I posted my build and initial shooting trips here. My parts list is there in case anybody wonders what other components were used. I was just loving the thing until I took it out for it's 3rd trip with a big group of friends yesterday and it appeared to have the ejector spring issues others have reported. The thing is that I had less than 300 rounds through this before the issues started.

The trip yesterday was a disaster, with failures occurring more frequently the more we tried to shoot it. At the beginning of the day it shot a full mag with one issue. By the end of the day it was failing every 3rd shot. We only shot 100 rounds so it went downhill really fast. I noticed that even when it didn't completely fail to eject, some cases were barely ejected and fell just a couple feet from the shooter.  Most ammo was Blazer Brass on all 3 trips. Picture of the issue here.

This has undermined my confidence in the thing so much that I don't know when, if ever, I would trust it for home defense. Not even sure where to go with this thing right now as guns I can't trust are useless IMHO. Just really bummed.

I sent an email to CMMG tech support and will update on the process and results.

Good luck with that.  4 emails and 2 weeks. I feel like I am getting the runaround.

DWCOYOTE... can you slowly work the action with an empty magazine inserted without any drag on the magazine or follower ?

Do you have access to a trigger pull gauge?
As documented on my site here: http://c3junkie.com/?page_id=954
I put the bolt in a vise then use a punch to push on the ejector and pull down with the trigger pull gauge.

I think at 5lbs or under is when you start having malfunctions.

New .45 CMMG RDB spring is about 8.5 lbs while the new MK10 10mm spring is about 10lbs new.  
Looking at your old post, you bought yours early this year and the MK10 was already out by then but who knows how long yours was laying on the shelf and if CMMG was proactive about supplying all 9mm RDB bolts w/ the MK10 spring.
I suspect you don't have the latest spring but again, if you measure the strength, you will know what you are dealing with.

As I've posted several times, I believe the issue is inconsistent headspacing of the bolt and extension which is why some people are claiming over 3-4 K of even full auto usage on the original spring....this is even before the MK10 spring.

I just don't believe ANY spring can handle the about of an excessively headspaced barrel....just too much shock.

A test to determine if you have excessive headspacing is to remove the ejector from the bolt and with no suppressor mounted, does it extract the round?

My original barrel does that and after several emails and high speed videos proving this, I finally got CMMG to replace that original barrel.  My 2nd 9mm CMMG RDB barrel adn .40SW don't do that unless I add a suppressor.

Lastly, you will want to check the strength of your extractor spring and make sure the extractor pin isn't broken.

My original barrel with the excessive headspacing was breaking extractor pins, extractors and finally broke a cam pin.

I had high hopes for the RBD system, so much so that when it was released, along with the glowing reviews, I was convinced that I had found an out of the box pistol system that would work and fill my needs. It seems as though that isn't the case with the problems documented on this site. Guess I will wait a little longer before purchase.

I won't be near the gun until at least tomorrow but I will check. I have not noticed any drag up to now or any wear on the mags or followers, but I will look closer with that in mind.

I will try as much of that as I can tomorrow or the next day. My trigger pull gauge got lost in a move so I don't have one currently but I may decide to invest in another. Thanks for the info!

Yes, I see no wear on the mags/followers and if I hold the bolt catch down it feels the same working the charging handle with or without the mag inserted

No trigger gauge but I tested the spring by feel and it feels way stronger than 5 lbs

The extractor pin is intact and the spring feels stronger than my 5.56 bolt which runs perfectly.

I will consider testing with the extractor removed tomorrow when I test CMMG's suggested fix, which I will note below.

Update: CMMG's suggested fix was to clean it. This initially made me very angry because I felt like it was a lazy answer. After all, 300 rounds should not be enough to cause a gun to fail, right? Also, after each trip I run a bore snake through, spritz the bcg with MP7 and wipe it off, and re-oil. I do a thorough cleaning after 500-600 rounds on most of my guns. So to me it should not have been that dirty and it shouldn't have mattered anyway.

However, I sat down to clean it so at least I could rule it out. It was extremely dirty. The amount of carbon that came off the barrel extension, carrier face, carrier bore, and the inside of the receiver was excessive. So after almost 2 hours of cleaning while watching Jojo Rabbit (awesome flick BTW)  it is as good as new. I will test tomorrow to see if that translates to function.

