CMMG banshe on RR questions

[chili17]

Are you using an A5 setup? I’m pretty sure that’s what amphibian is using. I can send you a tube n buffer...

No A5 tube. I thought I had one, but I do not. The buffer tube I took off an AR10 was only 7"

 

[amphibian]

the 40S&W bolt/9mm barrel combo would not function for me, failures to eject. Tried and tubb 300blk spring and carbine buffer with no weight. This was with 115 and 147gr ammo. I will try it with a suppressor this weekend.

Yeah...as I posted before, mine stopped working even after replacing the ejector spring which is really strange. I did receive some replacement springs from CMMG made from their new material but haven't tried it yet.

FWIW I spoke to a couple of guys at the KCR match and they claimed to have between 3-4k on their uppers with no ejection issues using your buffer set up. That's about what I get on a MP5 before I need to replace the extractor spring.

You referring to me? I'm glad to hear some KCR SMG competitors are running the CMMG RDB and to hear them running my configuration is even more awesome. How did they do? They running Endomags or Glock mag setups? Interesting to hear they are not having ejection issues. I don't know anyone that has run 3-4K with no issues.

 

[chili17]

Yeah...as I posted before, mine stopped working even after replacing the ejector spring which is really strange. I did receive some replacement springs from CMMG made from their new material but haven't tried it yet.



You referring to me? I'm glad to hear some KCR SMG competitors are running the CMMG RDB and to hear them running my configuration is even more awesome. How did they do? They running Endomags or Glock mag setups? Interesting to hear they are not having ejection issues. I don't know anyone that has run 3-4K with no issues.

Yes sir

They both were running the Endomags. I honestly do not remember how they did as I was watching the ejection pattern and ROF.

 

[Jmacken37]

So...

Optimum setup for full auto 9mm unsuppressed is:
1) A5 length buffer tube
2) Kynshot RB5007 buffer
3) Tubbs 5.56 spring
4) 8" 9mm CMMG barrel and bolt combo (not 40S&W bolt)
5) endomags

Do I have that correct?

 

[amphibian]

So...

Optimum setup for full auto 9mm unsuppressed is:
1) A5 length buffer tube
2) Kynshot RB5007 buffer
3) Tubbs 5.56 spring
4) 8" 9mm CMMG barrel and bolt combo (not 40S&W bolt)
5) endomags

Do I have that correct?

Uh....I guess you didn't read everything I did here? http://c3junkie.com/?page_id=538

I broke it up into 4 sections to make it easier to digest.

For someone that doesn't want to tinker, I would say go with what you have listed. As mentioned on my site, components 1,2 and 3 work great for me for 5.56 and other calibers/configurations. If you want to get about 30RPM slower, then use the 300BLK Tubb flat spring but bear in mind it is kinda weak for 556. So staying with the 556 Tubb spring makes it a straight upper swap for many configurations.

If you want to delay the 'unlocking' more then read up on how I modified 5.45x39 bolts. (that is what I'm running now). (discussed in section III on my site).

 

[Jmacken37]

Ok, let's be honest...the ADD was kicking in.

I read in more detail and it looks like you've been messing with the carrier, the ejector, and the bolts. I don't think I'm up to grinding bolt lugs and machining bolt tails.

So, going with the Tubbs spring, A5 buffer tube and the Kynshot RB5007, AND removing the carrier weight (I didn't realize the RDB carrier had a weight in the end) you are getting between 622 and 686 RPM. I'm assuming that is with different brands of ammo? What sort of ROF are you getting when the carrier weight is left in?

Thanks for all the testing. I really like the AR manual of arms/ergonomics and am looking forward to setting up a subgun using this platform.

Have you messed around with CMMG's "action tuning set?"
https://www.cmmginc.com/product/action-tuning-kit-mkg/

 

[amphibian]

Yes, as posted on my website, unsuppressed was 622 RPM while suppressed was 686 BOTH with no carrier weight....and again, the cyclic rate will drop around 30 RPM slower going to the 300BLK Tubb but will reduce compatibility with other caliber uppers.

By default the 9mm CMMG RDB does NOT come with any weight. I think only the CMMG 10mm RDB comes with a weight by default.

Yes...if you read the link I referenced I discuss and show some pictures of some of cyclic rate results using the 3.5 oz (heaviest carrier weight) as well as a custom 5.1 tungsten carrier weight.

