Of SBR's and gas port sizes

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts
  • Jefr00
    Unwashed
    • Aug 2016
    • 3

    Of SBR's and gas port sizes

    Ok, so here is the setup. I have a Sabre Defense M4 upper, 16", carbine gas, stock carbine spring and H buffer (the spring and buffer can certainly be replaced). I am trying to decide to what length I want to cut it back to, 14.5" or 10.5". I plan to run it with my Rugged Surge .30 cal suppressor. Not wanting to run anything other that the stock front sight base. I want to preserve the M4 look and configuration.

    Any idea as to what the stock gas port size is? What are thoughts on the size of the port based upon the above specs? I've been crawling all over the internet looking for data, and the results have been mixed. I read an old post by Bill Alexander stating that .073, for a 10.5, was advisable, but that was for a non-suppressed gun. I've read some other postings for the 10.5 running with a range of greater than .073 into the .080's.

    In regards to the 14.5", would the gas port need any work at all? How big a deal is it to remove 1.5" of barrel?

    Any advice would be greatly appreciated.
  • bigdaddyflo
    Bloodstained
    • Dec 2016
    • 97

    #2
    I have the following barrels in hand and have measured the gas ports for each one.
    20" barrel - rifle length tube - gas port is .090"
    18" barrel - mid length tube - gas port is .080"
    16" barrel - carbine length tube - gasport is .060"
    The group buy barrel is 12" - carbine length tube - the gas port is undetermined by me but others may chime in that have one in hand (I don't have one in hand - yet)
    Either way, I am putting an adjustable gas block on all of them since they will all be suppressed and will have to be fine tuned to shoot my preferred round.
    If you're removing 1-1/2" you should be fine with your stock set up. Now cutting the barrel to 10-1/2" you may have to change the buffer since you can't do much with the gas port and will probably be overgassed. You may also have to go with an adjustable gas block, but don't know for sure - depends on your current gas port dimension.
    Either way, keep us posted on your project.
    Good luck!

    Comment

    • TheDroz66
      Bloodstained
      • Sep 2013
      • 74

      #3
      I am measuring .67" on my 12" Faxon GB barrel, and .75" on the 16" Faxon GB Barrel.

      Comment

      • bigdaddyflo
        Bloodstained
        • Dec 2016
        • 97

        #4
        Originally posted by TheDroz66 View Post
        I am measuring .67" on my 12" Faxon GB barrel, and .75" on the 16" Faxon GB Barrel.
        Good information, but what length gas tubes are used on each barrel length? This information is very helpful. The 12" I believe is cabine length but please verify this.

        Comment

        • TheDroz66
          Bloodstained
          • Sep 2013
          • 74

          #5
          12" Faxon - carbine length tube
          16" Faxon - mid length tube
          According to the drawing provided by BFT for the original Group Buy of the 16" barrels, the gas port diameter is .78" not the .75" that I measured. My caliper could be off so the port size of the 12" barrels could be slightly larger as well. Maybe someone else can measure theirs. I don't see the port size listed anywhere on the 12" order info.

          Comment

          • Jefr00
            Unwashed
            • Aug 2016
            • 3

            #6
            Ok, why would the gas port be so much smaller on the 12", as opposed to the 16"? From what I've read, gas ports on 10.3" 5.56 barrels can be any where from .070 for a Colt Mk18 barrel to .082 for a DD MK18. I understand the DD size is so people can run any ammo, like Wolf. This is totally an aside, but what about the Grendel Wolf, does it suffer from some of the same issues as the .223 Wolf? Or, because of AA's close work with them there are no problems?

            Comment

            • BluntForceTrauma
              Administrator
              • Feb 2011
              • 3897

              #7
              Gas port on Faxon 12 = 0.073

              Gas port on Faxon 16 = 0.078

              Gas port sizes are averages, right? Ideally you'd have one type ammunition and tune the port for it. Militaries can specify this. But on the civvie side we've got tons of different bullets, powders, primers, burn rates, pressures. Our gas ports in the world of commercial ammo and civilian handloads are averages that try to work with as much as possible. I guess I just made an argument for adjustable gas blocks?
              :: 6.5 GRENDEL Deer and Targets :: 6mmARC Targets and Varmints and Deer :: 22 ARC Varmints and Targets

              :: I Drank the Water :: Revelation 21:6 ::

              Comment

              • sneaky one
                Chieftain
                • Mar 2011
                • 3077

                #8
                Meh,, kinda- if the nerd vein is there,,, and your gun- don't run. Can always change the port size with correct drill diam size,

                I'm thinking only an adjustable block is really needed outside the OEM stuff. And the suppressor items.

                Thoughts ?

                Comment

                • explorecaves
                  Warrior
                  • Sep 2014
                  • 284

                  #9
                  Originally posted by sneaky one View Post
                  Meh,, kinda- if the nerd vein is there,,, and your gun- don't run. Can always change the port size with correct drill diam size,

                  I'm thinking only an adjustable block is really needed outside the OEM stuff. And the suppressor items.

                  Thoughts ?
                  Agree. Springs/buffer weight should be all that is needed to run reliably.

                  Comment

                  Working...
                  X