas key screw loosen while shooting breaks off on the charging handle and locks up the upper. CMMg makes good on it and sends me a new BCG.
While waiting for the new BCG I decide to change out the buffer tube to the A5, 9mm hydraulic buffer and Tubbs recoil spring
2nd bcg 200 rnds in and again the screws loosen, this time I tighten them before any damage, 400 rnds later ejector spring failure.
Again cmmg makes good and send me out a new bcg.
3rd bcg 800 rnds in and ejector failure.
Cmmg makes good again and send me 4 new MK10 springs

Currently Im noticing
While Using my reloads 9mm 115 gr 4.9 wsf the ejection seems to be worse under the hydraulic buffer system vs the standard 556 buffer system.
While using factory ammo the ejection works well.

Has anyone notice that using reloads with the hydraulic buffer and tubbs spring slows the cycle rate too slow and causes premature ejector spring failure.

Not going back through all the pages, does the ejector spring problem happen only on 9mm?

I haven't seen anyone post about it happening in 45ACP or 10mm.  I have had mine fail on my .40SW at about 900 rnds.  I've replaced the ejector spring with the new MK10 spring and at about 700 rounds on it so far.

FYI... my 16" 9mm made the third match yesterday (my hand loads are 135 polymer coated at about 1050fps), about 500 rds since removing the extractor spring insert plug and replacing with only a Bravo Company extractor spring and no O ring... the original ejector spring is still functioning... probably 1700 rounds... regards

NO!!!

Amphibian's website is down. I went to double check the MEAN mag conversion recommendations and got a 404.

Thank you for your selfless dedication to the mission Amphibian. Please send me your PP address so I can contribute to the cause.

Sorry guys...I've had c3junkie.com for what over 15 year?  I don't know...
One of my buddies has been hosting it for me for over a decade and he's out of business.  I took money out of my pocket to pay for hosting for another 3 years....I am going to have to rebuild everything but honestly haven't been that motivated to keep it up.

You guys can go to here to see the last archive.  Looks like the last snapshot was taken in August of 2019: http://web.archive.org/web/20190818042513/http://c3junkie.com/

@Amphibian - I would be willing to donate to the c3junkie.com website cause as well. Your contributions to our community are outstanding and having all of your knowledge bundled coherently in one place like that was fantastic!

Esox

Edit: never mind, I’m a moron. It’s just like an AR15 ejector.