Well I don't have the .45 CMMG RDB setup myself but one of my local shooting buddies does have it and he uses my recommended buffer // tube // spring combo for the 45 as well and works 100%.  Also in full auto with a RDIAS.  However, he is using a Bazooka Brothers lower with modified grease gun mags.  I presume it would work with the CMMG .45 lower but he doesn't have that lower.

I have a spare PA10 tube from converting to a rifle stock. I'll pick up the flat wire from tubbs and the blitzkrieg buffer and give it a shot. I'm using a angstadt matched receiver set with the CMMG parts.

@amphibian
Got an A5 question for ya. Didnt wanna disrespect OP by asking it here.

I wanted to test out the 9ARC mags before committing to building an SBR from an 8" CMMG upper.  I have a full CMMG 9mm rifle so I mated a BCM lower to the 16" rifle upper.  Haven't shot it yet, but the mags need a good tap to load on a closed bolt and retracting the bolt puts a pretty good scratch on the top-most case.  I suspect I'll see scratches on most of the ejected cases.  Don't know, that being the case, if I will want to reload these cases.  Anyone else notice this with the 9ARC setup?

Has there been any updates on ejector spring life? I had probably over 1000 rounds of various stuff in my Guard and then it started throwing brass inside the gun. Just got a new ejector spring from CMMG about a month ago, and has resolved the problem. Just not sure if I should stock more ejector springs, or if this new one should be good to go for an extended period..

Active thread on that here: https://www.ar15.com/forums/AR-15/CMMG-radial-delayed-system-ejector-spring-question/15-747732/
CMMG is saying it has resolved the issue but I don't see anyone that has had the issue report back with more than 1K rounds through the new MK10 spring.

Bear in mind there are some people that say they have 3 to 4K on the original spring (even in full auto usage) with no malfunctions.....I'm not one of those.

Mine have all died around the 1K mark.

As discussed in the other thread, I believe that those that are getting over 3 or 4K on the original spring have tighter headspacing than those people that have had theirs die.

I truly hope that the MK10 spring resolves the issue but I'm personally highly doubtful.

As posted in the other thread, I've given up on even the MK10 spring for 9mm as I'm still getting malfunctions with it but that is with my modified 5.45 bolt that further delays the action to be smoother than the MP5 and with a more desireable cyclic rate.  My fixed ejector setup is 100% with my modified 5.45 bolts and runs awesome.

I still use the MK10 ejector spring for my full auto .40SW CMMG setup.  I'm at about 300 rounds and if it dies at around 1K, I'm going to totally turn my back on the spring loaded ejector.

I sent CMMG as copy of my invoices and requested the new Mk10 ejector spring. We will see.

Probably the wrong place to post this but this setup has been discussed a lot here so here goes.  In process of building a 9mm Banshee (just the barrel / bolt remaining).  Finished my SBR lower assy and took it out to shoot today with a factory 5.56 LMT 10.5 upper and it was short-stroking every round on 3 different types of ammo.  I used a POF 308 7 position extension, 9mm Kynshot buffer and 5.56 Tubb flatwire.  This upper has been flawless so I just wanted to see if anyone has had problems with the @amphibian setup and 5.56.  I know it's too short but I installed a standard carbine buffer for a few rounds and it was fine.

I figured the POF extension would work since the measurements were the same as the A5.  Could be wrong.  Any thoughts?

What are the 3 ammo types you've tried?

Works fine in my 10.3" MK18

Federal xm193, Radway L2A2 (admittedly a little light but cycles all my rifles), AE 223 55gr

Amphibian,
I’ve scanned the thread but may have missed this, so bear with me... Do you think that there is any value in short stroking the system? I know that you’re using the RB5007 with the A5 receiver extension to maintain last round bolt hold, but I wonder if the Guard bolt carrier can be notched like Taccom’s ESSB and the combo used in a regular RE?

Sorry if this has been answered but do geissele triggers work in the banshee?

