I have an RLL that I would really like to use in a 9mm AR. I have held off on using it in a 9mm gun because of fears of breakage/premature wear of the link due to the harshness of the 9mm AR blowback system. Fast forward to today, I just ran across CMMG’s radial delayed blowback system for 9mm. Has anyone used this with a link? Would using this system bring the risk for breakage/wear on the link more in line with that of a link in a conventional AR in .556 caliber? I am using a KNS like protector for my
Ink.

CMMG 9mm BCG
https://www.cmmginc.com/product/barrel-and-bcg-kit-8-4140cm-sbn-9mm/

The CMMG system should work just fine with a RLL after the bolt carrier is properly milled.

In terms of harshness my impression is that the reason 9MM is harder on a RLL is due to the colt pattern setup not having a rotating bolt and cam pin to slow the bolt closing speed before lockup with the RLL.

The Radial Delayed system seems to have that same rotating bolt and cam pin arrangement but I am not sure exactly how the cam angle is cut vs. a traditional 5.56 bolt carrier.  In either regard the CMMG setup should be less hard on a RLL than a Colt pattern setup.

Thanks for the response jbntex. Seems like the CMMG group might be the ticket for 9mm with a link. I really want a 9mm AR with my link but have just had problems accepting what seems to elevates risk of breakage, due to the standard 9mm confit being blowback. It would be great to find someone that has used this type of CMMG radial delayed blowback group with a RLL.

Why not ask CMMG directly?  Their contact information is on their Forum in the Industry Section.

Best of luck with your pursuit.

I will but doubt that they will give me a solid answer. On their website, they don’t even say it is compatible with othe non-CMMG lowers. They obviously aren’t making much in the way of promises....

Get a KNS protector, get your lower milled out properly and get a compatible bolt.   You shouldn’t have an issue with a Colt pattern lower in 9mm, or the Guard in 9mm.

I think they only make Glock magazine version right now.

Do you have experience running a 9mm blowback setup with a link? If the guard option doesn’t work I may just go ahead and roll with a conventional Colt setup.

From what I’ve seen that is correct.

For anyone that is interested, I also posted the question at the link below. In the thread it is mentioned (with a video) that someone is using the guard with an rdias.

https://www.ar15.com/forums/ar-15/Thoughts-on-the-CMMG-Guard-/15-713060/&page=11

I have a Guard running with an RDIAS.  I can say in stock form the Guard runs great after replacing the bolt extractor and ejector springs.  They both seemed weak from the factory at least on mine.  It’s fast and a little harsh though.  Amphibian recommended an A5 buffer tube and the kynshot/blitzkrieg buffer which makes it really nice to shoot.  I have run the RDIAS in both the CMMG Glock lower and a colt pattern 9mm lower with a modfied bolt catch and ASC style plastic follower magazine.  I don’t have the Colt system running perfect yet but it is close and that lower is already an SBR so if I remove the RDIAS and FCG I don’t have to pull the buffer tube and stock. The CMMG Lower is plug and play and I see no reason it would not work great with an RLL after the lower and bolt carrier were setup for it.

I run one of my RLLs with a Colt 9mm setup.   I bought this RLL in 2004 and it has untold thousands upon thousands of rounds through it on a Colt pattern setup (LRM Integrally Suppressed 9MM upper) without issue.

This link has run a protector for as long as I can remember and the full auto disco (modified 3rd burst setup) has a reduced power disco spring so the amount of force to pull the disconnector back off the hammer is greatly reduced.  The lower is properly relieved so there is no binding and the bolt carrier is properly milled so the link doesn't cam backward any more than needed.

I've been playing around with blowback Colt 9mm setups since around 2003.  Using them for SMG competitions and was always disappointed in how choppy they run.  Best I could do was run the LRM suppressed ported barrel setup and an old Olympic Pneumatic buffer which eventually started to leak and was useless.
Always wanted an MP5 as it is in my opinion the gold standard when it comes to smoothness in a closed bolt 9mm SMG.
Now that the 9mm Guard came out, I've been playing with it and so far I'm pretty happy with it.
I got just the 8" barrel and BCG combo and stripped Guard lower.  As mentioned, I'm using a Tubbs flat wire 556 spring, A5 tube and Blitzkrieg/Kynshot hydraulic buffer.  Very smooth.  Very close to a full auto MP5K PDW.  
Note that the Guard carrier accepts the same weight as a Colt 9mm bolt and obviously is machined to trip an auto sear.
Once you get the carrier modified, I don't think you would have any issues running the Guard with your LL.
Unlike a Colt pattern blowback 9mm, I have never experienced any trigger slap with the Guard in any buffer/spring combination I have tried.

I have the original CMMG 9mm bolt. I need to read up on these issues I guess but seems like as long as it is done right, it won't be an issue?

Where does one obtain the reduced power disco spring?

Disconnector Springs - Reduced Power
Wolff Disconnector Springs are aproximately 50% lighter than the factory.  Helps improve trigger function.

https://www.gunsprings.com/index.php?page=items&cID=2&mID=1&dID=79#979

I'm also considering options for my RDIAS.  Will keep up here until I learn more.

Sharing this in case anyone hasn't heard about it yet (in pre-order for $25 each). Thanks again to amphibian for the alert.:

Ingenious!

I spoke with Brian at CMMG and he said the Guard RDB is designed for their lowers and they can't guarantee it will work with others.  He said someone there tried a 3 piece AR-15 mag block adapter with poor results.  Now that amphibian turned me on to the MEAN Endomag and the mag well block adapter issues may be solved (Endomag works will all BCGs) I am itching to try it with the Guard RDB upper.  Brian said they use a standard carbine buffer and a .308 carbine buffer spring with the Guard so we may be gtg with our existing AR-15 carbine buffer and spring.

Would prefer for someone else to try it first though.  

Want this one and I can wait for the suppressor stamp.
Banshee

@amphibian, is that the exact same setup you recommend for your Shrike?

Yes, but need to move up to the 308 Tubb flat spring since the Shrike needs more force to strip rounds off the links.
I've got all this documented with cyclic rates here: http://c3junkie.com/?page_id=654

@amphibian, did you ever have to stretch and/or polish and/or lube your links for the Shrike?

Nope...posted recently about it here: https://www.subgunz.com/boards/mgmsg.cgi?read=72