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Thread: Headspace Question

  1. #1
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    Headspace Question

    Howdy,

    I've yet to build an AR but have studied the process. I think I have a grasp of headspace and the importance of it.

    That said I want to have some spare bolt parts for my DDM4 and of course a bolt.

    I assume I would check a spare bolt exactly like I was building with go-no go and maybe a field gauge. Correct?

    Also would I have a better chance of matching parts out of the box from same manufacturer of the AR? Should I get a Daniel Defense bolt and or BCG to go with my DDM4 instead of any other brand?

    May as well buy some gauges...any favorites?

    Thanks!

    W

  2. #2
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    A field gauge alone is sufficient for checking headspace. Brownells carries it.

    While not necessary, some prefer to match barrels and bolts from the same manufacturer. If both parts are within spec, it shouldn't matter.

  3. #3
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    Quote Originally Posted by Whalstib View Post
    Also would I have a better chance of matching parts out of the box from same manufacturer of the AR?
    None of the reputable manufacturer's parts would require head space checks. A headspace gauge is useful on well worn bolts/extensions. After 25 plus years on the AR platform, I may have used my headspace gauge twice.
    "What would a $2,000 Geissele Super Duty do that a $500 PSA door buster on Black Friday couldn't do?" - Stopsign32v

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    Quote Originally Posted by markm View Post
    None of the reputable manufacturer's parts would require head space checks. A headspace gauge is useful on well worn bolts/extensions. After 25 plus years on the AR platform, I may have used my headspace gauge twice.
    Agreed. A field gauge is cheap insurance when it comes to Murphy's law, though.

  5. #5
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    I just built two guns an 11.5in 5.56 and a 16in 223Wylde both with Faxon gunner barrels and used PSA/Toolcraft black nitride. I use gauges on the 11.5 but the 16 I used a BMC upper and didn't check before installing the barrel. Didn't feel like trying to heat up the upper to get the barrel out. But took both to the range and both worked flawlessly. Good parts are good parts.

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    About one in five barrel/bolt combinations in my classes and ones that cross my bench fail a go gauge.

    If you don't gauge or use the right ones, you'll never see it.

    A no go is not as important as a go and field. Those show the minimum and maximum.

  7. #7
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    Quote Originally Posted by clandestine View Post
    About one in five barrel/bolt combinations in my classes and ones that cross my bench fail a go gauge.

    If you don't gauge or use the right ones, you'll never see it.

    A no go is not as important as a go and field. Those show the minimum and maximum.
    Is disassemble of the bolt (removal of the ejector) required to properly check headspace using the go and field gages? Particularly the Brownells gages?
    You won't outvote the corruption.
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  8. #8
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    Of course the correct answer is that you should check headspace.

    On the flip side, is there evidence of catastrophic failures caused by improper AR-15 headspacing?

    If the barrel and bolt are manufactured to spec (aka quality components) the the worst case would be having both at the minimum or maximum amount of tolerance. If the headspacing is slightly short, pressure would theoretically be higher and if slightly long, brass life will suffer for reloaders.

    If headspace is drastically short, the bolt won't close on a live round, if drastically long, cases could separate (headspace would have to be ridiculously long). Case separation can absolutely cause catastrophic failures.

    I have seen plenty of pics of ARs that suffered catastrophic failures due to out of spec loading/ammo but none blamed on headspacing.

    Note that my post only applies to .556/.223 AR-15s.

    Andy

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    Its easy enough to dremel away a bit of metal from the headspace gauge, using a cutoff wheel, so the ejector does not make contact with the gauge.
    I use a live round as my "go" and a proper gauge as "no go" Of course you can get by without gauging, but why not do it and know your shit is in spec?
    If a couple/4 friends chip in $10 each, just pass it around.

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    Quote Originally Posted by prepare View Post
    Is disassemble of the bolt (removal of the ejector) required to properly check headspace using the go and field gages? Particularly the Brownells gages?
    I suggest you remove the ejector and extractor from the bolt before checking headspace on any rifle or carbine. The pressure from the ejector may have an affect on your sense of feel while applying pressure against the bolt. Removing the parts gives you an opportunity to closely inspect machined surfaces and thoroughly clean the bolt. I highly recommend thoroughly cleaning the chamber before checking headspace, so you don't get a false reading.

    It doesn't take much pressure on the bolt to get a good headspace reading. I've seen a few headspace gauges wrecked when people used them to check headspace on a fully assembled rifle.
    Last edited by T2C; 12-20-20 at 08:49.
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