Yes. I run an SD-C in mine, no issues.

Not sure what to tell you.  I've run all of that ammo with my buffer/tube and spring setup with no issues and even in full auto from my 10.3" MK18.  
I have some old Radway Green 62 grain...don't know if that is the same as the L2A2 but whatever it is works fine for me.

Are your gas rings in good condition?

Yes, a nice feature of the Guard is that it has the same carrier geometry at the bottom as a 556 carrier and is softer shooter so no need for specialty straight blowback triggers.
Geissele SSF in mine.

Bear in mind that as mentioned on my site, I have a specific set of goals I'm after.  http://c3junkie.com/?page_id=538
One of them is to get a slow full auto cyclic rate.  Short stroking it would be counter productive to my goals....

In fact, I've been playing around with the opposite....

I have a modified carrier key for my CMMG RDB that matches the new Surefire suppressor optimized carrier to give another 3/8" or so of travel....still testing it though.

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

I received an email with shipping information from CMMG yesterday (Feb 7).  They are sending:

10BA455; Spring, Ejector, Mk10
45BA45E; Spring, Extractor, MkG
55BA4C8; Buffer, Extractor, AR15

ETA - parts arrived today (Feb 10).

love mine ... and I like the weight system they have for the bolt carrier ... this one came with their "rip stock" which i absolutely hated and replaced after my first range trip.

ETA - I should add that I swapped out the spring/buffer when i swapped out the factory rip-stock because of longer carbine buffer tube. I run it with a geissle braided spring and a H1 buffer with the middle weight in the bolt carrier. Runs like a top

Checking back in again!

Just as a quick re-intro for any who weren't following. I have a 16" 9mm build using a standard carbine spring and carbine buffer. It was having a light strike every 100rnds roughly. Between 150rnds and 600rnds when I didn't clean it at all.

Last update was at 800 rounds and the rifle was cleaned at that point.

Since then I have put another 275 rounds through the gun in two range sessions still only using the Fiocchi 115gr 9AP ammo. First trip was only 100 rounds as I was adding some riser blocks to the red dot to make it a 1.93 height. Had to re-sight it in and played around with it to see how the new height was. Nothing bad to report as far as light strikes and ejection was still strong.

Next trip was yesterday for a six stage Steel Challenge match. Fired roughly 175ish rounds. Had one light primer strike on my second to last stage. Cleaned the rifle when I got home. Each time I clean this rifle after 200-300 rounds I'm finding quite a bit of residue on all the internal parts. One thing to especially note is I find a lot of residue on the front, skinnier, portion of the firing pin just before the tip of the firing pin. Wonder if this might be my problem as the light strikes don't occur right after clean but as I'm approaching 250ish rounds after cleaning. They still aren't super frequent though. May be just a dirtier ammo and the combination of one in one hundred having a slightly harder primer. Either way I had confirmation from the ROs that the ejection was still strong as they complained about the casings coming straight bas and hitting them.

All in all about 1075 rounds down the barrel of my 16" using the recommended carbine buffer and buffer spring and it still has super strong ejection.

I think I posted before I haven't had any light primer strike issues....well except when the firing pin broke...other than that, none...
Have you tried using a 556 chamber brush to clean your extension out?  Wondering if you have a bunch of crud not allowing the bolt to get deep enough into the extension sometimes.

I do have a chamber brush and did that at the 800rnd cleaning and again this time at 1075rnds. def got some junk out of there but I don't think it was the main issue. May try another firing pin and see if that helps. So far though cleaning seems to help it the most.

I got my new ejector spring from CMMG a little while ago.  I haven't replaced it yet.  I never changed an ejector spring before and didn't realize it required special tools.

I hate to buy a tool that I'll probably only use once.  How are the rest of the poors changing ejector springs?  Is there an inexpensive tool that I'm missing?

Yes, there are inexpensive tools to change the springs.  Check Brownells.

