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Posted: 4/21/2014 7:12:57 PM EDT
Hey all, got a 9mm AR that I put together and it's not really working right.  

Specs:
RRA complete upper with bolt
CMMG dedicated 9mm lower
RRA 9mm buffer with a 6 position buffer tube with no name spring

Issues I'm having are FTE and stovepipes.  Now this was the first time I took this rifle out and I put about 200 rounds through it using 4 different kinds of mags, having issues with all mags.  It seemed to be about every 4th shoot would FTE and jam up the action.  I even had one make it back over the bolt, down through hammer hole.  Most of the time, it wouldn't eject and would pull the next round out of the mag and then jam the spent case above the chamber.  I'm kinda stumped at this point.  But one a good note, when it did shoot, it was great.
Link Posted: 4/21/2014 7:32:30 PM EDT
What type of mags?  Maybe the feed lips are opened up too much? Or the spring is too weak?

The only issues I ever had with mine was the c-products mag block. But if you have everything dedicated and made for it, plus the heavy buffer, I would think it has to be mags or spring.
Link Posted: 4/22/2014 2:48:45 AM EDT
[Last Edit: 4/22/2014 2:49:24 AM EDT by faawrenchbndr]
Originally Posted By DaSandmanCometh:
Hey all, got a 9mm AR that I put together and it's not really working right.  

Specs:
RRA complete upper with bolt
CMMG dedicated 9mm lower
RRA 9mm buffer with a 6 position buffer tube with no name spring

Issues I'm having are FTE and stovepipes.  Now this was the first time I took this rifle out and I put about 200 rounds through it using 4 different kinds of mags, having issues with all mags.  It seemed to be about every 4th shoot would FTE and jam up the action.  I even had one make it back over the bolt, down through hammer hole.  Most of the time, it wouldn't eject and would pull the next round out of the mag and then jam the spent case above the chamber.  I'm kinda stumped at this point.  But one a good note, when it did shoot, it was great.
View Quote



Start with trashing the "no name spring"
Inspect and replace the extractor if needed
Link Posted: 4/22/2014 7:40:55 AM EDT
Is your bolt ramped?  If not, it will not work with the standard hammer in the CMMG lower.  You would need to either used a ramped bolt or install a "notched" hammer in the lower.
Link Posted: 4/22/2014 7:43:13 AM EDT
[Last Edit: 4/22/2014 7:49:27 AM EDT by wildearp]
I had the same setup, same issues.  Buy a sprinco heavy spring and a Spikes ST-T2 buffer.  It will then run just fine.  Don't do anything else until you do these things.  It really makes me wonder what RRA ships in their complete rifles.

Mine had the hardest time with 147gr bullets.  115 and 124 ran fine after the changes.  I still haven't gone back to the heavy subs to see if they run. The fucker is a bullet hose now.  6 mags will spray out like a paint gun.    In the height of the ammo crisis, I am sure the guys at the range thought I was pure crazy.  I would just show up, spray out 6 mags in a couple minutes and leave.  

My fail to eject was really mangling my brass. The jams were hideous.  The bolt was simply cycling too fast the cases would not eject properly.  

Adco ramped my bolt and shortened the barrel to 10.5" before I started on this project.  I used the mag block RRA ships and started out with Uzi mags.  I learned that the bolt hold open was a good feature and changed to Metalforms.  Now the Uzi mags are collecting dust.
Link Posted: 4/22/2014 9:40:09 AM EDT
Check your ejector too, sometimes they need to be adjusted to run as close and as high up on the bolt face as possible. If there's too much gap between them the case head won't strike it properly and won't clear the ejection port properly. If you google search 9mm AR15 ejector tuning you should find a picture someone made a while back that illustrates it quite well.
Link Posted: 4/22/2014 12:49:08 PM EDT
Did you do the BHO modification?  If not your bolt could be binding on it and slowing the whole works down.  RRA bolts don't play well with the CMMG dedicated lower unless you take a mm or so off the top right side of the bolt catch.
Link Posted: 4/22/2014 8:36:16 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By 226man:
Is your bolt ramped?  If not, it will not work with the standard hammer in the CMMG lower.  You would need to either used a ramped bolt or install a "notched" hammer in the lower.
View Quote


Are you telling him that he needs a "notched" hammer if his bolt is un-ramped?
Link Posted: 4/27/2014 2:01:16 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By Imdelaw:
Did you do the BHO modification?  If not your bolt could be binding on it and slowing the whole works down.  RRA bolts don't play well with the CMMG dedicated lower unless you take a mm or so off the top right side of the bolt catch.
View Quote

Could you show us exactly where your talking about, I have this combo and same problem, thanks
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