Join TexasGunTalk

300 Blackout Carbine

Discussion in 'Articles & How-Tos' started by Beeg, Oct 10, 2018.

  1. Beeg

    Beeg New Member

    Sep 24, 2018
    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!

  2. Younggun

    Younggun Ginger Avenger TGT Supporter Admin

    Jul 31, 2011
    hill co.
    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.

    Sent from my iPhone using Tapatalk
    jordanmills and toddnjoyce like this.
  3. Gummi Bear

    Gummi Bear Active Member

    Mar 24, 2015
    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.


    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
    outdare likes this.
  4. popper

    popper Active Member

    Apr 23, 2013
    My 18" carbine works fine with umc 220 subs.
  5. W5LF

    W5LF New Member

    Apr 11, 2011
    Dripping Springs, Texas
    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
    Charlie likes this.
  6. Bozz10mm

    Bozz10mm TGT Addict TGT Supporter

    Oct 5, 2013
    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.
    W5LF likes this.
  7. popper

    popper Active Member

    Apr 23, 2013
    Need to run the BCG really wet at first & check the mags for proper operation.
  8. easy rider

    easy rider Slacker Extraordinaire TGT Supporter

    Jun 10, 2015
    Odessa, Tx
    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.
    toddnjoyce likes this.
  9. Leadslinger

    Leadslinger Active Member

    Sep 26, 2010
    el paso texas
  10. Ruger77

    Ruger77 New Member

    Oct 28, 2019
    San Antonio
    Built a blackout pistol an had problems cycling. Used a spikes t2 buffer an it worked perfect.

    jordanmills likes this.

Share This Page