749-003-708WS
Sinclair AR-15 Bolt Vise
Mfr Part: 14950

$24.99

But I made my own.  You need a vice, a small block of wood and a 9mm empty brass.  Drill a hole in the block of wood to accept the tail of the CMMG bolt.  Put the brass in the bolt and compress with the vice.  Tap out the roll pin with a punch.  I replaced the brass with a shortened bolt for a little more stability later.  Wear eye protection.  YMMV

Thanks!  Not sure how I missed that one.  When I looked at Brownells before, I saw a couple that were over twice the price of that one.

When searching around, I saw references to an AR15.com branded block, but can not find one of those anywhere.

Here you go Link to Brownells

I got it and like it.  A little fussy to get the bolt in, but it works and the price is good.

Thanks!

I don't know why I couldn't find it when I searched, but the link worked.

And that's why I love the MCC rifles (LE901, CM762)

Here is the latest news from CMMG on FTE, I'm using CMMG lower, barrel and bolt.

"We updated your mag well and mag catch as we have made some design updates to those areas since your lower was shipped out. The mag catch modification allows the mag to sit a little bit higher to allow for a .40 S&W upper group to utilize the same lower as the 9mm.  This also requires a new mag catch as well.  The mag well  modification allows a little more clearance for Glock magazines. We have seen that Glock changed their mag specs after we released the 9mm lower. The newer spec magazines have clearance issues in our lowers causing feeding issues. This modification alleviates that issue. We also changed the design of our bolt carrier assembly. So we updated that as well"

So this will be my third bolt, a test video will emailed Monday, and the gun following my approval

So far CMMG has been very good taking the gun back and making repairs, I hope this time it is solved.

Thanks for posting this!

Interesting to hear all of the changes.  I would love to see some pictures of the changes.  I wonder how they could 'update' you mag well.  I presume mill on the catch area to allow the catch to be placed higher?...but sounds like it is just to run .40SW w/ newer spec .40SW mags..but I thought you weren't running .40SW?  So why bother?  
BTW, I am using my CMMG lower for full auto .40SW currently as I have a lot of .40SW ammo I'm burning up.  Mine has been fine feed wise.  I primarily run the 30 round ETS mags with no issues.  It is just the ejector spring failure issues just like 9mm I've been having.  Although I'm at about 700 rounds on the MK10 spring in .40SW at the moment.

I'm mostly curious what BCG changes they made.  Not really clear if they replaced your BCG or made changes to your current one.  Please share with us what you notice on that when you get it back.

Thanks again!

I sent in a very early 9mm, so some of the comments left me baffled also. Supposedly Monday I get video maybe I'll know more then. My guess is a new mag catch and bolt.

Nevermind.  I'm dumb.

@CKing
Thanks for the follow up.  Hoping your squared away finally.

I've got new MK10 ejector springs to try in mine.  Just haven't been able to yet.

Video came in today, they took a 33 Glock mag and did a dump, the ejection was very consistent. That was part of my criteria, shoot federal or Winchester 9mm 115gr from Glock factory mags and shoot a whole match without a failure. Now we will see if it can do it for more than 1000 rounds.

Almost ordered a GibbzArms left handed 9mm Bolt, lower, Side charger upper.

Good to hear it seems to be working now. Would love to see some comparison photos of the new BCG when you get it back if possible.

Here is what the repair label listed as work and parts

Update mag well and mag catch window to current spec

Replaced BCG and updated mag catch

Comment flat wire recoil spring won't run

standard carbine spring and buffer installed runs fine

I'm still waiting to hear from people that shoot a lot more than I do whether or not the new spring from CMMG fixes the ejection problems.

@amphibian

I read your posts about using a custom setup with a fixed ejector.  I know you can't talk much about it, but a question just hit me this morning.

I use my SBR lower with multiple uppers (5.56, 300 Blackout, and 9mm).  Is the fixed ejector setup something that works in such a way that other uppers can still be used with the lower?  Apologies if you already addressed this and I missed it.

