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Thread: NO1 MKIII gap between bolt head and bolt bodyHi a

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    Member NVGuy's Avatar
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    NO1 MKIII gap between bolt head and bolt bodyHi a

    Hi all, I have a couple of barreled actions I am working on building up into complete rifles. I am trying to headspace them at this point. I have picked up a few bolt bodies and bolt heads to do this. I install the bolt head onto the bolt body and threads it in until it stops leaving no gap between the bolt heads and bolt body. when i back the bolt head off to line it up there is a gap. Does this sound right? My other rifle that i have completed does not have this gap between the bolt head and body.


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    Advisory Panel browningautorifle's Avatar
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    Pics would help to show how much gap you see...
    Regards, Jim

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    Member WillSarchet's Avatar
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    I believe the correct way to test this is to screw the bolt head on tight, then measure how much it overclocks past the rib. It should be within 20° if I recall correctly.

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    Really Senior Member Alan de Enfield's Avatar
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    No, the gap is incorrect. as Will says, this is called 'over clocking' (or 'overturn') and only a few degress is allowed.
    If you have the 'gap' as soon as you fire the rifle the threads will take the recoil Instead of the bolt body) and it 'hammers' the threads until the bolt head is moved back to the bolt body & this increases the headspace.

    Clocking is just as important as headspace, and it can take you 'dozens' of bolt heads to find one that 'clocks' correctly AND headspaces correctly.
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    Last edited by Alan de Enfield; 11-09-2020 at 04:28 AM.
    Mine are not the best, but they are not too bad. I can think of lots of Enfields I'd rather have but instead of constantly striving for more, sometimes it's good to be satisfied with what one has...

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    Thread Starter
    Here is a picture of the gap i am speaking of.


    Bolt-head

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    Yeah...you're actually a full turn or something out. That's what I thought you meant. Not a little bit... Something's way out of whack there.
    Regards, Jim

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    Really Senior Member Alan de Enfield's Avatar
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    Just a thought.
    There are two types of bolt heads for the SMLE.

    One which has a 'slot' cut into the threads, and one which doesn't.

    The one with the slots is an early version which had a different striker and the slots in the threads engaged with the striker to allow you to uncscrew the striker (sort of a built in spanner). The slotted bolt head will not screw all the way into the later barrel body and 'jams' a couple of threads proud of being properly fitted.

    You need to ensure that your Bolt head, striker and bolt body are all 'matching' properly, if you have (say) and 'old' bolt head with a 'new' body and a 'new' striker it will not assemble. All 3 parts need to be compatible.

    Posted in another thread a few days ago by Bear43
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    Last edited by Alan de Enfield; 11-10-2020 at 04:22 AM.
    Mine are not the best, but they are not too bad. I can think of lots of Enfields I'd rather have but instead of constantly striving for more, sometimes it's good to be satisfied with what one has...

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    Clearly it's best practice to have as little over-turn as possible for primary extraction if nothing else, but if one stops and considers the fact that the threaded portions of the bolt head and bolt body are of the same steel as the shoulders, and apparently not heat treated differently, it is pretty clear that the load from firing even if taken entirely on the threads, is spread out over the contact surfaces of 12 or more turns of thread - if they are of the exact same pitch, and there seems to be no reason why they wouldn't be, even with severe wear on one or both -the distributed load per square ___ should be a small fraction of what it would be on the shoulder if that was the only contact surface.

    A bit like thrust on an interrupted screw breech.

    If the parts were in a position that caused them to slam into each other on firing, that would be a different proposition of course.

    Peter once told me that max. acceptable overturn on the L42 was 12 degrees.
    Last edited by Surpmil; 11-10-2020 at 11:11 AM.
    "Men occasionally stumble over the truth, but most pick themselves up and hurry off as if nothing had happened." W.L.S.C..

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    Really Senior Member Alan de Enfield's Avatar
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    Quote Originally Posted by Surpmil View Post
    Clearly it's best practice to have as little over-turn as possible for primary extraction if nothing else, but if one stops and considers the fact that the threaded portions of the bolt head and bolt body are of the same steel as the shoulders, and apparently not heat treated differently, it is pretty clear that the load from firing even if taken entirely on the threads, is spread out over the contact surfaces of 12 or more turns of thread - if they are of the exact same pitch, and there seems to be no reason why they wouldn't be, even with severe wear on one or both -the distributed load per square ___ should be a small fraction of what it would be on the shoulder if that was the only contact surface.

    A bit like thrust on an interrupted screw breech.

    If the parts were in a position that caused them to slam into each other on firing, that would be a different proposition of course.

    Peter once told me that max. acceptable overturn on the L42 was 12 degrees.
    On 4th December 2007 he posted this :

    (A brief extract of the long post)

    The bolt head should not overturn the long/top locking shoulder by more than 16 degrees but if you have a No4T or L42, it should not overturn buy more than a 'few' degrees. Mine were always 'in line' through selective fitting but you won't have a big tray of bolt heads to select from! The reason for this is because over a 'few' degrees (it doesn't define 'a few' but use 2 or 3 as your MAX), the recoil is taken on the bolt head and bolt threads. That is OK, but on an accurate No4T and L42, we want the recoil to be taken on the face of the bolt and transmitted radially, down through the bolt head and onto the front flat surface of the bolt body that mates up to the bolt head. Got it?

    In discussions at the time, it was Peter that told me about the threads getting 'hammered' and increasing the head space.
    Last edited by Alan de Enfield; 11-10-2020 at 11:26 AM.
    Mine are not the best, but they are not too bad. I can think of lots of Enfields I'd rather have but instead of constantly striving for more, sometimes it's good to be satisfied with what one has...

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  17. #10
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    Quote Originally Posted by Alan de Enfield View Post
    On 4th December 2007 he posted this :

    (A brief extract of the long post)

    The bolt head should not overturn the long/top locking shoulder by more than 16 degrees but if you have a No4T or L42, it should not overturn buy more than a 'few' degrees. Mine were always 'in line' through selective fitting but you won't have a big tray of bolt heads to select from! The reason for this is because over a 'few' degrees (it doesn't define 'a few' but use 2 or 3 as your MAX), the recoil is taken on the bolt head and bolt threads. That is OK, but on an accurate No4T and L42, we want the recoil to be taken on the face of the bolt and transmitted radially, down through the bolt head and onto the front flat surface of the bolt body that mates up to the bolt head. Got it?

    In discussions at the time, it was Peter that told me about the threads getting 'hammered' and increasing the head space.

    I fit mine to have little or no overturn also, for maximum primary extraction and also because when the bolthead is "tight" in the body of the bolt there is the least possible amount of movement between the two parts.

    As we all know from slow motion videos etc. recoil is only the beginning of the motions that a weapon being fired undergoes, albeit the most violent and abrupt.

    The less potential for movement there is, the less potential for "slamming", wear and distortion over time.

    IMHO.
    Last edited by Surpmil; 11-11-2020 at 02:09 AM.
    "Men occasionally stumble over the truth, but most pick themselves up and hurry off as if nothing had happened." W.L.S.C..

    "None need deceive a people determined to deceive themselves."

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