CMMG RDB LWRC rifle

[MoRivera]

12 hours ago, Les Snyder said:

Mo... I'm running a 5.56 Enidine rifle length hydraulic I pirated from the 3 gun rifle, factory rifle spring (I had previously used a .308 spring with the pre Cmmg blow back bolt, and had some battering to the rear of the boss area around the chamber with a 6.2oz rifle length buffer) both the original blow back and hydraulic with a NFA short bumper to shorten the stroke

Cool.  I'm doing what I can to maintain the LRBHO feature since often I'm limited to 10-rds per mag in my area, so with this excellent info that you and Memphis has shared, I'm really hoping that ejection/extraction will stabilize enough that I can just stick with the H2-equivalent Armaspec Silent Captured in a standard carbine buffer tube.  I've found that with those I get the 'quickness' on the full-length cycle compared to hydraulic buffers alone, same as when I try them with 5.56 rifles, and what moderate short-stroking has done for me in AR9's.  Little less soft on the extreme ends of travel, but the dot bounces back on quicker.

 

I didn't feel like joining up on AR15.com for this (plus, that place seems rather toxic, frankly) so the info in this thread has been really helpful.  Huge thanks.  Will update from my next range test session, and if that goes well, I'll probably shoot it in a PCC match coming up next week.

Edited March 9, 2020 by MoRivera

[MemphisMechanic]

Get the gun reliable then short-stroke it with a few bucks worth of quarters in the back of the tube, until it fail to lock back consistently... and then remove 2 quarters.

 

Short-stroking the gun is the most important thing you can do to flatten out the dot movement, and it also keeps the bolt from getting a running start and slamming into your bolt catch when empty, eventually breaking it.

 

But get it to run 500rounds without a malfunction before you play with that.

 

Edited March 9, 2020 by MemphisMechanic

[MoRivera]

3 minutes ago, MemphisMechanic said:

Get the gun reliable then short-stroke it with a few bucks worth of quarters in the back of the tube, until it fail to lock back consistently... and then remove 2 quarters.

 

Short-stroking the gun is the most important thing you can do to flatten out the dot movement, and it also keeps the bolt from getting a running start and slamming into your bolt catch when empty, eventually breaking it.

 

But get it to run 500rounds without a malfunction before you play with that.

 

Yeah, I do that with my regular AR9's.  Actually had someone make some Delrin spacers when I found out how many quarters I needed.  Also, with my AR9's I use an A5 buffer tube, so it gives me some leeway to fine tune how much stroke length with spacers/wave spring, etc.  I actually already lost a bolt catch which prompted me to go with the spacers.  I have them short-stroked just enough to lock back.  When I put together a 16" OAL upper with the CMMG RDB (waiting for Taccom extensions to be back in stock), I'll be using it on the same PreBan lower I use for my main AR9, and that one has an A5 tube.

 

But for now, I'm using a shorter CMMG RDB upper (with 8" barrel + KVP Linear Comp = 12.5" OAL) on an Aero mil spec lower and carbine buffer tube that I share with a short/suppressed 5.56 AR.  So that's one of the benefits I'm looking to share the Armaspec H2 equivalent since it works so well with the 5.56.  Also, the rearward limit of stroke is already maybe 1/4" behind the bolt catch, so I can't really shorten it with my Blitzkrieg RB5000 in the carbine tube.  But again, in the carbine tube the Armaspec captured gives me that tighter and shorter stroke and less dot bounce than with the hyrdraulic.  In this 'other' firearm configuration, that's fine.

 

But agreed, best to get it running reliably first.  Really hoping the extractor spring upgrade is the key.

[MoRivera]

Did a quick test today, about 200 rounds, each mag fired pretty quickly.  With the replaced extractor and ejector spring, and the Armaspec H2 Captured buffer system.  All went completely smooth without a hitch.  Ejection was very healthy, even on double- and triple-taps fired as quickly as I could.  Have a small local PCC match coming up this weekend that I'll try her through, and I should probably wait 'till about 800+ rounds to really know, but so far it's very encouraging.  Before, I couldn't quite get through two or three mags with the H2 buffer before I'd get a hangup.  The CMMG Pmag inserts ran like a champ.  

 

What's also nice is that if I can stay with this buffer on this braced lower, then its the same that I use with a 10.5"-barreled 5.56 upper, so it really its just a simple upper swiutchout.

 

Have another 8" barrel incoming from CMMG, and when I get an extension to make that 16" OAL (once the Taccoms come back in stock), I'll try it with my preban mil spec lower that I currently run with a Stern Glock mag adapter as a dedicated PCC, and remover the adapter.  That lower has an A5 buffer tube, so then I'll hopefully be able to tune things even more.

Edited March 12, 2020 by MoRivera

[Salsantini]

Update.  Rifle had some issues with longer ammo.  Anything longer than 1.10 would  not feed fully into the chamber due to the short throat.  MemphisMechanic was kind enough to ream the throat of the barrel.  I have tried ammo with 1.125 ol and it feeds great.  

[Salsantini]

On 2/23/2020 at 12:27 PM, Salsantini said:

Les,  I will report back when I get to 1000 rounds.  

Just an update.  I too fell victim to the 1000 round failure to eject.  I contacted CMMG.  They replaced the entire Bolt carrier assembly.  Now the Rifle runs like a champ!