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Thread: colt 6933 vs cut down colt 6720

  1. #31
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    Quote Originally Posted by MK18Pilot View Post
    I wouldn't recommend cutting a 6720 barrel to any length. The 6520/6720 barrel is flared at the end to support the crush washer. The shoulder created during threading will not be sufficient to support the crush washer properly.
    If you understand this and select a muzzle device that will index on the muzzle not the shoulder then it's not a problem.

    Selecting a barrel that is larger at the muzzle end but the same under the handguards to reduce POI shift seems odd to me.

    The number of people who shoot suppressed only rifles is very small, that's why there are no rifles made that way. Rifles with suppressed only gas ports should not be considered reliable without the silencer.

  2. #32
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    Quote Originally Posted by Todd.K View Post
    If you understand this and select a muzzle device that will index on the muzzle not the shoulder then it's not a problem.
    Is there a suppressor manufacturer that advocates this method of indexing for a muzzle device? What cutting tool would you use in the counterbore to ensure that the bottom was square to the bore of the barrel?

  3. #33
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    Quote Originally Posted by turdbocharged View Post
    Please correct me if I am mistaken, however,

    I thought it was a best practice to run a thicker barrel profile for a supressor, since you have so much dead weight out front that can cause more POI shift on the thinner profiles.
    Which only matters if you are going to be taking the can on and off. With a fulltime can there is no shift.

    I'm working on a carbine now with a 10.3" Daniel Defense 0.625" dia. barrel. If it works out I'll likely be putting together an identical upper for fulltime suppressor use, and won't give POI shift a second thought.

  4. #34
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    AAC does, the length of threads needed to index on the muzzle is in their thread specs. The bottom of the mount is as square to the bore as the threads and back if they are cut in the same op.

  5. #35
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    I guess I'd have to see one cut in half to fully grasp how it's finished. It would seem that a boring bar would have to be used to relief cut the corners of the counterbore and in my mind it wouldn't leave enough purchase between the face of the muzzle and the suppressor mount to rely on square fit. AAC gets the benefit of the doubt though.

  6. #36
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    It has internal thread relief and the face cut square with a boring bar I assume. It's not like an A2 with the angle of the drill at the bottom.

  7. #37
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    Quote Originally Posted by markm View Post
    I disagree. I mean.... I run my can on a Bushmaster for Pete's sake. That is a big port. Just bump up the buffer to H2 or H3.
    Have you run it without lubrication, for extended periods of time?

    I have, both suppressed, and unsuppressed. This port size works well for me with 5.56mm pressure ammo.

    Quote Originally Posted by scottryan View Post
    If he cuts the barrel, the gas port is no longer spec for that length of barrel.
    There is no gas port specification for suppressor use. For unsuppressed use though, I gotcha. But there are middle-grounds. Like for a suppressed gun where the suppressor will NEVER come off it'd be something like .048'' or .050'' or something super tiny. The gun wouldn't even cycle unsuppressed. .056/.060'' or more, will cycle unsuppressed, and will be reliable.

    Quote Originally Posted by Todd.K View Post
    Rifles with suppressed only gas ports should not be considered reliable without the silencer.
    Agreed. That's why mine is slightly bigger. I subscribed to Grant's train of thought, and built my guns based on his theories, and findings. After he did them first. I trusted his decisions, and the overall builds have worked for me.

    VLTOR A5 will make the bolt lock back unsuppressed. Just a footnote, btw.

    Quote Originally Posted by scottryan View Post
    The gas port should be sized for mil spec ammo unsuppressed. That way it insures reliable functioning when the gun is dirty.
    That's if the gun will be shot primarily unsuppressed. Mine is ported for (close to) milspec ammo suppressed. Actually it's ported slightly larger than that.

    Hope the replies make sense. I was in a hurry.
    Last edited by Magic_Salad0892; 08-31-11 at 05:25.
    We miss you, AC.
    We miss you, ToddG.

  8. #38
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    Was it established that the 6720 and 6933 have different size gas ports, and if so do we know the sizes, or are we just assuming they are different based on the different barrel lengths.

  9. #39
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    It's my understanding that 6720 has .062'', and 6933 has .071''. (or .090'' that I read from a Robb Jenson post.)
    We miss you, AC.
    We miss you, ToddG.

  10. #40
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    Quote Originally Posted by MK18Pilot View Post
    Is there a suppressor manufacturer that advocates this method of indexing for a muzzle device? What cutting tool would you use in the counterbore to ensure that the bottom was square to the bore of the barrel?

    The AAC miter mount indexes off the muzzle face.
    "Not every thing on Earth requires an aftermarket upgrade." demigod/markm

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