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Thread: 1898 Headpsace Out of Whack

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    Contributing Member 22SqnRAE's Avatar
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    Quote Originally Posted by Patrick Chadwick View Post
    Finally, gauge sets should have a "go" gauge, a "no-go" gauge, and finally a "field" gauge. I have suggested above, that military rifles will frequently accept a "no-go" gauge, because of the combination of initial manufacturing tolerances and a century or more of wear. But a failure with a "field" gauge (i.e beyond that acceptable for a active service rifle) would be a more serious indication that something is wrong.
    G'Day Pat, a great response, overall. As an Enfielditis carrier (I don't suffer from it... I breed it) I concur with your assertions of how the .303 case changes. Dramatically, in many perfectly serviceable rifles.



    I would like to, politely and gently disagree with you on one of your points.

    Your last paragraph is generally agreeable, but the 'Field' gauge, I suggest, with all due respect is another modern invention, as are SAAMI specs, which do not bear accurate resemblance to the original Military or Government Supply specifications of the various calibers they purport to represent. Note, with respect to the Yanks, that the Association that agreed on what they would make is entirely composed of United Statesicon firearms and ammunition manufacturers. For the thinking person, that fact alone should cause concern.

    Let's take the .303, which I am intimately familiar with, about 25 units over... The Service specification for the head space, as per Instructions to Armourers and what Peter Laidlericon continually cites is: GO = 0.064" NOGO = 0.074"

    That's it.

    No 'Field' gauge - which is a fabricated range legend. Now for the argumentative types, please refrain from "but, but, what about the Vicker's MG gauge?..." Not relevant. We're specifically talking about the tolerance on a standard Service Rifle with standard Ball ammo.

    The 0.067" (or sometimes cited as 0.068") gauge that crept into modern legend came from the Civilian Target Shooting fraternity, you know, the Bisley types. These fellows were dedicated to eliminating as many variables from their shooting to ensure highest possible repeatable score. One of the things they did, was to measure the thickness of the rims of their Service Issued (well, sourced) cartridges and group them in lots of thou increments. The idea here was consistency within serials (series of 10 or 11 scoring shots.) Having all the same dimension cartridge rim, there would be minimal head space difference causing changes in shot placement. So, this very particular and fastidious behavior crept into other areas. The smaller head space range than what the Service specifications set, became accepted within that group of shooters. What never changed because of the target shooter's fastidious decrease in tolerance, was the acceptance range of a serviceable .303 head space - still 0.064" to 0.074".

    Now what I do agree with Pat on, is the adoption of good and unacceptable limits. In the Krag (which is very similar to the .303) there was always a Service Specification of acceptable head space range from a low number to a higher number. Any other intermediate datum you wish to put in between does not change the "GO" and "NOGO" limits of Service specification. Field, whether people like it or not, is a modern construct not included in any Commonwealth (and I suspect US TM- ) doctrine. If you choose to use the upper serviceability headspace tolerance figure as your "Field" then I concur that that's a safe way to present your expectations in public, because it indicates you're choosing a lower limit for your 'NOGO' tolerance. That is safe.

    To round out, let's be clear that the NOGO head space was not an indication of absolute safety. It was a limit of practicality and most importantly, reliability. Can a rifle with oversize (out of tolerance) head space work safely? The answer is probably yes, most often. Is it reliable? Most probably not very. Will the cases be suitable for reloading several times? Maybe, maybe not... Patrick is absolutely spot on in drawing your attention to headspace alone as no means of determining the safety of a rifle body/action (I'll not go into the ongoing discussion about what to call the receiver group!)

    I hope this comment helps and does spark some thought among a few, at least. Thank you for reading.
    Last edited by 22SqnRAE; 11-16-2019 at 11:19 PM. Reason: spelling
    Trying to save Service history, one rifle at a time...

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