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    Replacing that awful BSA breech pin with a bolt?

    Hi all,

    Thinking out loud on this one, I have far too many projects to be getting on with (plus other stuff), but as this would be hopefully getting done (I haven't asked him yet though) by my local guru engineer, I have a BSA Lightning mk1 that I obtained from Chris at one of the bashes, now then if I was to fit a breech bolt, which bolt do you think would be the best to go for, I personally think the BSA one looks neat and tidy and seems to do the job on my Mercury's and Supersport custom but I've read that all it does is pull the breech block to one side of the jaws?, I've seen the HW bolt conversion done on a Mercury, which I expect does the job nicely but looks ugly to me because it sticks out the side and requires the stock to be altered or do I go the Diana route with the hollow pin and bolt arrangement but still does the same as the HW, or is there another bolt setup I don't know about?

    Your thoughts please chaps.
    Far too many rifles to list now, all mainly British but the odd pesky foreigner has snuck in

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    Get a HW95 breech bolt, nut and shims.

    HW95 cylinder, barrel, piston, end block, Rekord trigger......yep....bin it off and get a 95, Pete.


    On a serious note, although it would entail some re-engineering work, go the HW bolt route.
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    Quote Originally Posted by look no hands View Post
    Hi all,

    Thinking out loud on this one, I have far too many projects to be getting on with (plus other stuff), but as this would be hopefully getting done (I haven't asked him yet though) by my local guru engineer, I have a BSA Lightning mk1 that I obtained from Chris at one of the bashes, now then if I was to fit a breech bolt, which bolt do you think would be the best to go for, I personally think the BSA one looks neat and tidy and seems to do the job on my Mercury's and Supersport custom but I've read that all it does is pull the breech block to one side of the jaws?, I've seen the HW bolt conversion done on a Mercury, which I expect does the job nicely but looks ugly to me because it sticks out the side and requires the stock to be altered or do I go the Diana route with the hollow pin and bolt arrangement but still does the same as the HW, or is there another bolt setup I don't know about?

    Your thoughts please chaps.
    I've got one of each ready for when I find an engineer. The jaws would have enough material to machine out a hole for the BSA bolt. Why doesn't it pull Mercury's out? that seems a bit odd to me.
    I would want the jaws machined on both sides so that the HW bolt would sit as flush as possible then cut to length. I will have to shorten the bolt 'cos it's for a Meteor.
    Last edited by Dornfelderliebe; 17-02-2024 at 08:52 AM.
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    Quote Originally Posted by Dornfelderliebe View Post
    I've got one of each ready for when I find an engineer. The jaws would have enough material to machine out a hole for the BSA bolt. Why doesn't it pull Mercuries out? that seems a bit odd to me.
    I would want the jaws machined on both sides so that the HW bolt would sit as flush as possible then cut to length. I will have to shorten the bolt 'cos it's for a Meteor.
    The Mercury bolt does not lock/thread into the breech jaw, it just has a nut and no locknut.
    The result is that the pinch of the locking chisel rotates the bolt while cocking, ant it tends to work loose/unscrew.
    On the HW, the bolt threads into the "opposite" fork of the jaw, so the nut works as a locknut.
    Too many airguns!

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    Hmm tapping threads eh? I'll go with the HW item.
    The more I think I know, the more I realise the less I know.

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    Quote Originally Posted by Dornfelderliebe View Post
    Hmm tapping threads eh? I'll go with the HW item.
    The HW version will need a lot more machining.
    The Mercury bolt should be easier to fit.
    Too many airguns!

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    Quote Originally Posted by evert View Post
    The HW version will need a lot more machining.
    The Mercury bolt should be easier to fit.
    With a Meteor the hollow jaws will need filling and I wonder whether weld/braise or proper metal filler would do.
    Any way the Mercury bolt looks much better.
    The more I think I know, the more I realise the less I know.

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    Replacing that awful BSA breech pin with a bolt?

    Quote Originally Posted by evert View Post
    The Mercury bolt does not lock/thread into the breech jaw, it just has a nut and no locknut.
    The result is that the pinch of the locking chisel rotates the bolt while cocking, ant it tends to work loose/unscrew.
    On the HW, the bolt threads into the "opposite" fork of the jaw, so the nut works as a locknut.
    Yep it's also a smaller diameter than the pin so would need a sleeve turning up to make it fit, the HW bolt is a much better solution. My 635 magnum i had the nut was always coming loose but the challenger i have now with the same hinge bolt arrangement does not for some reason.

