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Thread: 8mm Headspace

  1. #11
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    Default Re: 8mm Headspace

    What exactly is a field gauge measuring? From what I gather, Go is min SAAAMI and Field is max SAAMI whereas no go is just some number setup by who made the gauges?

    Just curious
    Una Salus Victis Nullam Sperare Salutem

  2. #12
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    Default Re: 8mm Headspace

    For most cartridges there is a 0.010 inch difference between the minimum and maximum chamber specs.

    Go is cut to the minimum chamber specs.

    No-go is generally cut 0.003 larger than minimum. This is what gunsmiths generally use to chamber a new barrel and not have it too "tight" for various brands commercial ammo.

    Field is supposed to be cut to the max chamber spec But are usually cut 0.008- 0.009 inch longer for liability reasons.


    To further confuse things, headspace is a close but inexact measurement based on an arbitrary datum line on the shoulder of the case. The problem is there is a difference of where they measure this datum line between the modern SAAMI and the original Military chamberings. Also there are minor differences between gauge manufacturers. It is well known that the Clymer 30-06 gauges are cut closer to the original 30-06 specs. Foresters are cut to SAAMI. There are cases where a chamber will close on a Forster field but be OK with a Clymer gauge

  3. #13
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    Default Re: 8mm Headspace

    My field gauge came yesterday guys, aaaaaaaand I bought the wrong one. I bought a 7x57, not 8.

    Pretty sure this wont work because the length? But if you experts have any opinions let me know..


  4. #14
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    Default Re: 8mm Headspace

    Looking at the chamber specs of both it will NOT work. The 2 cases differ my more than just changing the neck diameter

  5. #15
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    Default Re: 8mm Headspace

    I appreciate you guys so much you're basically saving me some cash and preventing me from blowing my face apart!

    You're good people! Anybody local that sells a good headspace gauge? I don't mind buying online but I'd rather see it and be able to hold it in my hand before I buy, it's just the way I was brought up..

  6. #16
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    Default Re: 8mm Headspace

    Lucky day, my box of 8mm Mauser came today so I did the old tape trick. Yeah I know its frowned upon but screw it..

    Measured the full round at 75.2mm took 4 layers of Scotch tape, bulked it up to 80.8(+00.1 MAYBE, cheap caliper)
    Stripped the bolt fully but the round in the chamber and this was the outcome...



    Closed to the first point resistance, but again like the NO GO I bought, its not fully closed. I'm no gunsmith but this looks to me like it passes the rigged field gauge test?

  7. #17
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    Default Re: 8mm Headspace

    Your 4 layers of scotch tape are probably around .007". That's what my four layers measured. If the bolt locks completely with no interference on a cartridge out of the box, and exhibits the bind you have depicted on the taped head of that same cartridge, it appears it is safe to fire that cartridge. Measuring the thickness of the tape before application gives a little more knowledge of where it is.

    If you do a lot of measuring of factory cartridges, you'll find they take advantage of the plus/minuses with SAAMI specs.

    Don't apologize for the tape trick. I know gunsmiths who do it in a pinch.

  8. #18
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    Default Re: 8mm Headspace

    The mauser has a ton of safety built into it to keep the operator safe incase of a head separation. I would shoot it and examine the case. I think you'll be alright. I encourage everyone to buy the gauges.
    The Gun is the Badge of a Free Man

  9. #19
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    Default Re: 8mm Headspace

    Famous last words but I think your fine........Even with a tape approximation you are not massively out of spec and nothing close to blowing up.

    Just get a field gauge to check if you are out of spec. Unless you are reaming chambers you do not need a no go.

    Do you reload? If you do here is a totally hack suggestion........If this is your ONLY 8mm just neck size the cases or barely bump the shoulder when reloading. You will fireform the case to the exact size your chamber size on your first shot. It usually (again famous last words) takes repeated over resizing to get a case separation.

    The only downside is that your reloaded rounds should not be used in ANY other 8mm. They will not chamber and should be labeled as such. Congratulations. You are now fireforming and loading a Wildcat round.

  10. #20
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    Default Re: 8mm Headspace

    Bolt action not auto loader advise ^^^^^^

    I have had a fn49 rip the 8mm in half on 2 different factory new rounds. Big boof and shock wave, no damage to me, springs crunched on rifle.
    The Gun is the Badge of a Free Man

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