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  • wildrider666

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    POST #19 Figure is the "Cartridge". Go to Link, it's SAAMI PDF auto download. Open it, Your's is at page 98. Top figure is cartridge (ignore), bottom figure is "CHAMBER" on bottom Left is the Key. "X" inside "○" denotes "HEADSPACE" measurements between corresponding lines with arrow tips. From bottom/base of the gauge to the First sharp edge then mid shoulder angle. "Go" number you provided (on gauge) 1.079 is .0001 Larger than SAAMI listed Minimum of 1.0789. Its a miniscule difference but it's there none the less and more than likely the gauge and or number is just "Rounded Up". Gauge should still be measured to verify its true size verse above numbers and tried again "with Marking" with the stripped bolt face and clean surfaces.

    https://saami.org/technical-informa...FjADegQIBhAB&usg=AOvVaw2Jzcx_d_joThicyEFxSQdM
     
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    mtbbrewer74

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    I saw this post on a different site, and was wondering what ya'll thought about it. It is not the same brand barrel I have, but it is the same problem.


    "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."

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    FrommerStop

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    Thanks for that information. So they are using the cartridge to determine that minimum dimensions are good and use a no go gauge to determine that the chamber is not unsafe. No idea, but I guess it is likely done by many in the gun manufacturing industry.
    The bolt 'wearing in' I wonder about. The AR system using a multi-lug bolt lock up and I can easily see one lug lockup or more on the bolt being being out of spec. That they wear in or deform enough for headspace to wear in, well I would have to ask others about that.

    I would hope that the more expensive AR's have better QC.
     

    mtbbrewer74

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    I contacted my barrel manufacturer and they told me that their QC department checks headspace, and test fires. They told me to check again after I get the Ejector, and Extractor out. After that let them know if there is a problem.

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    reel_crazy

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    The average hobbyist is quite limited to what he/she can measure with any run of the mill micrometer. Below is a Saami spec chamber drawing.
    1.1021 is the max length for the shoulder run out for a minimum chamber. To determine the other measurements requires equipment that is beyond the means of most people. I know of one gunsmith in town that likely has equipment that can do it. It is used for precisely measuring parts so that he can precisely replicate them. you must be able to measure angled surfaces.
    I do not believe that head space gauge will measure the throat or length of the neck. I believe it only determines if the shoulder of the case is correct.
    View attachment 75084

    i do have a decent digital height gauge and surface plate which could determine the dimensions ... at least within half a thou or so... i currently do not own any certified guage blocks that would be needed to confirm this.. but anyone on here is welcome to it if needed ... rich
     

    mtbbrewer74

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    I contacted my barrel manufacturer and they told me that their QC department checks headspace, and test fires. They told me to check again after I get the Ejector, and Extractor out. After that let them know if there is a problem.

    Sent from my SM-G955U using Tapatalk
    I am supposed to have the tool Friday that helps remove the Ejector. If it goes smooth after that cool, but if not I will get back with the manufacturer.

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    wildrider666

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    I saw this post on a different site, and was wondering what ya'll thought about it. It is not the same brand barrel I have, but it is the same problem.


    "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."
    Sent from my SM-G955U using Tapatalk

    That's an interesting Post if info is truly from the Source:

    It can be interpeted as "The upper is like others from RR, out of "SAAMI Spec" but "good to go. Q: Was this barrel out of spec by .0001 or .030? How does the Rep know the measurement in order to give that advice? This sounds like a variation of the Mfr blow off that you need to break-in a product before it will function correctly. Products should be in Spec and functional upon arrival, thats what we pay for.

    OR interpeted as The problem is not uncommon, we don't use proper "Go" Headspace gauge check so a lot of Barrels/Ext may not pass. We test fire with ammo instead, even though cartridges are manufacture to a SAAMI spec which are by design "smaller" in order to fit (Min/Max) chamber size variations from manufactures. (Really?) This conflicts with an article titled" A inside look at Rock River Arms AR-15 Factory, July 17, 2009 in Field & Stream (it's online but Link won't paste). This article shows pic of and Go/No Go gauges and references their use. It does show a van at the test range with complete firearms and uppers and states RRA test fires all firearms. Note: info is 10 years old.

