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300BO Pistol Setup?

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  • mtbbrewer74

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    This is a Pistol setup with a Pistol gas system.

    - 9.5" barrel

    - Pistol Buffer Spring/Carbine

    - Standard Carbine Buffer

    - Griffin SNACH 15 Charging handle

    - Toolcraft Nickel Boron (AR15/M16) BCG

    I mentioned this in a previous post, but I decided to make it it's own. First time out with this pistol it was flattening the end of the shell casing with Supersonic ammo. I got the impression from some of the responses that this is common on 300 BO. I was told I need to shoot Subsonic next to see if it would cycle, which is where I come to my next issue. With Subsonic it will fire, and eject the empty casing. However it doesn't cycle far enough to reset the trigger. Do I need a lighter buffer or spring?
    e422062f3fa888d719aca274dc8b3be6.jpg


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    SAWMAN

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    How far to the rear does the BCG have to travel to "reset the trigger" ?? Give it a try. Slowly pull back on the charging handle. --- SAWMAN
     

    m4a1sof

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    Mine does the same thing to the case mouth. I have no issue with the subsonic not pushing the bolt back far enough though, either with or without a can attached. I use an H2 buffer and a standard spring.
     

    Little Jack

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    There are lots of combos in ammo, buffer, spring and gas port. Personally, I don't want my setup to cycle subs without a can. If a gun is going to cycle subs without a can, it's over gassed. But to each their own.

    If you want it to cycle completely without a can, lighter buffer/ spring or more gas.

    What's the ejection pattern like with the super?

    I've got various guns that will ding the case mouth. 300 and 5.56. Unless the recoil is excessive. I wouldn't worry too much.
     

    Daezee

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    Flattened case mouth on Blackout is normal...that is where the spinning/ejected shorter case hits the brass defector. Since an ejecting .223/5.56 case is longer, it hits the defector more towards the side of the case rather than the mouth. One might put some velcro on the case defector in an effort to reduce the flat spot, but your sizing die will remove it. Don't worry about it; I don't.

    Regarding shooting subsonic:

    Subsonic ammo, by its very nature of using less powder to achieve less velocity sometimes doesn't have enough oomph (gas port pressure/gas volume/or gas dwell time) to fully cycle the AR action if a suppressor is not in place. A suppressor increases the dwell time of the gas on the AR system (keeps the gas pressure up a little longer, giving more time for the gas to act on the system). You don't mention using a suppressor. You also don't mention your subsonic ammo...is it a reload? If a reload, maybe the powder used is not producing enough gas. Example: H110 is used by many Blackout reloaders for supersonic loads, but sometimes doesn't produce enough gas volume for subsonic; AA1680 is often used for subsonic, as it is slightly slower burning and gives more gas volume.

    It may be with more break in of the moving parts and generous lubing that subsonic will function property. A good test is load only one round in the mag and fire. Did it have enough oomph to lock back the BCG on the empty mag?
     

    m4a1sof

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    I use this chart to tune all my various caliber AR's:
     

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    mtbbrewer74

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    There are lots of combos in ammo, buffer, spring and gas port. Personally, I don't want my setup to cycle subs without a can. If a gun is going to cycle subs without a can, it's over gassed. But to each their own.

    If you want it to cycle completely without a can, lighter buffer/ spring or more gas.

    What's the ejection pattern like with the super?

    I've got various guns that will ding the case mouth. 300 and 5.56. Unless the recoil is excessive. I wouldn't worry too much.
    Yeah I am not worried about the casing on the Supersonic. I won't worry about making any changes until I get the suppressor, and re-try. If I am lucky that will be the end of May 2020.

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    Rebel_Rider1969

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    I'm going to shoot mine today. If it won't cycle the subs I will put this on and see. Only thing is don't know how if any effect it will have on the supers. I used this to solve my 7.62x39 ar's issues using a 7.5 inch barrel.

    20190925_201348.jpg
     

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    Daezee

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    Testing I've done with the Noveske Flaming Pig, Spike's Barking Spider, Kaw Valley linear comp in a 7.5" 5.56 bbl indicate they increase the back gas pressure on the operating system.
     

    Rebel_Rider1969

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    I'm going to load 1 subsonic and shoot without the baffle installed to see if it will cycle and lock open. If it does I' may put the birdcage back on it. If it doesn't I'll put the baffle on and try it. I don't need the extra pressure for the supers and don't want to hammer the $hit out of the poly action. Just my random thoughts.
     
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