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    Member george1108's Avatar
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    k31 headspace question

    Since the bolt is separate from the locking lugs, how does the K31icon headspace?

    thank you for your answers.


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    There is no provision for adjusting headspace in the official K31 armorer's manual. Therefore, the K31 is headspaced from the factory.

    As long as the receiver, bolt and sleeve are matching, you're good. Headspace gauges are rare within the Swissicon Army, and a field expedient it to grab a new cartridge, dab a bit of grease and stick on a piece of shim stock. If the bolt closes on a shim of 0.2mm, the rifle is considered worn out. This rarely or never happens though, since the rifles are well made and well taken care of.

    If you are interested, I can send you the armorer's manual for the K31.

    MEERKOOS

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    Contributing Member Eaglelord17's Avatar
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    It headspaces the same way every other rifle does, on the bolt face. Just because the locking lugs aren't part of the bolt face doesn't mean it headspaces differently. Your overthinking this

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    Senior Member RC20's Avatar
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    Per above. The term Military rifles and headspace is a nebulous thing as the intent was not to meet SAAMI spec but have a combat rifle that works in the mud, snow etc.

    The simple reality is head space is on the shoulder. WE measure that in terms of distance from the bolt face to the shoulder (all math where but its a defined point on the shoulder)

    So, I am going to ramble on a bit, I like to pass on what I have learned. To the best of my knowledge the information is solid.

    So, to start with, I picked up a K31 with a great deal of thanks to a member of this group.

    I am also setting up to have a Savage Rifle chambered in the 7.5 x 55 Swissicon chamber (I am going to shoot it a lot and would rather shoot out a $550 barrel than a K31 that can't be replaced).

    I either need a go and no go gauge ($80 or so) or I need to have a reference. I am using new PPU cartridge as my GO and a Fired PPU in the K31 as my NO GO.

    That fired case blew the shoulder out .015 from a new case. In the world where .005 is the difference between GO and NO GO and FIIEL REJECT, that is huge.

    Is there anything worn with the K31 chamber? Nope, brand new, boroscoped, tested with a 30 caliber threat erosions and muzzle wear gauge, rifling is solid, the lands are not fire cracked (and the should would not move anyway so it would be a bad factory build? -- nope, this is a K31, that does not happen (if it did they would have re-done it)

    The explanation is SAAMMI (or if its not SAMMI whoever) specked a nominal chamber based on a private owners gun, ak sportsman's, hunt er etc. Its not going to see combat and its not going to get combat dirty or combat shot.

    The K31 was intended to and it has a generous chamber to do just that.

    Also note that the K31 (and Mauser 8 mm I have seen) has a very short almost Short Magnum or Target shape shoulder. It does not grab nearly as much In the chamber and throat (where the neck lives). Good for combat and machine guns.

    It also happens to be what the modern target shooters have found to be a more optimal case shape! Good question is why the US has long case shoulders (or did) ? Not a clue. Contrary to all thoughts, the old 303 Britishicon worked despites it being rimmed, billions of rounds run though in both WWI and WWII and well past it in the Bren guns) US did not report issues with theirs. So who knows, but it is interesting.

    None of that large forward blown out shoulder (headspace) hurts anything, after all they were only intended to fire once, its us pesky collectors and enthusiasts that came on this all later and got technical .

    The reason its not more is you have to get the firing pin to push up against t something and not too far down the barrel or no bang (been there done that)

    My Model of 1917 30 Cal Enfield's are all the same. Almost go out to the end of so called Field Reject. Probably should be called firing pin failure gauge.

    Firing pin hits the case and the case moves forward until it hits the shoulder, then and only then will the firing pin dent the primer. Too much give (headspace) and no bang.

    My idea is to fire form the cases in the K31, and then set the Savage headspace to match (as I can do that on that gun with its nut) and we are good.

    That may not work if I don't have enough extension of the firing pin with that much shoulder bump out. I can adjust the firing pin for that if needed (at least on the older Savage design, new one is different).

    Otherwise I would simply set the Savage on a non fired case and have a tight head space.
    It is also likely a head space that not all ammo would fit into.

    As I am only blowing out the shoulder once, there is no issue with the case. It can more than handle that. Long term it gets anealed in 5 firings and reset.

    Another ways to check headspace is a new case and freezer tape on the back of a case. One layer is a NO Go Gauge, two or three layers if filed reject. My Savage armors CD shows them doing that.

    To a major degree head space has taken on a deeply felt meaning of mystery and quality.

    It really is not, the military sets it very loose for their good reasons and when we have a SAAMI or equal cartridge, they set it tighter for their purposes.

    If you move cases around between guns its important issue, either you wear the case out setting them all back or you split batches.

    It is an indication of quality control by a spring gun mfg. A long headspace indicates poor quality control and may be reflected in the rest of the gun or barrel or it may be a mistake. Ok if the firing pin works.

    To tight and you can't chamber new brass or cartridges.

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    Really Senior Member Aragorn243's Avatar
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    There actually is a problem with some K31icon's but I can't recall what it is off the top of my head. It is not headspace. It is semi-serious to the function of the rifle and involved a set period of production. It is correctable. Something is brittle and can crack and needs to be checked periodically if you have one made in that range.

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    k31 headspace question

    Due to material supply problems, on 1944 production rifles a different steel was used for the bolt operating rod which meant that the interrupter lug was prone to cracking and failure. As a result the Swissicon Arsenals replaced these on the offending rifles but there could of course still be some around that slipped through the net.

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    That's it, you have a better memory than me.

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