I am somewhat disappointed even if this does resolve the issue as I wanted this to be a gun I could toss in the trunk every time I went to the range with some cheap ammo and minimal maintenance like my buddy does with his AK-V.  If it is going to be hypersensitive and slow to clean after each range trip I will definitely lose some love for it. But I will update after I get back from the range tomorrow.

Thanks for the advice so far!

Anxiously awaiting your update. I was just about to order one. I've got a bunch of the recent 9mm PCCs and I don't treat any of them gently or clean them often, but they keep running.

No 300 doesn't sound like enough to create as much fouling as you described.

I don't clean mine that much...maybe every 1k or so...and many times it is just adding lube and I may scrape stuff off the carrier but just doing preventative maintenance not from any malfunctions.

DWCOYOTE...if you are willing to try something else... remove the polymer "helper" plug in the middle of the extractor spring, mine had hardened and would not let the extractor claw move...amphibian and I have two similar but different problems... my problems were both double feeds (live rounds) and failure to fully extract fired cartridge over live feeds... which on the face I've blamed on the extractor not snapping over a live round case during feed

I eliminated the extractor plug and replacing the spring with one from Bravo Co.... last two 120+ round matches and 100 or so reliability check rounds without problem ... I'm still using the factory ejector spring...

We got rained out yesterday but I was able to get out and test today. No joy.

Initially things looked good. I loaded 10 rounds into a mag and ran through all 10 without an issue (remember it was failing on every 3rd at the end of my last trip). Cases seemed to be ejecting with a lot more authority. I was beginning to think that it was going to work, but was going to be a princess that required everything perfect.

Then the second mag of 10 rounds produced a failure. The 3rd produced 2. The 4th and 5th had 3 stoppages a piece.

I will let you know what CMMG has to say.

I bought a used ultrasonic cleaner for my RDB.  1st time using mine yesterday, 20 mins running, wiped down bolt with oil, bore snaked the barrel and no failures.  I need to figure out a way to fit the barrel extension but I'm happy to clean that by hand for now.

I had to travel unexpectedly so I apologize for the lack of updates. After a few rounds of communication with CMMG they asked me to send the upper and mags in for inspection and were kind enough to provide a shipping label. I will let you know what happens.

Update:

CMMG got back to me today and said that they had to replace the bolt from my bcg. They sent video of shooting it and it was flinging the brass out harder than it ever did on the old bolt. It shipped out today so I am eager to try it out in a couple weeks. Fingers crossed that it is smooth sailing from here.

The upper arrived from CMMG yesterday and I immediately headed for the desert to try it out. Oddly it seems like there is less dot jump on the sight at the same time it throws the brass almost 3 times as far as it ever did with the original bolt. They didn't tell me what was wrong with the original bolt, just that they replaced it.

Anyway it ran perfectly so I hope that continues. I will report back if I have any issues or when I get to 1000 rounds on the new bolt with no issues.

I sure do love it when it runs!

One last note for this thread: I have to give CMMG service an A+, through it all they were awesome! Great communication and every indication that they wanted nothing more than to get it right.

I hadn't seen this post previously.  This is exactly where I am with my 8" CMMG upper.  My FTE issue literally moves with the bolt.  I can duplicate the problem by installing the bolt in my factory 16" CMMG upper.  CMMG has a new bolt on the way.  They had previously supplied replacement springs and a new extractor.  This really gives me hope that I'll be able to get my new upper running.

No surprise.  I just responded to you in the other thread regarding the bolt issues.

Noted as I'm in the same boat.  I have "new" MK10 spec springs from them and we shall see how that fares.  I guess if I start getting stove piping again I'll have to inquire about a replacement bolt?

What other thread? I want to read it. Still trying to decide to go this route or wait for one of the sometime in the future roller delayed systems.

I responded to him in this thread: https://www.ar15.com/forums/ar-15/9mm-CMMG-versus-300-BLK-SBR-recoil/15-750350/?r=8068392&page=1&anc=8068392#i8068392
May want to check out the last few posts I made here also: https://www.ar15.com/forums/ar-15/Thoughts-on-the-CMMG-Guard-/15-713060/&page=24

As mentioned in a few threads, it seems several people have posted about getting defective bolts from CMMG lately (with one that I personally got to test).  Who knows if they got a bad batch or what.  Bad news always spreads faster than good.  

