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  1. #1
    shepherm is offline Plastic
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    Default AR15 gas port hole location

    Ok I am building a 6x45 and plan on using the rifle gas tube but how do I know where to drill the hole. I have the barrel on the lathe and turning it down but need to know how far the gas block and port is from the chamber end.
    Thanks
    Mark

  2. #2
    biometrics's Avatar
    biometrics is offline Cast Iron
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    Go to Biggerhammer.net. There are AR15 blueprints there. You should be able to get the info from the blueprints.

  3. #3
    Dtech is offline Aluminum
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    On barrels with the rifle-length gas-system, I make the shoulder for the gas-block 12.125" from the shoulder that the barrel-extension screws up to.

    Hope that is what you were looking for.

  4. #4
    RWO
    RWO is offline Cast Iron
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    The NRA AR-15 book shows the port to be 12.420" forward of the barrel shoulder that stops the barrel extension.

    RWO

  5. #5
    MilGunsmith's Avatar
    MilGunsmith is online now Hot Rolled
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    Try to center the gas port hole in a groove. You will have better accuracy and less problems with fouling in the port.

  6. #6
    shepherm is offline Plastic
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    Ok great thanks for the help. I got the barrel turned down to 1in and threaded for the extension. Now I am going to finish turning it to the .937 for the gas block and then order the reamer.

  7. #7
    Dtech is offline Aluminum
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    I like going about it the other way around. If you profile and thread the barrel first, you are on the hook to make the chamber perfect the first time. I rough the chamber, then finish it. After close inspection, I cut the blank to about 1/4" longer than the desired barrel length. Then I put the barrel between centers and thread it. After I install the barrel-extension, I proof-test the barrel with one shot. You can inspect the brass carefully for any problems in the chamber, and borescope the throat and bore for any problems as well.

    If it passes those "tests" then I profile the barrel, and eventually drill and ream the gas-port. Once you profile it, or drill the gas-port, you are pretty well stuck with what you have. If you end up with a problem in the chamber, and catch it prior to profiling, you can cut the shank off and start over.

    With all due respect to MilGunsmith, I have never made any attempt to time the gas-port into a groove. Before I started chambering my own barrels, I took the advise of one of the most respected AR smiths in the country. He doesn't "time" the gas-port to the groove, so I never did either. I drill and ream the port when everything else is done, and have never had any adverse results from where the port ends up. Take care in drilling, reaming and removing any small burr that may remain, and you will be in fine shape.

  8. #8
    shepherm is offline Plastic
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    Well now you tell me!! Just joking. I did profile it to 1" and then to .938 for the gas block. I guess if I mess up I can still set it back and use .750 gas block. This is my first time so I am learning the hard way, but so far so good. I have a jet 13x40 lathe and so far it is doing good job. Thanks I again for all the help.

  9. #9
    Dtech is offline Aluminum
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    You didn't "mess up". I was only telling you how I do it, and why. I spent most of my life in medical and industrial electronics. Many operations I would have to preform could cause tens of thousands of dollars worth of damage if done incorrectly. It just changes the way you think, and proceed through a procedure. Most of the time it isn't necessary, but once in a while it will save you a pile of work, or a scrap barrel.

    Make sure you have any small burrs taken care of before you fire it. There are many ways to do it, but if you drill the port one number size smaller than the desired port, then ream it to size, any burr left will be very small. I use a VERY tight fitting bore brush to break off any remaining burr.

  10. #10
    madokie is offline Aluminum
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    Thumbs up AR gas port location

    it depends on barrel lenght,16" have it 4-6" from muzzle,as do 20".the M4 carbines the military has are problamatic,as to reliability,thier GP location is 2-3" from muzzle,its too close,as gas preasure dosent have enough time to properly cycle weapon.M1 rifle has this prob,and ammo must be precisely loaded f proper funtioning,not just any 30-06 ammo will work in m1 rifle.keep your GP location at least 6" from muzzle.

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