Pennsylvania Firearm Owners Association
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  1. #1
    Join Date
    Oct 2007
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    Moscow, Pennsylvania
    (Lackawanna County)
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    Default 300 Blk pistol built barrel/gas question

    Searched the net for an answer, to no avail. Not new to building AR rifles, but this one has me stumped: 300 BO pistol build, with 13.5" barrel (I found a great price on barrel), with carbine length gas system....will it work okay without diddling with buffer weights and such? No info available on gas port size from manufacturer.

    Everyone says go with pistol length gas, but I'm only ever going to use supersonic ammo with cast bullets (or pulled 147 gr. bullets). Not going to ever use a suppressor on it. I know supersonic ammo over-gasses the pistol length gas system. Just wondering if anyone here has built/run a 300 BO with under 16" barrel with CAR length gas system, and if there are any hidden issues using supersonics with it?

    Currently have a 300 BO AR rifle, with no problems with CAR gas system, using reloads with 147 grain FMJ reloads. Just can't find anything on if there is problems with pressure drop-off too fast in 13.5" barrel using CAR gas system to give proper functioning.

    Considering this as my "Winter Build" pistol, that possibly will turn into an SBR once pistol works and paperwork gets approved.

  2. #2
    Join Date
    Feb 2015
    Location
    Bristol
    (Bucks County)
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    Default Re: 300 Blk pistol built barrel/gas question

    You shouldn't have a problem at all with that set up, buffer and everything will be fine with supersonic ammo. The only time I had problems was after deciding to buy a suppressor to run with my 10.5" build with a CAR gas system. I originally was only planning to shoot it unsuppressed so I didn't care about the gas system, no problems with supersonic ammo. Running subsonic with and without my suppressor it was short stroking. It was easier for me to swap the barrel for a pistol length to fix the problem with subsonic ammo then to play with a nemo spring or buffer weights. If you think you may decide in the future to buy a suppressor, I would just buy a pistol length gas system now.
    Last edited by :-); August 31st, 2018 at 04:04 PM.
    -Smiley IANAL, don't listen to me.

  3. #3
    Join Date
    Oct 2007
    Location
    Moscow, Pennsylvania
    (Lackawanna County)
    Posts
    183
    Rep Power
    8058123

    Default Re: 300 Blk pistol built barrel/gas question

    Quote Originally Posted by :-) View Post
    You shouldn't have a problem at all with that set up, buffer and everything will be fine with supersonic ammo. The only time I had problems was after deciding to buy a suppressor to run with my 10.5" build with a CAR gas system. I originally was only planning to shoot it unsuppressed so I didn't care about the gas system, no problems with supersonic ammo. Running subsonic with and without my suppressor it was short stroking. It was easier for me to swap the barrel for a pistol length to fix the problem with subsonic ammo then to play with a nemo spring or buffer weights. If you think you may decide in the future to buy a suppressor, I would just buy a pistol length gas system now.
    Thanks for the info. I couldn't wrap my head around the pressure issues with barrel length vs gas tube length. Wasn't sure if the gas port-to-muzzle distance made any difference in the pressure curve.

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