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Thread: Headspace check on new rifle failed GO guage. HELP!

  1. #11
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    It can be, but it's hard on tooling and you'll lose the benefit of the chrome-lined chamber.

    If it comes to the point where further reaming is warranted I'd request they replace it with a new CL barrel and verify that the chanbering job is within GO/NO GO specs.

  2. #12
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    I guess my point was that if everything is new and was assembled properly and you were to insert a FIELD gage and the bolt did not close as per the TM then I would call it good. I really don't get into the whole GO/ NO GO thing since there is no requirement for one in the TM. Just my thoughts and YMMV.

    Quote Originally Posted by erikras View Post
    Thanks for the replies!

    So correct me if I'm wrong... If my bolt does NOT close on a field gauge, but chambers a M193 round just fine, then it's safe to shoot?



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  3. #13
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    This subject of the headspace within the AR has been one of the areas that raised itself during the design of the 6.5 Grendel. Being able to address both cartridge and also chamber it was interesting to see the interaction.

    It is usual for the go gauge to use a common datum diameter and length to that shown for the chamber minimum. Lacking the mechanical leverage of a bolt action and beset with multiple contact points the ability of a chamber to digest a go gauge in an AR without slaming the action is normally an indication that the finished chamber is at least 0.001" longer than the minimum and more typically 0.002".

    It is also common to see even well made assemblies bed the high spots during the first 10 to 50 rounds and this, together with the removal of the phosphate from the lugs, will account for typically 0.002" and sometimes even 0.003" This bedding process is one of the reasons that if possible the bolt should remain with the rifle it started with.

    As a final point, consideration should be given to the fact that the barrel will elongate the chamber by around 0.001" for every 35 F deviation above the original fitting temperature.

    Given the OP description of the behaviour of the barrel with the go gauge I would assume that this barrel will settle to a very good condition.

    Turning now to ammunition, this will by definition at the maximum condition still be smaller than the minimum chamber. I have not analized the 5.56 as I do not make this caliber but I would assume that the manufactureres will run to the bottom of the tolerance band. If so I would expect to see a drop of about 0.004 below the minimum chamber.

    Returning to the OP the ammunition will be seen to fit easily and subsequent work across the rifle will settle the nominal headspace clearance to around 0.004/0.005" This can be investigated crudely by placing a circle of photocopier paper on the rear of the brass case and closing a bolt without the extractor and ejector in place. A very light resistance will be present. The go gauge will now close but adding the paper circle will prevent this.

    Bill Alexander

  4. #14
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    Bill, thanks much for your informative reply!

    Well I called Rock River Arms today. After only 5 or 10 minutes on hold I spoke with one of their techs, P.J. He was very helpful and willing to explain all I ever wanted to know about headspace and more. He said the situation I'm experiencing isn't all that uncommon. It's just that many rifles are never even checked with a GO gauge. He claims even RRA's builders do not use GO gauges when assembling rifles. They only check with a NO GO gauge. The assembled rifles are then taken to the range and test fired. If they chamber rounds, then worrying about the headspacing being too short isn't an issue. He insisted that since the lugs of my bolts rotate approx 1/3 of the way behind the barrel extension lugs, then it's only a matter of a few dozen rounds before it would close on a GO gauge. I explicitly asked if the rifle blowing up is a concern and he said no.

    Do you guys agree with this? I plan on taking it to the range this weekend and feeding it a box of Prvi .223 Match ammo.

  5. #15
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    Brownells "how to " video

    These videos are about headspacing an AR and they are easy to understand, Hope this link works..
    http://www.brownells.com/aspx/NS/Gun...p=0&t=1&i=1111

  6. #16
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    Quote Originally Posted by g1rock View Post
    These videos are about headspacing an AR and they are easy to understand, Hope this link works..
    http://www.brownells.com/aspx/NS/Gun...p=0&t=1&i=1111
    Interesting. Brownell's only says to check with a FIELD gauge. They never even mention a GO gauge.

  7. #17
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    Did you bother to read my post above? The military TECH MANUAL does not call for a GO or NO GO gage. The FIELD gage is the only one that is used. If the bolt closes on a FIELD gage then you follow the corrective action outlined.

    Remember- K.I.S.S.

    Quote Originally Posted by erikras View Post
    Interesting. Brownell's only says to check with a FIELD gauge. They never even mention a GO gauge.



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  8. #18
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    Wink Headspace

    Sometimes seeing how it's done is the best way to learn.

  9. #19
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    Quote Originally Posted by Iraqgunz View Post
    Did you bother to read my post above? The military TECH MANUAL does not call for a GO or NO GO gage. The FIELD gage is the only one that is used. If the bolt closes on a FIELD gage then you follow the corrective action outlined.

    Remember- K.I.S.S.
    Yes, I definitely read your post. And all responses to questions I post on forums for that matter. I appreciated your reply.

    However, I do keep it in the back of my mind that this IS this internet. Not all of what is posted on forums is 100% accurate. I'm by no means doubting your knowledge of the subject. But hearing it straight from the mouth of someone at RRA or seeing it done on a respected website helps reaffirm the statements I read on forums.

    Thanks to all who replied!

  10. #20
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    Alrighty then. You may want to get a copy of the military TM which is but a Google search away and you can read it for yourself.

    Quote Originally Posted by erikras View Post
    Yes, I definitely read your post. And all responses to questions I post on forums for that matter. I appreciated your reply.

    However, I do keep it in the back of my mind that this IS this internet. Not all of what is posted on forums is 100% accurate. I'm by no means doubting your knowledge of the subject. But hearing it straight from the mouth of someone at RRA or seeing it done on a respected website helps reaffirm the statements I read on forums.

    Thanks to all who replied!



    Owner/Instructor at Semper Paratus Arms

    Facebook: https://www.facebook.com/SemperParatusArms/

    Semper Paratus Arms AR15 Armorer Course http://www.semperparatusarms.com/cou...-registration/

    M4C Misc. Training and Course Announcements- http://www.m4carbine.net/forumdisplay.php?f=141

    Master Armorer/R&D at SIONICS Weapon Systems- http://sionicsweaponsystems.com

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