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Thread: Headspace Gauges

  1. #1
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    Headspace Gauges

    I have a few projects coming up that will require me to remove and install barrels so I have been looking up information on head space gauges. I think I understand most of it, but I still had a few questions. Please correct me if anything I say below is not correct:

    Are No-Go Gauges the same as field gauges?

    Are No-Go Gauges the most important?
    It seems like most people who post say that excessive head space is the most dangerous. What is the point of the go gauge? Should I get them both?

    What is the proper way to read the Gauges?
    From what I have read a no-go gauge should prevent the bolt from locking up, but a go gauge should allow it to lock up.

    Do I need a 5.56-marked gauge?
    Several people on different threads have recomended this gauge:
    http://www.brownells.com/gunsmith-to...-prod6646.aspx
    It says 5.56 in the description, but it says .223 on the side. Should I be worried about it not being marked 5.56? This does not say it is a "go" gauge so I assume it is a field gauge.

    Do I need to check headspace if I take apart a factory rifle?
    One of my "projects" is going to be taking the barrel nut off my current gun to install a FF rail. The same barrel and bolt will go back together. Should I worry about headspace in this case?

    Are there any headspace gauges that do not require removal of the extractor?
    It seems like most people say this is required, but I was thinking maybe there was one somewhere that would not require me to remove this.

  2. #2
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    Removing and replacing barrels doesn't impact headspace. There's nothing you can do to alter headspace.

    Thus hence in the situmahwayshun you're in, I wouldn't bother with one.
    "You people have too much time on your hands." - scottryan

  3. #3
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    There have been several good threads on headpspace gauges and how to use them. You should be able to find them by using the orange search button. Iraqgunz is very knowledgeable and has posted good info on the subject
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  4. #4
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    Quote Originally Posted by MistWolf View Post
    There have been several good threads on headpspace gauges and how to use them. You should be able to find them by using the orange search button. Iraqgunz is very knowledgeable and has posted good info on the subject
    I know better than to post without searching. There are 1220 results for "headspace gauge" in approximately 100 threads. I read many of them and skimmed many others, but I still do not know everything I feel like I need to.

    A lot of the information is contradictory. For example:
    In this thread:
    https://www.m4carbine.net/showthread.php?p=1542256
    Somebody says you need both the go and nogo gauges
    In this thread:
    https://www.m4carbine.net/archive/in...p/t-60269.html
    Rob Jenson (who I would consider an expert so I am inclined to listen to him) says you only need a field gauge unless you are an barrel maker.

    I found (on wikipedia after I posted here) that the field gauge is slightly larger than a no-go gauge.

    This is a safety issue so I am trying to make sure I understand it. At the moment I plan on just buying a 5.56mm (actually marked "5.56" on the side) Field Gauge and using that. I understand the chamber dimensions, but I do not understand why there is a need for a Field gauge and a nogo (wikipedia says the nogo might fit on a "stretched" bolt, but why would you not just only use a field gauge then). I also do not know why too little headspace (I assume the bolt not closing on a go gauge tells you this) is not a concern. I guess I will just do that, but I was hoping to understand more about it than a simple "use this gauge".

    MarkM, thanks for the answer about the factory gun. I will be installing my new handgaurd before I do my other "project" (I plan on assembling my own gun from random parts I have been gathering for a while...That is mostly when I will need the gauge it sounds like)

  5. #5
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    A quick overview, and i understand the overload of search results.

    A Field gage is of no use to you. It is the maximum allowed headspace, per mil-spec. A rifle that won't gobble up a field gage is considered good to go in a military context. If you have a rifle that is over No-go, but won;'t take a Field, it is safe, but your brass will have a sorry and short life.

    If the factory set headspace properly, then taking the barrel off while replacing a FF handguard won't change that.

    If you are installing bolts and barrels as sets, but they didn't leave the factory together, a go and no-go would be nice.

    I've always taken the extractor and ejector off, so I get a feel for the fit unhindered by the mechanical distractions of spring pressure, etc. yes, you can buy gages machined to clear the ejector, but I've never bothered.

    And the go and no-go come in sets. Don't mix brands. The makers machine them to specific dimensions (and the military ones also differ slightly) and if you mix you could be not getting the info you think you are getting.

  6. #6
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    When I was in Iraq a certain large company on a DOS contract purchased commercial .223 Go and No Go gages. When they used them it resulted in several false readings. These M4's had actually seen very little actual live fire use.

    I only use the 5.56 Field Gage and only use know quality parts. This seems to have worked pretty good for me in the hundreds of AR's that I have put together over the years.



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  7. #7
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    Quote Originally Posted by Iraqgunz View Post
    When I was in Iraq a certain large company on a DOS contract purchased commercial .223 Go and No Go gages. When they used them it resulted in several false readings. These M4's had actually seen very little actual live fire use.

    I only use the 5.56 Field Gage and only use know quality parts. This seems to have worked pretty good for me in the hundreds of AR's that I have put together over the years.
    Where could someone buy a 5.56 Field Gage? Preferably one with the narrow base requiring less bolt dissasembly. I have looked in the past but must not have the magic search terms because I haven't been able to find one for sale online.

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    Bill Ricca took care of me. http://www.billricca.com/collectors_corner.htm

    The guage is half way down the page.

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    Again, a field gage is fine in a military context/use. They are not the least bit concerned about the reloadability of fired brass.

    If you plan to reload, you may want to know something more than "won't take a field gage" as far as headspace is concerned.

    Also, if your bolts(s) and barrel(s) come from different sources, you may want to know more.

  10. #10
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    Quote Originally Posted by patrick sweeney View Post
    Again, a field gage is fine in a military context/use. They are not the least bit concerned about the reloadability of fired brass.

    If you plan to reload, you may want to know something more than "won't take a field gage" as far as headspace is concerned.

    Also, if your bolts(s) and barrel(s) come from different sources, you may want to know more.
    Patrick, as always, sound advice. Your work is very much appreciated. Honest, down to earth writing !!

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