Yep.  The fixed ejector in my setup is located in the upper and requires slotting the carrier and bolt....in fact I just slotted my .40SW RDB bolt and another 5.45x39 bolt yesterday...I'm going to try to do CPR on my website and have some pictures uploaded soon....unfortunately none showing the fixed ejector details....my buddy still won't let me do that.

Glad to hear it's in the upper.

After I made my post, it occurred to me that it could be on the mag like the non-CMMG Endomags.

I understand about pics or too much detail, and appreciate your response.

I don't think you could do it with the ejector on the Endomags...I personally wouldn't want it that way either.

Hey guys, I've been slowly putting content back up on my website.  I just added a page detailing the ejector springs and issues.  I also added two videos that I have not made public before.
Here is a link to the new page: http://www.c3junkie.com/?page_id=221
I'll post the videos here for everyone's convenience.
This short video shows the excessive headspace seen in one of my CMMG BBL/BCG combos.  All of my factory CMMG setups do this.  (2) 9mm and (1) .40SW.
There is a dummy round in the chamber in the video.  The rod is pushing on the nose of the bullet.  You try this in a 556 upper and there will be zero movement on a properly headspaced barrel.


And here is a video that I had sent CMMG regarding my original barrel that I think has extremely excessive headspacing and was breaking parts.
If your CMMG extracts with the extractor removed and NO suppressor mounted then I think the barrel needs to be replaced.


As mentioned on my site, I've asked CMMG if the headspacing slop is by design but wasn't given an answer.  What I do know is that the custom SS barrel that I had made and headspaced to a .40SW bolt (since I was planning on using it for a dedicated suppressed barrel) while feels smooth, it is not reliable with any buffer/spring combo I tried with the spring loaded ejector as I think it is robbing too much energy away and there is not enough BCG velocity to reliably kick the brass out.  I am dedicating that barrel to my fixed ejector setup which works great and has none of these issues.

I also even tried the new MK10 spring with my custom barrel that has no slop and it isn't reliable either....so I think some slop is required for the spring loaded ejector....no slop then you need to fabricate a fixed ejector....

First off do we know if the barrel extension on the cmmg is any different than the standard  AR?

LETS assume it is not

The effective head space is needed to make the system work. When locked the recoil spring keeps the carrier up against the bolt and bolt up against the breach face. Upon firing The bolt transfer it energy to the carrier and the bolt they move rearward together until the bolt strikes barrel extension lugs and stops while the carrier continues rearward. The cam pin cause the bolt to rotate and unlock after the carrier has moved fixed distance rearward. The time it takes the carrier to move rearward and unlock the bolt is the delay.

Now the question does the bolt bounce forward after striking the barrel extension lugs, does the angle cut in the bolt lugs effect that? Is there pressure still in the barrel, holding the bolt against the lugs? The cam pin shows some fairly severe polishing as due the bolt lugs. So now we've got the bolt going forward or stopped as carrier is still moving rearward. The separation of the bolt and carrier forces the can pin to rotate the bolt. The momentum of the carrier pulls the bolt rearward. The bolt lugs show wear which means force while unlocking my guess still pressure in barrel.

My first BCG had very mild recoil, but failed, second version had much increased felt recoil, but failed.

Did they  both fail due to dead ejector springs, don't know I never checked  the first bolt, but I did on the second bolt and new springs didn't help.

So now I'll be on the THIRD BCG, we will see how it feels and does it make it past 1000 rounds?

I've looked at their patent and they do show a modified extension but it appears they didn't incorporate that into production....at least the examples I have seen.   I have two firearms patents myself and there are some things we didn't do in production either.

I don't know if you've read my posts about my website but I'm in the process of rebuilding it.  I know I posted the picture below but I'll post it here again:

That is a factory CMMG barrel and extension.  I have (2) 9mm CMMG BBL/BCG combo's and (1) .40SW...they all look like that.
I have some discrepancies on your description but I think if we both talked this over verbally instead of typing all this we would agree on how the thing works.

