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

  1. #1
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    Question Headspace check on new rifle failed GO guage. HELP!

    I did a search here and couldn't find quite the answer I was looking for. Maybe I missed it.

    I just finished assembling my new upper using the following parts:

    Sabre Defence 1:7 14.5in 5.56 chrome lined mid-length barrel
    Rock River Arms BCG
    Yankee Hill Machine ("Keyhole" marked) stripped upper
    Clymer 5.56 GO and NO-GO gauges from Brownell's.

    I assembled everything using the proper tools and a Snap-on torque wrench that was recently re-certified. Torqued the barrel nut to 35ft-lbs then tightened it until the next hole aligned with the gas tube.

    I thoroughly cleaned the chamber of the new barrel and inserted the NO-GO gauge. It didn't even come close to closing. Good. I moved onto the GO gauge. The bolt began to slightly rotate into the locked position behind the locking lugs of the barrel extension. However, it would not go into full battery. I had another brand new RRA BCM laying around so I tried it. Same exact problem. I then tried chambering some M193 and various .223 Hornady and Prvi rounds. They all chambered with no more effort required than closing the bolt on an empty chamber. Next I tried a slightly used (less than 100rds) RRA BCG that I had out of another fairly new rifle. This bolt closed on the GO guage with only moderate force. (i.e. I was able to push it closed wit the palm of my hand.)

    It's important to note that the bolts were NOT stripped during these test. Is that my problem? Will stripping the bolt give me the required added clearance?

    Is there a known issue between RRA bolts and Sabre barrels?

    Being that the bolt "almost" locks, would it be safe to shoot low powered .223 ammo to "break in" the new bolt and chamber?

    Thanks for the help guys. This is my first time assembling an upper. I'm an anal retentive Mechanical Engineer so I like mechanical things to work perfectly!

  2. #2
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    Headspace Gauge

    With brand-new bolts check to make sure the extractor is going over the rim of the headspace gage, otherwise the bolt carrier group may not be going all the way forward (as you noticed, may not be rotating and locking into the barrel extension).

    DO NOT drop the bolt carrier group onto the gage by hitting the bolt stop and letting that huge mass bash the gage into the chamber.

  3. #3
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    Quote Originally Posted by sinister View Post
    With brand-new bolts check to make sure the extractor is going over the rim of the headspace gage, otherwise the bolt carrier group may not be going all the way forward (as you noticed, may not be rotating and locking into the barrel extension).

    DO NOT drop the bolt carrier group onto the gage by hitting the bolt stop and letting that huge mass bash the gage into the chamber.
    The extractor was going over the headspace gauge. For that matter, it was extracting it. While doing these tests the upper and lower were not mated so I was not dropping the bolt onto the gauge.

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    I always remove the extractor when checking headspace.Just makes it easier for me.
    As far as not closing on a go...both of my new Armalite M15A4 20" uppers I bought last fall were tight on a go gauge.I installed LMT BCG's and they headspaced perfectly on a go and would not close on a Brownells Colt 5.56 Field.So I ran with it.
    Checking the depth of the bolts showed the Armalite bolts had .002" less recess to the bolt face than the LMT.
    Same with my older 2000 model Armalite M15A2.It will not close on a go gauge and has an excessively tight leade to boot.It shoots .223 Rem ammo perfectly,but will not chamber 5.56 NATO at all.Forces the ogive of the bullet into the leade which is nota good thing.
    So I would try another/better bolt and see what you get.
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    My recommendation would be to get a FIELD gage since there is no requirement for a GO or NO GO in the TM. If it passes then you are good to go. Bushmaster sells a true 5.56 FIELD gage for about 25.00 or so. Also, Bill Ricca had genuine USGI gages for about the same price. I bought 3 of them and use one at my shop all the time. I also use the FIELD gage on my personal AR's as well.



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    Quote Originally Posted by Iraqgunz View Post
    My recommendation would be to get a FIELD gage since there is no requirement for a GO or NO GO in the TM. If it passes then you are good to go. Bushmaster sells a true 5.56 FIELD gage for about 25.00 or so. Also, Bill Ricca had genuine USGI gages for about the same price. I bought 3 of them and use one at my shop all the time. I also use the FIELD gage on my personal AR's as well.
    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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    Can't answer your last question but I will say this: Do Not chamber a cartridge and insert BCG into upper that is not fully mated to a lower! Let's say the assembly slips out of your hand, next thing you know have a .224 hole in your foot and the BCG flew out the upper and hit you in the twig and berries. I know you probably thing you are safe enough to do this, but it's this type of complacency that hurts people. Use the gauges, save the ammo for the range.

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    Quote Originally Posted by PlatoCATM View Post
    Can't answer your last question but I will say this: Do Not chamber a cartridge and insert BCG into upper that is not fully mated to a lower! Let's say the assembly slips out of your hand, next thing you know have a .224 hole in your foot and the BCG flew out the upper and hit you in the twig and berries. I know you probably thing you are safe enough to do this, but it's this type of complacency that hurts people. Use the gauges, save the ammo for the range.
    I honestly do appreciate the warning. I guess it's something I never really thought about. Luckily, I happened to have the upper held in a vise while working on it. (Rubber jaw pads holding the free float tube.) Normally, I don't have it secured like that. 95% of the time while working on guns, it's just sitting on the bench in front of me.

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    Cartridge/ammunition specs will be tighter than chamber specs.

    A chamber reamed to "GO" dimensions is supposed to accept any "in spec" cartridge. That means the "in spec" cartridge has to be shorter dimensionally than the chamber spec.

    The "No Go" covers the allowable variance in the chambering operation.

    Purchasing a FIELD guage when your chamber won't accept a GO guage won't address your situation.

    I'd recommend you remove the ejector and test accordingly. If still snug, send it back. It would need further reaming.

  10. #10
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    Thanks again for all the replies an advice.

    Can a chrome lined barrel be reamed?

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