It still seems yet to be determined if the new MK10 ejector spring has cured the ejection failures for good....me personally, I'm running the new MK10 ejector spring only in my .40SW RDB setup and am at 700 rounds while the original died at about 900 rounds.

Don't think I'll wait for Mean RDB to hit the market, so CMMG it is. I want to clarify one point for myself. I looked at the A5 tubes. There's no way to use this in a braced pistol configuration, right?

Sure you can, I use an SBA3 brace on an A5 length tube.  Look for the Leapers/UTG 308 tube; well made, A5 length, alot cheaper than Vltor/BCM.

Another update: Cleaned and oiled up the RDB build on Sat and went out yesterday for more testing. A few rounds in I had another FTE. The bolt crushed the case good. That is less than 100 rounds on the new bolt. You may be saying "ONE failure, so what?", well I then had my son shoot a few mags through it and I watched the ejection closely. 9 of 10 shots would throw the brass 10-15 feet but on 1 in 10 the brass would just fall out of the port and land at his feet. My feeling is that it was probably very close to failure on those as well.

I am somewhat reluctant to contact CMMG after just one failure but I don't know in these times of expensive ammo that I want to keep dumping ammo playing Guinea Pig either. I have no faith in this as a defensive firearm and I don't know that I ever will. If I just wanted a 9mm range toy I would have just put a PSA 9mm together or bought a Ruger Carbine. Yes, I am salty.

Edit to add: One other thing I noticed, the harder the brass is thrown the more rearward it is thrown. So the 15+ foot brass is thrown at 5:00 and a left handed shooter would get hit straight in the face.

Sorry if I missed it but what buffer / spring and ammo are you running?  Suppressed / unsuppressed?

To start out I wanted to stay very standard per CMMG's recommendation. Sprinco white spring and a KAK standard buffer. Not suppressed.  On the old bolt I ran a mix of Winchester white box, Remington, and Blazer Brass. On the new bolt all ammo has been Blazer Brass as its all I have left.

Also the PSA PA10 tube works great.

On a side note, I realized tonight that using a SBA4 brace with these longer tubes will put you over the 13.5" ATF "regulation"

Yep that one too!  That tube was actually my first choice but they've been sold out forever.  I thought I read somewhere they're no longer making the longer ones and just using standard AR tubes with shorty buffers in their 308 guns now.

You can see in the video I posted on my site here: http://www.c3junkie.com/?page_id=280
that 115Gr Blazer brass was jamming on the CMMG factory config when fired from my lead sled.  It wasn't jamming when I put it on my shoulder but I don't use this ammo much.  I mainly reload 147Gr subsonics.  I just got this stuff back when they had some promotion.  I just use it for cheap unsuppressed blasting ammo.

Sorry I don't have more definitive data to give you.  I don't blame you on not trusting it.  I've posted before that I've pretty much given up on the spring loaded ejector for 9mm since I believe that the more you slow down the delaying, the more prone you are to having ejection failures.  I'm still on the fence on it for 40SW as I'm at 700 rounds so far with the MK10 spring..  If it doesn't make it past several thousand rounds, I'm going to be doing surgery on that bolt also and setting it up for the fixed ejector and totally running away from the spring loaded ejector.

What is interesting is that there are people out there that are at beyond 3 or 4K even with the original ejector spring with no malfunctions....some even running my recommended spring/buffer/tube configuration in full auto and suppressed conditions.

Obviously, I'm not one of those lucky people....all (3) of my CMMG combo's have had their ejection springs fail around the 1K mark.  (2) 9mm and (1) 40SW.

Again, I believe the issue is a combination of the bolt lug angles and the amount of headspacing the barrel has.  The people that are getting high round counts with no malfunctions with the original spring must have a combo that is in that 'sweet spot'.  I would love to meet up with someone that has a setup like this and do some comparisons.....actually, I do know one person that responded to one of my youtube videos says he is at 4K running with no malfunctions that shoots at my monthly match but that has been shut down.  Hopefully when all this Covid stuff passes over I can take a look at his setup.