300 blackout not cycling

Tackleberry

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Dec 16, 2005
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I have a AAC 300 blackout upper (16") on a standard Rock River lower with a A2 stock. I have the bolt carrier group well lubed running southwest subsonic 220's. I have tried a pmag and a rock river 20 round mag and it still fails to cycle. Do I need to change buffer tube or springs? Thoughts or ideas?
Thanks
 

mscott

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I'd try different ammo if you can. Is it a pistol or carbine length gas system? How is it not cycling? Are you using a can?
 
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Tackleberry

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It's a factory standard 16" AAC complete upper. I have also tried remington subs. A few will feed other times it just fails to feed the round. It could be an issue with the mag or mag lip as well. Very new to shooting subs in a ar platform. I know very little about gas guns
 

mscott

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Sounds like a good ejection pattern, so I'm guessing the powder burn rate just isn't enough to cycle the gun. I wonder if they are using H110 for that ammo? Are you running a suppressor? My 9.5" pistol gas will run subs without a can, but my 16" carbine gas is a little more finicky. I'm also reloading using A1680 powder.
 
G

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We use AA 1680 as recommended by AAC, and test fire each lot in the same 16" upper that you have with Pmags. AAC advises the use of a standard carbine buffer, a heavy buffer may be your problem.

Give us a call at the shop, and ask to talk to me, and we'll figure this out.

Thanks,

Mike


Sent from my iPad using Tapatalk HD
 

WRH51

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Are you running a can? Does that upper have an adjustable gas block? I know some set ups are intended to run subsonic suppressed only.
 

Tackleberry

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I do have it on a A2 stock. I removed the rifle buffer and put a carbine buffer in. Fired 5 rounds in the back yard and seems to work. When the rain stops I will take it out and fire a magazine and see how it works for real. 5 in the ground in the back yard is only a tease.
 

usmc45

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Check your buffer spring as well. Make sure it is a "TRUE" milspec.........I had an issue and it was the BCM buffer spring I was running.
 

mscott

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I don't think you want to run a carbine buffer in an A2 stock without a spacer. There is a reason buffers are a certain length.
You can lighten up your A2 buffer by taking it apart and replacing the steel weights with aluminum weights.
 

kaotic504

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i think the subs were designed to run w/ a suppressor. are you running it suppressed? supers will probably cycle it. but i agree w/ everyone else, it's the buffer.
 

Tackleberry

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Got the suppressor. The whole thing is no good without it IMO. Carbine stock kit coming today or tomorrow. Hopefully she will cycle rapidly
 

TexasMade

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My buddy has a Blackout and tried everything, we finally put a JP Buffer in it because its "self adjusting" and sure enough it worked, and on another note it sounds like butter when you pull back the charging handle
 

Ron

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I'm having a problem with my 300 blackout as well, i'll fire 5 rds. but the bolt does not lock back, it cycles on a empty mag. i have a 16" black hole barrel carbine length gas system blow back. carbine stock wth a standard carbine buffer and buffer spring, sometimes the bolt will lock back but most of the time it dose not. plus i'm using a jp interprise adjustable gas block.
i am stumped !!this gun is giving me fits.
is the gun over gasing or is the buffer to heavy? what would be a god light buffer and what buffer spring would work?
please hepl!!!
 

The Lawn Ranger

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I have a 10.2" Noveske that won't lock open after the last round with some factory ammo types.

Loading my own solved this.

Mine is without adj. gas block
 

gaphighpower

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I had similar problems during my build.

My build:
Wilson Combat 18” upper – straight gas, not adjustable
Stiller Precision PredatorXT lower
Standard milspec receiver Extension Kit – standard buffer
Magpul CTR Mil Spec Stock

I reload my 220s:
Sierra 220 HPBT match
9.0g LilGun, in mixed brass

I run a SHARK suppressor ALL THE TIME with 220s.

Everything I shot under 220g runs great with the above specs (with or without suppressor), but when I started shooting the 220’s the problems started.

The two modifications I made to run 220’s smoothly:

1) I used a shorter buffer spring (see pic) 10.75” vs. 11”
2) Check your mag(s). Load 3-4 rounds. Notice the ogives’ and large footprint of the 220 to be radical for a magazine designed to shoot .223 bullets. Press down into the follower. Do you notice binding when you push down? Can you manually push a round out (feed) with the next round rising smoothly and correctly into the lips and not binding in the mag? I found binding in all the mags I had – plastic and metal. This caused the bolt group to ‘ride over’ a round that would not rise to the correct height in the mag. I got out the dremel tool and removed the ‘rib’ portion of a metal 20 rounder (see pic). The 220s feed butter smooth now and I have smooth function from first round to last.

Of course, YMMV.

Hope this helps,
gap
 

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jake6547

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same problem here with suppresor, I cut 3 coils off the buffer spring and now it runs perfect! cycles and locks back every time. I also have a MGI heavy buffer and I swear when I added it the gun got quieter. Does that make since?