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300 Blackout Carbine

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  • Beeg

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    Sep 24, 2018
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    MN
    I recently purchased a 300 Blackout carbine. Right out of the box I started having trouble with subsonic rounds not reliably ejecting the casing and not picking up the following round. I have learned that the 300 BLK pistol barrel "gas port" is around 7" fro the breach and the carbine is around 11". This difference doesn't allow the subsonic to create enough back pressure to fully recharge the bolt. I'm told that a suppressor might create enough back pressure to shoot subsonics? Does anyone out there agree with this?
    Next question: I can buy a carbine barrel with a pistol gas port. Does this created a problem with shooting supersonic rounds??? The twist is 1:7 on a carbine barrel and 1:8 on the barrel drilled for the pistol gas port. Is that a problem? I appreciate any knowledge on this!
    DK Firearms
     

    Younggun

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    Jul 31, 2011
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    Yes, a carbine length gas system can be finicky with subs.

    Yes, a suppressor can help with cycling issues. Depending on the gas port size you may still have problems but it sounds like you don’t need much, just a hair more to get it cycling.

    A pistol length system would probably fix the issue. The cartridge was designed around a short barrel and suppressor.

    Yes, a 1/8 twist will be just fine.

    There are also a few things you can do to help your rifle function with subs.

    First, get heavy subs. The heavier the bullet is, the more gas pressure it will take to push it while remaining subsonic. What weight were the Subs you were using?

    You can order an extra buffer spring (cheap) and clip a few coils off. Go a little at a time and only trim what you have to. Get it too short and it won’t drive the bolt carrier forward with enough force. It could also cause the buffer to start battering against the buffer tube which is hard on everything. Especially when you switch to supers.



    All that said, I don’t see much point in shooting subs if they aren’t suppressed. You loose a lot of punch for hunting, the ballistics are kinda crap, and bullets that will expand become fairly expensive.


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    Gummi Bear

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    Mar 24, 2015
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    My rifle is carbine length, and it cycles everything. My buy built an identical rifle (just different furniture) and his is flawless as well.

    We drilled our barrel to .125” (YHM low profile gas block)

    I have a rifle length stock, and use a carbine spring and buffer (I cut and fit a dowel into the buffer tube, so the length is the same internally)

    I primarily shoot supersonic, and hunt with it all the time.

    83a4e890c4915ad747063bc5c488ca76.jpg


    Since this picture (4-1/2 years ago), I’ve added a suppressor. The last year or so, I’ve been having some fun stretching it out. I shot a pig at 300, and a coyote the next morning at 310, one shot each.




    I went to the woods because I wished to live deliberately...

    Henry David Thoreau
     

    Bozz10mm

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    I am going to purchase a .300 blackout upper for my AR15 upper, which less expensive uppers anyone has good success with? I will add a suppressor later
    I am very satisfied with my CBC Industries 300 Blackout upper. I have a little over 500 rounds through it without any FTE or FTF with supersonic ammo. Have not tried subs with it. I paid about $100 more than they are listed for here on sale.
    They don't come with BCG or CH and it looks like they only offer key mod handguards. But for only $199...
    Life time warranty and free shipping included.

    https://www.cbcindustries.com/collections/upper-assemblies/
     

    popper

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    Need to run the BCG really wet at first & check the mags for proper operation.
     

    easy rider

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    I have to agree with Younggun. When I built my 300 blk (carbine length) I found that there were many comments of issues with a rifle length or carbine length gas tube in using subsonic and elected to go with the pistol length. I don't have a suppressor for it, but I didn't want to limit that possibility.
     

    ZX9RCAM

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    I recently purchased a 300 Blackout carbine. Right out of the box I started having trouble with subsonic rounds not reliably ejecting the casing and not picking up the following round. I have learned that the 300 BLK pistol barrel "gas port" is around 7" fro the breach and the carbine is around 11". This difference doesn't allow the subsonic to create enough back pressure to fully recharge the bolt. I'm told that a suppressor might create enough back pressure to shoot subsonics? Does anyone out there agree with this?
    Next question: I can buy a carbine barrel with a pistol gas port. Does this created a problem with shooting supersonic rounds??? The twist is 1:7 on a carbine barrel and 1:8 on the barrel drilled for the pistol gas port. Is that a problem? I appreciate any knowledge on this!

    Welcome to the Forum!
     

    Charlie

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    'Top of the hill, Kerr County!
    I've got a friend and fellow forum member that wants to do some trading so he can put together a pistol. And would have made the swap before now if it wasn't for all this beercrap disease going on. The AR pistol just doesn't have the charm it used to! :green:
     

    Texasmade94

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    Jun 9, 2020
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    Dallas
    I am very satisfied with my CBC Industries 300 Blackout upper. I have a little over 500 rounds through it without any FTE or FTF with supersonic ammo. Have not tried subs with it. I paid about $100 more than they are listed for here on sale.
    They don't come with BCG or CH and it looks like they only offer key mod handguards. But for only $199...
    Life time warranty and free shipping included.

    https://www.cbcindustries.com/collections/upper-assemblies/

    Hey Bozz, i know this forum is a little old but just came across it. How is the CBC upper still running? Could not find much in terms of reviews (good or bad), but there was a healthy mix of the ones I did find.

    Just passed on one and went with the GHOST rifles/grid defense. was $229 on sale. But was looking at CBC for 9mm build I wanna bust out next.

    Thanks!
     

    Bozz10mm

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    Oct 5, 2013
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    Hey Bozz, i know this forum is a little old but just came across it. How is the CBC upper still running? Could not find much in terms of reviews (good or bad), but there was a healthy mix of the ones I did find.

    Just passed on one and went with the GHOST rifles/grid defense. was $229 on sale. But was looking at CBC for 9mm build I wanna bust out next.

    Thanks!
    The CBC 300 Black Out upper has been flawless. I'm happy with it. It matched right up to a Palmetto State Armory lower. Admittedly, I don't have that many rounds through it, approximately 504. Accuracy is acceptable with Nikon P 223 1-3x 32mm scope.
    IMG_2139.JPG
     

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    bignic83

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    Mar 29, 2014
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    I have 10.5" SOLGW barreled 300 Blackout SBR. I run Hornady Black 208 grain subs and have never had an issue. I also run a Liberty Cosmic can on it so that may help. I believe the SOLGW Barrel is made by Ballistic Advantage but not sure. IMG_3308.jpg
     

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