There was an upper made for the AR-15/M16 that had a ported barrel that used a standard SD can and was blowback operated. The upper was called a LMR-169. If you are interested, http://www.silencerresearch.com/lrm_m169_review.htm is a review from 2007. It would be cool to update the system with the CMMG rotary delayed blowback system. It could be done, but would not be cheap. I could see $1,500 to $2,000 in the ported rotary delayed blowback system modified parts to make such an upper unless you can do the work yourself. It is my understanding that the rotary delayed blowback system doesn't like being suppressed. I wonder if a ported barrel with fit with the radial delayed blowback system better.

Scott

The only time I had issues with suppressing my 9mm RDB is with the spring loaded weight I put in the carrier.
For 9mm, I'm not using that anymore.
I have seen about a 60RPM increase when going suppressed.

I now run a 40SW RDB bolt for 9mm use to delay the bolt more for suppressed usage.

Regarding the LRM169, I have one of those and was just about to get it rebuilt for the CMMG RDB system but stopped when I heard about the MEAN Arms roller delayed coming out.  I'd like to see how that pans out first.

The big question for me, as far as the MEAN roller delayed system, are they doing different locking peices like the HK system? What are they going to have for barrel lengths? Are they going to do a SD upper? Personally I would make an upper that uses modified HK style barrels, trunnions, and bolt groups.  Why reinvent the wheel when the HK style parts are off the shelf components? I think that the MEAN concept is cool but it needs so many custom parts, if you want more than a 9" or 16" barrel lengths. What about a K length, K length with a suppressor or an SD? Are they going to do some of those configurations? What about  .40 caliber? That would make feeding it from an AR magwell more complicated. It is so expensive to make custom parts. At least that is my perspective.

Scott

I have an LRM M16/9 upper I got direct from Lee probably 15 years ago.  Overall its been a great integrally suppressed upper, although it is sealed and aluminum, so cleaning options are limited.

Given the way its ported its honestly pretty soft shooting even though it is direct blow back.   If you wanted to adapt it to one of the new delayed breach AR15 9MM pattern guns you would just need a barrel and to have it threaded.

The M16/9 barrels are different from most SD style barrels where the threads for the suppressor are at the rear/breach end of the barrel.  On the LRM M16/9 the threads are in a more traditional barrel placement at the muzzle end (1/2x20 if I remember correctly) and the suppressor has the threads on the rear of the monocore which creates the front of the expansion chamber.

The good news in this proposed M16/9 conversion is that one of the limitation on creating an SD style barrel with an SD pattern suppressor is there needs to be enough material on the barrel just forward of the breach for the traditional M18x1 SD thread pattern and also still have enough material for some sort of shoulder for the suppressor to mount up against. This isn't the case with the LRM M16/9 being a tradition muzzle thread suppressor attachment arrangement.

I actually had a similar thought on upgrading my LRM M16/9 upper when CMMGs delayed rotary setup came out.   However, based on my experience, the CMMGs rotary design is crap for NFA use and the handful of folks I know who have them have either just abandoned them into the scrape pile or just suffer with continuously replacing the ejector springs.   Maybe the CMMG system works for your average semi-auto owner who doesn't put more than 1000rds down the pipe in their lifetime.  But run that system hard in full auto and suppressed and the weaknesses become immediately apparent.   The CMMG system also in standard form isn't as smooth as the MP5 either (although I know Amphibian has ton a ton of mods to get it on par with an MP5) so the upside to moving to that system is a bit more limited.

Similar to Amphibian, I am waiting to see how the mean arms roller delayed system works out but honestly there isn't a huge difference in my opinion between the recoil impulse of the ported blowback LRM M16/9 and the CMMG system in stock form.

That said if I can turn my LRM M16/9 into an MP5SD (which is the softest shooting subgun gun I down) via the Mean roller delayed system without a huge drop in reliability I will probably consider upgrading at that point.

Been there, done that.

I have not done a write up, but here is quick description. I used a CMMG Barrel/BCG and Upper. I used Midwest SD HG. I had Class3 machine the barrel, I had a spare MP5SD barrel so he was able to profile it exactly. Right now I am using the CMMG mag conversion, so I can put it on my M16 lower. Eventually I will do a Glock lower.

Currently the gun is getting cerakoted. I will post pix and video when I get it back. I only put 90 rounds through it to test it before breaking it down and sending it out for cerakote. It ran 100%, had no blowback, and ROF was a bit faster. I tested it with both B&T an TPM silencers.


Attached File

That is a really cool project. I was actually thinking about doing something just like this. I'm looking forward to seeing the completed gun!

Having never owned one myself, I thought that the LRM-169 was a blowback 9mm upper that had a ported barrel and used a HK SD can.  Is that not the case? I own multiple clones of the HK SDs and multiple SD style suppressors in a couple of calibers.

It would seem to me that the easiest way to actually make a SD style upper would be to start with a clone SD barrel like  https://rimcountrymfg.com/?s=Sd+Sd+barrel+&post_type=product and thread it for the barrel extension. So the barrel could be used with an AR upper and the CMMG Guard rotary delayed blowback bolt group. A standard barrel nut could be installed and a plate could be fabricated that the SD can could seal against. If the plate could be thick enough, a groove for an O-ring could help keep the SD can in place. With the diminished power of the ported barrel would be easier on the ejector spring.

Scott

ETA The SD rotary delayed blowback upper is very cool. Thank you for sharing. What did the project cost?  I am very much looking forward to the pictures.

The first two attributes are correct.   It is a Colt patten blowback upper and it uses a ported barrel which acts like an MP5SD barrel in that it bleeds velocity off to subsonic (although not as aggressively.  My german MP5SD runs about 980fps with 115gr ammo, my LRM upper runs abiut 100fps faster at 1080).

However the method of attachment of the suppressor to the barrel is completely different.  The HK pattern has the threads at the rear of the suppressor, the LRM has the theads at the tip of the barrel and the coresponding female theads at the end of the expansion chamber.

My MP5SD and MPXSD can share suppressors both being HK pattern.   My LRM AR upper and Smith76 both have proprietary threads/attachment methods.

An MP5SD barrel will not fit. There just is not enough length to go from the breech to where it would clear the barrel nut.



Barrel work cost me $150. Other parts are whatever you need and have to buy.