    Cutting and measuring tools wear with use and dimensions "shrink". Good QC checks tooling limits too. "A Few dozen rounds" will fix the "Headspace"? So, its going to wear down the bolt face or chamber shoulder that fast? If we follow this Logic that 36+- rounds will bring it (how much out of Spec) into Spec, will it continue to wear at the same rate?

    Just wait until you get good numbers. You might not need "options".
     
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    While reading this whole thread, I can't stop thinking, "this discussion is regarding a firearm designed with a forward assist button". I'm with Frank T. on this one, and I'll volunteer to be "Mikey", as long as someone else provides the ammo.
     

    wildrider666

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    While reading this whole thread, I can't stop thinking, "this discussion is regarding a firearm designed with a forward assist button". I'm with Frank T. on this one, and I'll volunteer to be "Mikey", the ammo. as long as someone else provides

    We can view it a technical issue or choose not to. The "Gauges" are used specifically with light finger presure. I don't think this is the case at hand but if it requires the use of a Fwd Assist to seat a clean spec cartridge into a clean spec chamber something is wrong. IMHO

    if we connect to OPs' prior thread, he inquired about the need for chamber gauges for his build with a factory assembled Upper. He was told Yes, No, you could blow up, ect. He buys Gauges to be Safe and now there may or may not be a problem since true measurements are still pending. I'm pretty sure one of our Mods did a build and has a very tight chamber. His fix was to reload ammo to fit that chamber IIRC.
     

    FrommerStop

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    Just a reminder the parts that will determine headspace on an AR:
    Barrel chamber
    Barrel Extension
    Bolt
    I am not sure what the average person can do with these parts except change them out with the bolt being the easier to deal with to see if incorrect headspace needs to be corrected. I am looking this up for my own education.
    Picture of barrel with barrel extension installed and then the barrel extension by itself. This is where the bolt locks into. The distance from the face of the bolt to the shoulder on the chamber determines the headspace. If the gas port is already drilled the screwed in position of the chamber extension can not be changed.
    i imagine a gunsmith with a lot of different bolts could adjust headspace by finding one that had the right measurements.
    25guszsAR Barrel extension.jpg
    AR-10-BARREL-EXTENSION.jpg
     

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    mtbbrewer74

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    While reading this whole thread, I can't stop thinking, "this discussion is regarding a firearm designed with a forward assist button". I'm with Frank T. on this one, and I'll volunteer to be "Mikey", as long as someone else provides the ammo.
    I am not sure what your thinking is regarding a firearm designed with a forward assist button? Please educate me.

    Also the " Mikey" reference went over my head.

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    FrommerStop

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    I am not sure what your thinking is regarding a firearm designed with a forward assist button? Please educate me.

    Also the " Mikey" reference went over my head.

    Sent from my SM-G955U using Tapatalk

    It is a push operated control on the end of the upper receiver that will apply force to the bolt carrier pushing it forward and will cam the bolt forward and cause to turn in lock in the face of moderate resistance. It was not part of the original design of the original AR design.
    I would rather eject a round that will not chamber rather than try to force the bolt to close. It is possible to end up with a round jammed tightly in the chamber with bolt not closed and no easy way to eject it.
    This what I would use it for
    the forward assist can prove useful is when performing a stealth chamber check. Rather than letting the bolt go forward under full spring tension after verifying a round is in the chamber, the bolt can be let forward gently and then the forward assist can be used to fully close the bolt. Doing so will produce a very distinct "click" rather than the loud sound of the bolt slamming forward.

    The original use was partway through the firearm's use in the Vietnam War. Before the forward assist, the M16 was often carried "Locked and Loaded"—that is, cocked with a round in the chamber, and with the safety on—because the noise made by a platoon of some 30 men pulling back and releasing the bolt handle would alert the enemy of their location. The assist allowed soldiers to carry a firearm without a round in the chamber until necessary.
     
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    mtbbrewer74

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    It is a push operated control on the end of the upper receiver that will apply force to the bolt carrier pushing it forward and will cam the bolt forward and cause to turn in lock in the face of moderate resistance. It was not part of the original design of the original AR design.
    I would rather eject a round that will not chamber rather than try to force the bolt to close. It is possible to end up with a round jammed tightly in the chamber with bolt not closed and no easy way to eject it.
    This what I would use it for
    I know what the forward assist does, but I just don't understand how the reference had anything to do with checking headspace.

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