Rather than waste time going over that, what I'm trying to illustrate in my second video is that my first 9mm CMMG barrel has way too excessive headspacing which is evidenced by being able to extract fired rounds with no extractor installed and no suppressor mounted while my 2nd 9mm CMMG barrel and 40SW require a suppressor mounted to do that.

Also, I would argue that the headspacing slop is only required if using the spring loaded ejector in this design.  This has been proven by me getting that custom SS barrel made that has ZERO slop.
Below are pictures of my custom SS barrel and I'm using a standard unmodified LWRC 5.56 NiBor extension I bought surplus off CDNN like a decade ago.



Pictured below is my 9mm CMMG RDB setup on a full auto lower.  Custom SS barrel with standard 556 extension w/ zero slop using a .40SW CMMG RDB that has been slotted for my fixed ejector setup.
I had accidentally put my CMMG carrier in my ultrasonic cleaner with CLR and it stripped the finish off completely and it has now been NP3+ coated.  This configuration works awesome and gives me the full auto cyclic rate I want, totally reliable and I believe I'm not going to be breaking parts anymore since the slop is totally gone....but I'll be keeping an eye on it if the bolt or extension lugs start wearing and developing slop.

I have run many thousands of rounds with the fixed ejector slotted carrier pictured below....mainly with modified 5.45x39 bolts with angles cut to delay the unlocking further than the factory 9mm bolts.  Most of the rounds I put down range were with the original 9mm barrel which kept breaking extractor pins but even with broken extractor pins it had never malfunctioned and now I know why, the headspacing was so bad, the extractor wasn't really doing anything as shown in my videos, it was extracting on its own the entire time.  Regardless, the fixed ejector setup has been extremely reliable for me.  I would have kept running it and replacing extractor pins until I finally broke a cam pin.  

I think the RDB has got some inherent problem that makes it eat ejector springs, maybe means roller lock will be better. I hope this third BCG solves the problem.

Yes, I've got high hopes for the MEAN Arms Roller delayed and posted about it here: https://www.ar15.com/forums/AR-15/The-ultimate-9mm-NON-straight-blow-back-AR-M16--MEAN-Arms-roller-delayed-system-related-/15-748519/

The MEAN Arms has the ejector in the bolt as well but if you've read the posts, it looks like there are no spring so nothing to wear out.

Back on topic of the CMMG, I'm pretty convinced it is headspacing that is the source of the problem.   Catch 22 is that if you eliminate the slop you need a fixed ejector like what I have for it to be reliable.  Bottom line is they should have released it with a fixed a ejector from day one and none of this would be an issue.

I was looking through some pictures I have stored on my computer and found this old picture I saved of the fixed ejector of the LaFrance 45K which is straight blowback to give you guys some hints...Thanks goes out to whoever took this picture.  I can't remember where I got it.

I had Macon Armory build me a direct-impingement 45 ACP that I pinned to a Quarter Circle 10 large frame lower.  The gas system is stupid short.

Runs like a top, next to no recoil, cool factor, etc.

That said, it seems the CMMG guard is a bit of a game changer.  I'm getting ready to take the plunge with a 9mm

Picture of my DI45...

Here's what I got back from CMMG

A new BCG, carrier now has the round logo and patent no on it
The firing pin spring is longer and heavier
bolt looks the same, has a heavy spring in the ejector
can't tell if cam slot or bolt lugs have changed

New mag catch with logo
mags have to be fully seated before it will catch, and it holds the mags much  tighter

We will see if it makes it past 1000 rounds, but that will take awhile since all matches cancelled.

I'll shoot it soon to see if a subjective change in recoil, my first BCG Shot very soft, second BCG felt like direct blow back.

I'm curious of the firing pin spring, 1st version had none, 2nd had a light one, third BCG has a heavy one.
'
I think it is trying to control bolt bounce