I also tried the lightest and the medium weight and never really liked any of them (discussed on the AR15.com threads). I don't like increasing the reciprocating mass.
Just like you don't throw mass at an MP5 to slow it down, you change the locking piece to slow it down mechanically. Modifying bolt geometry is the best way to do this.

CMMG posted this themselves but doubt they will ever do it.

I also posted the following on my website:
You may be thinking, ‘who cares since the RoF achieved with the first configuration suppressed was 686 RPM vs 663 RPM. However, what is hard to quantify is smoothness. As discussed earlier, it is no big deal to get down to even the 400′s but then it is too bouncy. Cyclic rate data is good but you really need to shoot it side by side to get an appreciation of the progress.

During my testing, I was constantly shooting side by side an MP5 trying to match it. I was only able to achieve this two ways, 1. with the spring loaded tungsten weight in the carrier to increase the delay and help mitigate the initial recoil impulse ...but it wouldn't work suppressed and 2. modifying the bolt angles.

However, I guess some would say I'm being too critical and doing just the buffer, tube and spring changes are sufficient and I think of all the people I know running the RDB only one other person is running a different bolt like I am. He actually bought a 40SW BBL/BCG combo just to get the 40SW bolt and his is still working fine with that 40SW bolt while mine no longer works after wearing out the original ejector spring.

Most people are happy with the buffer/tube/spring recommendation and leave it at that. What I like is that since it is basically an AR, there are so many parts out there to make it do whatever we want.

 

[chili17]

so far mgi buffer with tubb 300blk spring seems to be shooting the softest. This is with 147gr. With 115gr it is still choppy. Waiting on a A5 buffer tube at the moment.

Combos tried:

Endine buffer with tubb 300 and 5.56 recoil spring=bouncy

Standard carbine buffer and spring=fast

h3 buffer (would only work with tubb 300blk spring)=bouncy

MGi buffer with tubb 300blk and 5.56 spring. Failures to eject with 5.56 spring

****edit

This was with an extra power hammer spring. It was choppier with a standard hammer spring

After finding the mgi buffer with tubb 300blk sping and extra power hammer spring to be the smoothest combo (with what I had with me) I shot 180rds with 1 failure to feed. All shooting was done UNsupressed

 

[Jmacken37]

Going out tomorrow sorry for the delay! You want an A5 buffer too?

 

[chili17]

Going out tomorrow sorry for the delay! You want an A5 buffer too?

Thanks, Jake!

 

[Jmacken37]

If you want to get about 30RPM slower, then use the 300BLK Tubb flat spring but bear in mind it is kinda weak for 556. So staying with the 556 Tubb spring makes it a straight upper swap for many configurations.

Amphibian,

I couldn't find the 300BLK spring on Tubb's website. Is that a call and request item?

Never mind! I found it...

http://www.davidtubb.com/tubb-springs/ar15-buffer-spring-stainless?sort=p.price&order=DESC&limit=100

 

[charlie0369]

I had initially jumped onto the endomag insert the bandwagon with my colt pattern 9mm upper by NFA. After a dozen inserts I gave up and they gave me my money back and let me keep 4 inserts. My BCG just did not work with the inserts. So I had to wait for CMMG to release the 5" barrel/bcg combo kit so I could build a Guard setup. All i did was trim off the damaged ejector tab and viola it's a guard insert. Just finally got a chance to run it and I'm floored. The weight savings alone is worth it. The guard inserts are worth it, the versatility of being able to tune the ROF was worth it. I have a MVB Arc Ti stock and was able to use their standard buffer weights vs the proprietary 9mm buffer. I tossed all the traditional stuff onto an SBR and used the 9mm MVB buffer/stock with it. On the guard setup i have several standard buffers that i was tuning with different weights. This video has the h3 in it and the ROF is smooth and slow enough for me. Cmmg Guard and the endomag inserts are a game changer and i am stoked about this setup now. 5" barrel with a pdw stock that is super light weight. easily carried in bag or on a sling. Don't have a pact timer so no idea what ROF it is but i'm good with it. If you listen, it almost sounds like suppressed is slower than not. weird

I had read through Amphibious's entire page. Now he was using standard buffer tube/stocks. I like my pdw stocks, so I was determined to use my MVB. The only problem i have with it is that i have failure to feeds with speer 147subs due to them being truncated. I had little american eagle 147's and they worked well cause the flat nose was quite smaller vs speer. But to eliminate all the projectile variable problem, Armscor has 147gr round nose for pretty cheap in bulk case w/free ship from targetsportusa.

