300 BLK AR Pistol Build - failure to feed.

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  • ol' poke

    Sharpshooter
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    Jan 14, 2010
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    I'm in the process of building a 300 BLK AR pistol. Since I finished this pistol, I've had failure to feed/eject issues.

    First, the specs:
    The lower is an 80% build with BCM trigger group.
    The upper is a Ghost Firearms 10.5" Elite with their Titanium Nitride BCG.
    Buffer tube & spring are from Midwest Industries.
    All mags are 20 and 30 round Gen3 PMAGs.
    All ammunition is factory-made.

    I first started off using supersonic MacTech 123gn ammo. This ammo worked flawlessly.
    I then switched to subsonics (Remington 220gn AMAX, American Eagle 220gn, Hornady Black 208gn)
    At all of the subsonics are either not fully ejecting the empty cartridge, or ejecting the fired cartridge, but not bringing the bolt back far enough to pick up the next round.

    So I'm thinking my buffer spring was too strong. This sounded logical, so I switched the buffer spring out for a NEMO .300 BLK carbine buffer spring.

    Now, with the NEMO spring, after the first round is fired, the next round is stripped from the mag, but the BCG does not fully get into battery, about 1/4-1/8" short. The forward assist won't budge it, and its a PITA to extract. Almost like this spring is not powerful enough to fully chamber the next round? But I don't know why its locking up so tight.

    Anyone have any suggestions to make next? I have a call into Ghost to see if they have any comments, but thought I'd see what INGO says as well.


    Thanks in advance.
     

    deo62

    Master
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    Apr 8, 2009
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    For what its worth, I had a plugged gas tube on a new build. Process of eliminating and came down to tube had corrosion in it. Ordered new tube and tada!
     

    ol' poke

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    I considered an adjustable gas block, but have one concern. If the gas port in the barrel itself is undersized, will the adj. gas block even matter? If it was set wide open, the problem would still exist. So two more questions: what should the gas port on the barrel measure at? And how might the buffer weight be adjusted to correct my symptoms? In the meantime, I'll remove the gas block and check for any blockages. Anything else to check?
     

    NyleRN

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    The subs don't have the power to fully cycle the bolt. That's why it'll run fine on full power stuff. Put a suppressor on it with subs and it'll run fine as is
     

    NyleRN

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    I considered an adjustable gas block, but have one concern. If the gas port in the barrel itself is undersized, will the adj. gas block even matter? If it was set wide open, the problem would still exist. So two more questions: what should the gas port on the barrel measure at? And how might the buffer weight be adjusted to correct my symptoms? In the meantime, I'll remove the gas block and check for any blockages. Anything else to check?

    Messing with spring and buffer weights help with getting the correct timing. The heavier buffer and stiffer springs delay the unlocking of the bolt from the barrel extention. That's really one of the purposes of the spring/buffer. But I understand that folks mess with those things to help slow down bolt bounce and tame recoil
     

    jinks

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    Aug 5, 2013
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    I purchased a DSA and a PSA .300 Blackout upper when they first came out. I had similar problems using a H2 buffer. I lightly polished the chambers and changed to to a standard carbine buffer to fix the problem. I am able to shoot supersonic and subsonic cartridges without problems.
     

    edwea

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    Jan 25, 2015
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    New Dolan
    I had the same issue on a 300 blk pistol build. I discovered that the gas block wasn't perfectly aligned with the gas port. Fixed that and still had some feed issues. Added rubber insert/o-ring to extractor spring and voila! Now runs 100%.
     

    BiscuitsandGravy

    Future 'shootered'
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    Nov 8, 2016
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    At the Ranch.
    Here is quick check... how many round have you ran thru your 300? Make sure your bolt moves freely in the BCG and gas rings are not full of crud. Those rings take a lot of abuse. YMMV.

    Otherwise, it sounds like a gas issue.
     

    Scuba591

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    Jan 22, 2013
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    The op is having cycling problems, I'd look for an upper than doesn't require changing parts to make it work properly.


    Thanks for pointing that out:):
    I was more interested in knowing from the OP, what he thought of the fit to the lower, the finish of the upper... less of how it is running
     

    ol' poke

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    Jan 14, 2010
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    Thanks for pointing that out:):
    I was more interested in knowing from the OP, what he thought of the fit to the lower, the finish of the upper... less of how it is running

    If fit and finish were more important than functionality, I'd be ecstatic. I got the burnt-bronze finish and the titanium-nitride (gold-tone) BCG. It looks truly B.A. with the black lower and furniture. The barrel was centered in the shroud, unlike a post I read somewhere earlier where theirs was canted. Matches up completely with my lower.

    Now if I could just get this thing to run consistently with subsonics, I would be a very happy man.
     

    BiscuitsandGravy

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    This is always a PITA but you could measure the diameter of the gas port... If its on the small side, you could always open it up. Assuming your gas block is already aligned and no gas leaks... Just saying... YMMV.

    :ingo:
     

    jimmothy86

    Plinker
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    Jan 29, 2010
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    Indianapolis
    Why do you have to use a suppressor with subs? I mean, I understand the two go hand in hand and using one without the other is basically a waste, but does the suppressor actually add the feedback pressure needed to move the gas when subs are used or is it just a best guess?
     

    NyleRN

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    Dec 14, 2013
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    Why do you have to use a suppressor with subs? I mean, I understand the two go hand in hand and using one without the other is basically a waste, but does the suppressor actually add the feedback pressure needed to move the gas when subs are used or is it just a best guess?

    Yes, suppressors add back pressure. Some more than others depending on the design
     
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