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Thread: Correct pin size for Bren/L4 gas block retaining pin?

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  1. #1
    Member Richard-'s Avatar
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    Correct pin size for Bren/L4 gas block retaining pin?

    Does anyone have on hand the correct size or spec for Bren / L4 gas block pins?

    The pin hole in the barrel is still under sized and the pins we sourced are dropping halfway through.

    Looks like I will need to source some locally, so it would be good to know the size/taper I am looking for...



    Other than that, the L4 barrels are going very well and are almost done.
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    If it were me, personally and not really knowing what you're doing or new or using of old (making new or converting old barrels to 7.62mm?) I'd start from afresh. Looks like you are using old gas blocks so I'd drill (ouch........) and ream to the new morse taper pins that you have obtained locally

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    Member Richard-'s Avatar
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    Thread Starter
    Sounds like the way to go, thanks.

    They're new 7.62 barrels, using as new L4 barrel fittings.

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    Really Senior Member Joe H's Avatar
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    Richard,

    Here is a cut from a MK II receiver drawing. Notice it is reamed at assembly. I would follow Peter's advice and ream it to the nearest size standard taper pin.

    Joe
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    Member DOD 7.62's Avatar
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    Looks like I might be responsible here, I supplied Richard the pins in question, they came out of my Box of Bren parts but appear to be the wrong ones. Can anyone identify them?
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  9. #6
    Really Senior Member Joe H's Avatar
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    DOD,

    I think the L1A1 was adopted by the UKicon in 1957. Maybe they are the pins for the L1A1 gas block???

    Joe

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    Really Senior Member Brit plumber's Avatar
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    It may be worth considering that the fastest way to remove the locking pin to drill them out. I see you said 'as new fittings', is that 'New' or salvaged from nearly new barrels? It could be that those holes are now slightly oversize and need the next size up taper anyway.

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    Those pins are from the gas CYLINDER to the body. As I understand it, Richard wants the pins from the gas BLOCK on the barrel! Joe confused things a bit but that aside, we both agree we'd start anew.

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    Really Senior Member Joe H's Avatar
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    Sorry Guys Starting Over,

    Gas Block to L4 barrel ".162" Dia. ream at assembly". I think I'd still stick with Peter's recommendation. Ream for a new tapered pin. Tapered pins are much easier to get out if necessary. Does "ream at assembly" on the drawing mean ream for a tapered pin at assembly ?

    Joe
    Last edited by Joe H; 05-26-2017 at 11:53 AM.

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    Yes Joe, taper pin. Both the L4 and .303 are the same as the L4 used .303" gas blocks taken off .303 guns. In case anyone doubts this, ask yourselves why L4 barrels came with Mk1 and 2 type gas blocks and with different makers markings including CRD and JI etc. As an aside, drilling half a diameter - as in this case, through half the taper pin hole diameter occupied by the barrel is fraught with danger for many technical reasons

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