My next tesst is to take my lower out and hot swap at least 4 different uppers w/o touching a single thing on the lower. 22lr, 9mm, 5.56, 300blk and i'll have to borrow a 7.622x39 upper. But having the ability to take four uppers and one lower makes for a way easier packing of guns to shoot with.

Also having the 9mm pmags eliminate need for different carriers on my chest rig.

https://youtu.be/7JfO48pL4RY

 

[amphibian]

If you had straight blowback Endomags with the built in ejectors then you don't have the gen2 Endomags made specifically for the CMMG RDB.
I have this documented here: http://c3junkie.com/?page_id=969
I would hope that the gen2's would feed your truncated rounds as the gen2's have a conical feed ramp and 'wings' that go over the feed ramp.
MEAN Arms will swap them at no charge.

 

[charlie0369]

You don’t say? Well they let me return the damaged ones that i paid for but in the time of diagnosing they sent me over a dozen. Gave me my money back to. Can’t remember his name but he let me keep 4 of the 1st gen blowback and i just trimmed off the ejector. That would be sweet since i still have 5k of lawman still. Thanks the the info. I’ll he sending them in for the 2nd gens.

 

[localizer11]

Made my first trip to the range with RDB CMMG 9mm upper with very good results. I used Amphibian’s setup with the Tubbs flat wire spring, Kynshot 9mm buffer, 2ng gen Endomags, and my SP-1 RR. Shot over one hundred rounds with a variety of 115gr. ammo - Speer Lawman, S&B, Blazer Brass. Zero failures on semi and full auto. It shot very smooth and controllable. My 12 year old had no trouble shooting 4-5 round bursts. The only issue was the bolt hold open would not work - not really a big deal for plinking, but definitely an issue for competitive shooting. I though about trying an H2 buffer to get the BHO working. Any ideas?

 

[Fishman]

Clipping a coil or two off the spring might help it lock back. Testing that is a one way street though.

 

[amphibian]

Made my first trip to the range with RDB CMMG 9mm upper with very good results. I used Amphibian’s setup with the Tubbs flat wire spring, Kynshot 9mm buffer, 2ng gen Endomags, and my SP-1 RR. Shot over one hundred rounds with a variety of 115gr. ammo - Speer Lawman, S&B, Blazer Brass. Zero failures on semi and full auto. It shot very smooth and controllable. My 12 year old had no trouble shooting 4-5 round bursts. The only issue was the bolt hold open would not work - not really a big deal for plinking, but definitely an issue for competitive shooting. I though about trying an H2 buffer to get the BHO working. Any ideas?

I do not have that problem...

Which 9mm Kynshot? There is the RB5007 and RB5015HD.
I recommend the the RB5007.

Bear in mind that both are 'A5' length so if using either buffer with the CMMG RDB setup you need to be using an A5 or equivalent length buffer tube.....If you use these buffers in a carbine length tube then the BCG won't go back far enough for the BHO to catch the bolt....maybe you are using a carbine length buffer tube?

Which Tubb spring? There are 3 different ones. All 3 work but I typically use the 300BLK one as I get about 30RPM slower with that one. 556 one works fine also.

 

[localizer11]

I do not have that problem...

Which 9mm Kynshot? There is the RB5007 and RB5015HD.
I recommend the the RB5007.

Bear in mind that both are 'A5' length so if using either buffer with the CMMG RDB setup you need to be using an A5 or equivalent length buffer tube.....If you use these buffers in a carbine length tube then the BCG won't go back far enough for the BHO to catch the bolt....maybe you are using a carbine length buffer tube?

Which Tubb spring? There are 3 different ones. All 3 work but I typically use the 300BLK one as I get about 30RPM slower with that one. 556 one works fine also.

Using the Tubbs 5.56 spring and RB5007 buffer. Looks like the issue is the wrong buffer tube length. I’ve got a standard carbine length tube on my RR. Need to pick up an A5.

 

[amphibian]

Using the Tubbs 5.56 spring and RB5007 buffer. Looks like the issue is the wrong buffer tube length. I’ve got a standard carbine length tube on my RR. Need to pick up an A5.

You can also go with the RB5005 if you don't want to go to an A5 length tube....however, I still prefer the RB5007.

I think you will also be impressed with same setup with your 556 uppers.

 

[Jmacken37]

I’ve got a Vltor A5 Vulcan ‘blem’ tube for $35 shipped to you if you want it.