Headspacing: Is GO gauge supposed to equate to never-fired brass?

Discussion in 'Gunsmithing' started by Max Heat, Mar 22, 2012.

  1. Max Heat

    Max Heat Well-Known Member

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    I'm looking for the poor man's way to check for excessive headspace in a center-fire rifle. Obviously, the bolt should close without any resistance on brass that has never been fired. My question basically is: How thick of a shim can be placed between the bolt face and the fresh (I would try 5 to 10 of them, to establish an average) brass, before the bolt gets hard to close, or won't close?

    If I punch out a round piece of aluminum from a can that is slightly smaller in diameter than the rear of the shell, place it behind it, and the bolt will close on it with only slightly more pressure, is that too much headspace? The aluminum is .004" (4 mils) thick. The gun (Savage 7mm rem mag) HAS had some pretty hot loads though it, one in particular that was way too hot, and roughly 500 rounds total through it.
     
  2. dirtball

    dirtball Well-Known Member

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    NEVER use a brass case to check headspace. New brass is undersized so it should fit in any chamber, that undersizing varies from lot to lot from the same manufacturer and varies a LOT between manufacturers.
    Take the gun to a gunsmith and have it checked if you are concerned, or buy a GO gage from Midway or some one else, they are about $28.00.
    The GO gage can be used with a piece of scotch tape as a NO GO gage, the scotch tape adds about .0025 and the bolt should NOT close.

    Dave


    Search results for: go gage
     

  3. Max Heat

    Max Heat Well-Known Member

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    OK, new brass is undersized then. I don't want to spend on a rem mag gauge at this point because I plan on re-barreling soon anyways, and also chambering-up to RUM, while I'm at it. So I don't see the sense in also spending on a gauge for a barrel/chamber that I will be ditching soon. I was just curious if the over-charged load took it out of spec. On that shot, the chrony showed 3875fps on a Nosler 120 BT, and the bolt was definitely tight coming up (powder was RL19). Assuming a linear relationship between charge weight and energy produced in the fired round, my estimate on what the charge weight had to be in that round puts it at about 83 grains, a 9.5 grain or a 13% over-charge! I'm not really sure how it happened.

    I guess it really doesn't matter if that one took the rifle's headspace out of spec, since the barrel is slated to be swapped out to the RUM barrel in about a month or so, anyways. I'll just play it safe and not fire it any more until then. But what REALLY scares me now, is that the RUM setup that I will be switching to may not be so forgiving of a mistake of that magnitude.
     
  4. FEENIX

    FEENIX Well-Known Member

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    +1. Improper headspace could result in destruction of the rifle, injury, or even death. Don't take chances! Always check the headspace properly and with the right tools before firing.

    Any other concoction is at your own risk. IMHO, there is no compromise when it comes to safety.

    Good luck and happy safe hunting/shooting.
     
  5. J E Custom

    J E Custom Well-Known Member

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    A head space gauge is based on SAAMI specks and all ammo is sized smaller in order to fit
    any chamber. The use of ammo to head space a chamber is not recomended because is is
    difficult to know what there size is compared to SAMMI is There can be .003 to .005 Thousandths
    difference between brands.

    It is common however to check factory ammo for for fit after the chamber has been head spaced.

    If the ammo is new .004 worth of shims should be tight/snug but if it is fired in that chamber it
    should not go at all. (Note: if you force the bolt closed on a fired case with a shim behind it of
    any thickness it will set the shoulder back on the case and will not tell you anything) That
    is why you must use a head space gauge that will not compress.

    J E CUSTOM
     
  6. Max Heat

    Max Heat Well-Known Member

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    Ok, I forgot to mention, that right now I don't even posses any un-fired brass. It WAS fired (maybe 4-5 times) Winchester brass that I could close the bolt on with minimal resistance with the 4 mil aluminum shim behind the cartridge.

    Here is the other thing that concerns me: On several of the shells that were fired in the rifle after the over-charged shot, and then were reloaded, the primers fell out, indicating that the primer pockets are streched! Is this an issue with the brass itself, or is it a more serious issue? I am NOT firing the gun right now, and don't plan on firing it again until AFTER my new heavy stainless 7RUM barrel goes in.

    Who makes or sells a GO gauge for 7RUM? I'm having trouble finding one.
     
  7. FEENIX

    FEENIX Well-Known Member

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  8. Max Heat

    Max Heat Well-Known Member

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    I have found out that any ultra mag gauge will will work for any OTHER ultra mag caliber, WITH THE EXCEPTION OF THE 338RUM, which would need it's own SPECIFIC gauge. I'll get a 300RUM gauge, but what is the best brand? I've found that Forster, Clymer, Manson, and Ackley make them. But I've also heard that there are variances between them, within the SAAMI spec. I want to use the one that is the tightest (shortest).
     
  9. J E Custom

    J E Custom Well-Known Member

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    I use Manson,PT&G and Clymer and have found them to be very accurate to SAAMI spec.

    I normally use the same brand head space gauge as the reamer I use for the chamber.
    there should be no difference , but it just makes sense to me that they both be cut by the
    same company.

    Note: The head space gauge will not be tight on the sides of the chamber. It is used only to
    set the chamber length (Head space) of the chamber. Also if you notice, SAMMI has two sets
    of dimensions for each cartrige. One is for the chamber and the other is for the cartrige
    manufacture.

    J E CUSTOM
     
  10. shortgrass

    shortgrass Well-Known Member

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    Man, SAAMI spec is SAAMI spec, the standards of the shooting sports industry. These gauges each have a serial number on them. They are made to industry specifications (SAAMI, Sporting Arms and Ammunition Manufactures' Intitute). Call any of the makers and ask this same question and I'll be able to hear the laughter from here! If you are worried about it, take the rifle to someone reliable who understands gauging and have them check it for you. www.saami.org
     
  11. shortgrass

    shortgrass Well-Known Member

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    By the way, there are two gauges needed to check your factory rifle, a GO and a NO-GO. In your case of "over pressure" I'd be usin' the NO-GO first. "Over pressured" components deserve an inspection by someone familiar with what they are looking for and they should be Magna Fluxed. You could be dealing with a potential "catastrophic failure", not just a headspace issue.
     
  12. FEENIX

    FEENIX Well-Known Member

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    I think there were plenty of warnings given ... lightbulblightbulblightbulb
     
  13. Bughole

    Bughole Well-Known Member

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    The pressure relationship is not linear past the point of safe charge weights.. It's exponential. You can't simply interpolate the velocity and the charge weight or over charge etc. and draw any conclusions from the rationale you presented. Check and recheck your practices for loading, sounds like you got lucky! You might not be so lucky the next time.