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All things 300 AAC BLACKOUT
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 Post subject: Subsonic cycling problem
PostPosted: Tue Jun 12, 2012 6:39 pm 
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I just completed the assembly of my first blackout rifle build and I am having issues with it cycling on subsonic ammunition. I know they are meant to be fired suppressed with subsonics, but my understanding is that with an AAC barrel and gas block it should be capable of cycling subs without a can. My setup consists of an AAC barrel and gas block/tube, Bravo Company auto bcg, Spikes ST-T1 buffer and a Custom carbine center-less ground and polished operating spring made by JP Enterprises. Im thinking that my moving parts may be just slightly too heavy because my bolt is moving back far enough to eject the brass but not quite far enough back to catch the next round, but sometimes it cycles fine. Any advice or suggestions will be appreciated. Thanks


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PostPosted: Tue Jun 12, 2012 8:07 pm 
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I would find yourself a H2 weighted buffer. I have an AAC 9" upper. I used to run and Endine buffer when I ran the Noveske KX3. That was the only way my 7.5" would run. I tried the Eindine on mine without knowing how it would work. My round ejected. The Endine is similar in weight to an H3, but the hydraulics need to be compressed. The subs did not have the umph to do this. I put in a H buffer and it seemed to work fine, but I noticed the AAC manual and several others had better luck or got theirs to work with the H2.

Also remember ejection occurs much sooner on the 300 BLK than with the 556 sytems due to CASE length. I would find an H2 and have a go with that. Also what is the stength of your action spring. How does it compare to a standard M4. Before I went to my rifle class I am in now I replaced my older (3,000 round) action spring with a new Colt action spring and the H2 buffer just to eliminate any possible variables.


Mike


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PostPosted: Tue Jun 12, 2012 9:46 pm 
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So a heavier buffer will travel better with the subsonics? It seems to me that the heavier H2 buffer would make for even worse cycling problems due to a lower pressure but of course Im no expert.


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PostPosted: Tue Jun 12, 2012 9:46 pm 
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The AAC 16 inch upper is designed to use a C buffer and a normal spring. Your spring is probably ok, but your buffer is too heavy.


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PostPosted: Tue Jun 12, 2012 10:21 pm 
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Thanks a lot for the replies guys.

Rsilvers when you say C buffer you're talking about an H1 correct?


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PostPosted: Wed Jun 13, 2012 8:38 am 
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No. An H1 is a heavy buffer. I mean a carbine buffer.


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PostPosted: Wed Jun 13, 2012 4:06 pm 
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Thanks again Mr. Silvers.

My Spikes buffer weighs 3oz and all the other standard carbine buffers I have found weigh 3oz as well. Are there a certain type of carbine buffers yall use? Or should I try taking a weight out of the buffer?


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PostPosted: Wed Jun 13, 2012 5:20 pm 
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An ST-T1 is more than 3 oz.


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PostPosted: Wed Jun 13, 2012 8:28 pm 
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Actually...

http://www.spikestactical.com/new/z/low ... p-707.html


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PostPosted: Wed Jun 13, 2012 11:39 pm 
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If it is in fact 3.0 oz, then it should be good for the AAC 16 inch upper.

But then they are being mistaken about it being a heavy buffer, as the lightest buffer Colt makes is the "C" buffer, and that is 3oz. An H buffer is 3.8 oz, an H2 is 4.6 oz, and an H3 is 5.4oz.


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