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Head space gauge for M1 30 cal carbine

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  • #16
    It should be noted for the uninitiated that you check headspace on a gun that is "stripped" - ie, the main recoil spring is out of the gun, the bolt is stripped down (the firing pin and extractor/ejector are removed from the bolt).

    The barrel must be cleaned well, and then the gages inserted into the chamber. The bolt is then moved forward by hand slowly. The bolt should close on a "go" gage. It should close only partially (ie, not fully into battery) on a "no-go" gage. It should not close at all on a "field" gage.

    If it closes on a "no-go" gage, then you use the "field" gage to double-check the rifle. A rifle that can close the chamber on a "field" gage is not safe to fire, and should be taken out of service. A rifle that closes on a "no-go" gage will be hard on brass, but it shouldn't be unsafe to fire - unless something else is wrong. For a new rifle, or a rifle with a new barrel fitted, the bolt should close on only the "go" gage.

    Now, there is one more check you can do on US military surplus semi-auto rifles: You can get a "field test bolt" or a "test bolt" (they go by both names) and using a "no go" or "field" gage with a "test bolt" will tell you whether the failure to headspace is:

    - the chamber is out of dimension,
    - the bolt face has worn,
    - the bolt lugs are worn or the receiver is worn where the lugs seat.

    Those are the three things that can make a rifle fail headspace. Without a test bolt, you'll have to do some precision measurement with other instruments on the bolt and on the receiver (with the barrel pulled) and on the headspace gage in the chamber (with the barrel pulled) to discover where the cause of your headspace issue is.

    The cost of test bolts isn't cheap - they're over $200 last I saw one for sale.

    BTW, there are test bolts available for the M1 Garand, M14, 1903 Springfield as well as the M1 Carbine.

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    • #17
      Originally posted by wyop View Post
      .................

      The barrel must be cleaned well, and then the gages inserted into the chamber. The bolt is then moved forward by hand slowly. The bolt should close on a "go" gage. It should close only partially (ie, not fully into battery) on a "no-go" gage. It should not close at all on a "field" gage.

      ..........................
      And for the newbies, "closes" means lightly pressing with the tip of your finger, not seeing if you can get it to close with a rubber mallet.

      Carl - Personally I would suggest that all the information you got from those reloads, just forget about every bit of it. Buy some good quality ammo and try it again.

      If you still have questions I would suggest calling around and finding a person who has knowledge of M1 Carbines and might be willing to help or visit a local gunsmith who has the tools and knows how to check this. Do NOT make any alterations to the gun until you know exactly what the problem is and exactly what you are doing.

      http://forums.thecmp.org/forumdisplay.php?f=6

      https://www.usacarry.com/directory/c...cky-gunsmiths/

      Steve

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      • #18
        Originally posted by SteveF View Post
        And for the newbies, "closes" means lightly pressing with the tip of your finger, not seeing if you can get it to close with a rubber mallet.
        Steve is absolutely correct. This is very important. This is why you "strip" a bolt before gaging the headspace. You want to use minimal pressure to check whether a bolt will close on a headspace gage. A bolt that still has spring-loaded items (extractors, ejectors, etc) throws off your perception of how much force you need to close the bolt. You must use a minimal amount of force to close a bolt on a headspace gage in order to get an accurate reading.

        For example, when I'm checking a bolt action rifle's headspace, I strip the extractor and any ejector off the bolt, than I clean the barrel/chamber well, insert the gage, and push the bolt forward with one finger (as Steve mentions above). Then I allow the bolt handle to fall on its own - I don't push the bolt handle down. If the bolt handle will drop by its own weight, and the bolt closes completely (by seeing the bolt handle has dropped all the way), then the bolt has closed on the gage. If the bolt handle won't drop all the way, then the bolt isn't closing on the gage.

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        • #19
          Here's an article from Brownells on headspace gauges that I wrote for them several years back (when I still worked for them.) https://www.brownells.com/aspx/learn...aspx?lid=12555

          Edit: Just looked over the article on their website, and it looks like they cropped out a bunch of stuff from it. Oh, well, that happens.
          Last edited by 38_Cal; 06-15-2019, 08:00 PM.
          David Kaiser
          “You can have peace. Or you can have freedom. Don't ever count on having both at once.”
          ― Robert A. Heinlein

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          • #20
            Originally posted by wyop View Post
            Steve is absolutely correct. This is very important. This is why you "strip" a bolt before gaging the headspace. You want to use minimal pressure to check whether a bolt will close on a headspace gage. A bolt that still has spring-loaded items (extractors, ejectors, etc) throws off your perception of how much force you need to close the bolt. You must use a minimal amount of force to close a bolt on a headspace gage in order to get an accurate reading.

            For example, when I'm checking a bolt action rifle's headspace, I strip the extractor and any ejector off the bolt, than I clean the barrel/chamber well, insert the gage, and push the bolt forward with one finger (as Steve mentions above). Then I allow the bolt handle to fall on its own - I don't push the bolt handle down. If the bolt handle will drop by its own weight, and the bolt closes completely (by seeing the bolt handle has dropped all the way), then the bolt has closed on the gage. If the bolt handle won't drop all the way, then the bolt isn't closing on the gage.
            I would like to recommend "Gunsmithing made easy", by Bryce Towsley. Order it from "HamiltonBook.com, I bought my copy for $5.95. It will walk you you through a lot of projects you might be reticent yo try.

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            • #21
              Well, I've done some checking around. It appears that the M1 Carbine is a loosey Goosey gun and built to fire damn near anything you stick in it. One site said to use Scotch clear tape on the head of the round to check head space. The tape is about .0015" thick. They said that three thicknesses of the tape is equivalent to the field gauge. I used three bolts to test head space and all three bolts would close with four tapes on the head of a new military loaded round. I saw no point in going for five tapes on the round.

              After talking to a few friends that have a lot of experience with the Carbine, M1 and M2, they said if it shoots use it. None of them said to use reloads and discouraged doing so. The only issue I had was with the rounds that I suspect are reloaded and over charged. I will dispose of those and buy some factory hollow point ammo for the Carbine.

              The M1 Carbine and M1911 are the two best firearms that came from WWII. But, that is my personal opinion and need not be yours.
              It's only ink and paper

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              • #22
                Love my little M1 carbine, probably my favorite rifle

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