9mm ARs

CMMG, 4" bbl with an SWR Octane 9hd.

 

I am now a running POF 4.5lb trigger. I am loving the feel and performance.

 

Hey everyone, throwing this question out there to see if anyone else has run into this problem:

I am having burst/double fire issues and I think some almost out of battery scares:
build is:
FM dedicated glock lower
glock/colt BCG, cmmg pin/spring (broke original)
Faxon 8.5 barrel
FM 9mm buffer 6.5oz iirc
standard carbine spring, did just install a 308 spring and try again.
LWRC trigger

Thoughts? has anyone here encountered this? and what did you do to fix it?

 

Generally an indication that your trigger and BCG aren't jiving. You're getting hammer follow (trigger resets but then releases as the bolt travels forward, following it forward and striking the firing pin).
Some triggers are known for it, some trigger just don't like some BCG's. It's a lot more common with 9mm BCG's due to their lack of milspec, different shapes, additional weights, etc. I had the same problem with a Triggertech in my Angstadt 9mm AR. Try a different trigger, if you can. There's lots of triggers developed specifically for the 9mm AR platform.

 

Thanks for the reply,
I did order an aim surplus flat blade trigger today, and have a pof from another rifle I could try.

any thoughts on the buffer spring? Some people say standard carbine, some swear by the 308 springs?

 

I have not experimented with buffer springs. Buffer weight is much more important. Not saying springs won't make a difference, but 99% of your dampening and cycle rate will come from your buffer weight (when comparing it to the buffer spring, BCG weight is another large factor due to the blow-back operation). I don't think your buffer setup looks bad, and I don't think it has any relevance to your trigger issue. But, experimenting with a heavier buffer could get you a softer shooting rifle.

 

I think you have 2 options on your buffer spring setup.
1. Buy a proven set-up that is made to go together. Several options. Mine: http://heavybuffers.com/uciw9.html
2. Buy an adjustable buffer and play with it https://www.quartercircle10.com/products/adjustable-pistol-buffer.html & https://www.quartercircle10.com/products/parts-accessories/buffer-spring-xp.html

I am running a 8.5oz buffer with a specifically matched spring and I have NEVER had a jam or double fire

I have run a plain CMMG trigger from their parts kit and a POF drop in...zero issues with both.

Good Luck

 

I use a 308 spring and buffer on mine. I have a Spinta precision BCR and barrel and that's what they recommended. My AR9 has eaten any ammo I can feed her. I just recently installed a Aimsurplus single stage drop in trigger and still have flawless operation.

Have you tried a different trigger just to see if there is any difference? Seems like you already have plenty of weight and spring tension.

 

My Colt AR9 ....

 

Gonna try a few things as soon as I can get to the range, putting in that aim trigger and will bring both buffer springs.

I did weigh my bcg and buffer the other day, came to 22oz which I read is right on.

 

Put a Hogue grip on.

 

Colt DOE clone. protecting nuclear power plants against terrorist attacks in the 80's. also used as transport protection of enriched fuels. folding front sight with flat base to stick through gun ports.
same lower with another colt upper and 10" BCM barrel.

 

If you're looking for the easiest way to convert your AR.

 

Specs?

 

PSA lower
ALG QMS trigger
Spikes mag-block
PRI Gasbuster charging handle
CMMG remped bolt
TROS 5" barrel
AP Custom CF handguard
Spikes ST-9x steel buffer
Magpul grip
Guntec Minimalist stock
Liberty Mystix X suppressor
Primary Arms red dot

 

I'm no ballistics expert but I've heard a lot of people say you get less risk of over-penetration, less noise, and less flash in an HD situation. Maybe others can chime in