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    Quote Originally Posted by junglie View Post
    Yep it's also a smaller diameter than the pin so would need a sleeve turning up to make it fit, the HW bolt is a much better solution. My 635 magnum i had the nut was always coming loose but the challenger i have now with the same hinge bolt arrangement does not for some reason.
    Non of the bolts have come lose on any of mine, I just think there may be more work involved with fitting the BSA bolt as where the bolt head and nut are recessed into the cylinder, I think the HW bolt sits on flats on the cylinder but I may be wrong.
    Far too many rifles to list now, all mainly British but the odd pesky foreigner has snuck in

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    Quote Originally Posted by look no hands View Post
    I just think there may be more work involved with fitting the BSA bolt as where the bolt head and nut are recessed into the cylinder, I think the HW bolt sits on flats on the cylinder but I may be wrong.
    The HW bolt measures 7mm, the BSA bolts are 6,35mm/.25". So the holes have to be reamed for the HW bolt.
    The HW bolt need extra fine threads cut into one side of the breech jaws.
    The Mercury bolt just needs recesses, definately less work.
    Too many airguns!

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    Quote Originally Posted by evert View Post
    The Mercury bolt does not lock/thread into the breech jaw, it just has a nut and no locknut.
    The result is that the pinch of the locking chisel rotates the bolt while cocking, ant it tends to work loose/unscrew.
    On the HW, the bolt threads into the "opposite" fork of the jaw, so the nut works as a locknut.
    The above is spot on. The HW system is far superior. Bowkett used to copy it on his BSA Meteor, Mercury, W&S conversions in the 1980's.
    The other advantage of the HW system is that the bolt cannot rotate when the rifle is cocked. This results in a "cam" action when the bolt/pin rotates and causes additional problems.

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    Quote Originally Posted by greenwayjames View Post
    The above is spot on. The HW system is far superior. Bowkett used to copy it on his BSA Meteor, Mercury, W&S conversions in the 1980's.
    The other advantage of the HW system is that the bolt cannot rotate when the rifle is cocked. This results in a "cam" action when the bolt/pin rotates and causes additional problems.
    What he said.

    I think the conversation between management and the engineers at BSA went something like this -

    Management

    "Lads, the customers and those picky pricks at the Airgun World are complaining about the jaws spreading on the Mercury"

    Engineers "They can buy an Airsporter, mebbe an Airsporter S, if that's the upgrade they're after"

    Management "Now lads were're losing out to these German fellows, no-one remembers the War any more, they're buying from them"

    Engineers "Send the Peaky Blinders round to that airgun comic, teach them who won."

    Management "Fix the jaws spreading on the Mercury, no more out of you or we'll move the operation to Spain"

    Engineers "Grumble grumble where's the calipers?"

    So instead of designing a good, precise, efficient breech they went with a solution that just 'stopped the jaws spreading'. It's odd because I think the breech lock up on BSA Mercurys and Meteors is really solid while being easy to unlatch, so theres the verticle, but laterally they just couldn't be bothered, twice. Strange British approach to things, so many things like the barrel and overall design were great on the Mercury.

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    Quote Originally Posted by Hsing-ee View Post
    What he said.

    I think the conversation between management and the engineers at BSA went something like this -

    Management

    "Lads, the customers and those picky pricks at the Airgun World are complaining about the jaws spreading on the Mercury"

    Engineers "They can buy an Airsporter, mebbe an Airsporter S, if that's the upgrade they're after"

    Management "Now lads were're losing out to these German fellows, no-one remembers the War any more, they're buying from them"

    Engineers "Send the Peaky Blinders round to that airgun comic, teach them who won."

    Management "Fix the jaws spreading on the Mercury, no more out of you or we'll move the operation to Spain"

    Engineers "Grumble grumble where's the calipers?"

    So instead of designing a good, precise, efficient breech they went with a solution that just 'stopped the jaws spreading'. It's odd because I think the breech lock up on BSA Mercurys and Meteors is really solid while being easy to unlatch, so theres the verticle, but laterally they just couldn't be bothered, twice. Strange British approach to things, so many things like the barrel and overall design were great on the Mercury.
    I was told by someone that knows the thinking at the time, pre- El Gamo Anglo/Spanish buyout, was that the vertical lock up due to its design centred the barrel in the jaws when the rifle was cocked so unless it was actively pulled to one side or the other when firing it would not make any significant difference to accuracy.
    The barrel vertical lock up design is one of the best of any breakbarrel air rifle. One of many brilliant designs by the late Mr Roger Wacrow.

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