British double rifle gauge to caliber conversion

Discussion in 'Firearms & Ammunition' started by ikeda, May 7, 2019.

  1. ikeda

    ikeda AH Veteran

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    In my study since acquiring an H&H double I've run across three different proofed bore diameters for the .50 BPE guns.
    So far I've read about guns having 38 gauge, 39 gauge and 40 gauge bores.
    Can anyone actually tell me what were the industry standard bore and groove diameters for these three different gauge barrels? Assuming there actually an industry standard in 1885.
     

  2. AZDAVE

    AZDAVE AH Elite

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    You will find that almost every maker in the British gun trade had their version of the better mouse trap. You will find many different bore diameters with no real standard per say I have seen 500BPE doubles with as small at .499 to as larger a .515. Alott of the rifles were built and enough ammo to keep the owner shooting for a good bit of time. During that time period H&H didn't manufacture their own guns. The did the final fitting and regulation but the major part of building the rifle they outsourced.
     
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  3. ikeda

    ikeda AH Veteran

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    If the gun is proofed and marked as 38, 39 or 40 gauge then there must have been a standard inches dimension to go by.
     

  4. bruce moulds

    bruce moulds AH Fanatic

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    gauge in relation to rifle barrels is defined by the no of lead balls to the pound in that diameter.
    what complicates the issue is how the ammunition was loaded.
    many, either round ball or conical bullet, used paper patches, and the thickness of paper could define the diameter of the projectile.
    this was further complicated by grease groove bullets with no patches.
    then individual makers had different ideas on chamber and throat configurations.
    black powder expresses had to be loaded clean or dirty, and those old dead guys expected to do that 10 times before cleaning.
    this often meant having a slightly larger barrel dimension to allow for fouling, and a tapered throat for same.
    on top of this manufacturing tolerances were not as close as today.
    bruce.
     

  5. ikeda

    ikeda AH Veteran

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    Well what I do know for sure is that my H&H is marked with 40 meaning 40 gauge and it has a groove diameter measured quite carefully, more than once, of .505". This was done by pushing a soft lead slug through the entire bore. During this process, starting from the breech end seemed to indicate that the throat, the first inch or so, seems to be tapered.

    A .512" lead slug will start in the breech end and go about an inch in before it gets quite tight. The effort to push a lead slug on thru the barrel is quite consistent.

    The bore of a 40 gauge barrel "should" measure about .488" but these measure .497". The bore diameter is more difficult to measure and my hand shakes more than it use to, but I'm pretty confident of the .497" measurement.

    This means that my total groove depth is .008" or .004" per groove. This does not sound like a lot, but this gun is teaching me a lot of new tricks.

    I've shot some .505" 525gr Woodleigh bullets thru the chronograph, and behind a load of 58/4198 turned in a velocity of 1597 fps. I haven't had a chance to shoot it on paper yet. I've also got some .505" 400gr and 440gr Hawk custom bullets on the way. I think these weights will work out better than the heavier ones.
     
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  6. sierraone

    sierraone AH ENABLER SILVER SUPPORTER AH Legend

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    Google "Firearms Gauge measurements from the 1880s". This will give you info and charts on how to do conversions to more modern measurements.
     

  7. bruce moulds

    bruce moulds AH Fanatic

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    ikeda,
    thank you for the post.
    0.004" groove depth was called shallow rifling, and was considered to hold less black powder fouling, as it allowed it to blow out the muzzle with nowhere to be trapped.
    is the rifling square or of some other configuration?
    interesting about the tapered throat.
    bruce.
     

  8. ikeda

    ikeda AH Veteran

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    The grooves seem to be a quite conventional square shape....the barrel has 6 grooves.
    Interesting observation....the left barrel seems to have been shot a lot more than the right, which generally goes against the common perception of the right barrel getting shot the most.
     

  9. bruce moulds

    bruce moulds AH Fanatic

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    thanks again.
    bruce.
     

  10. ikeda

    ikeda AH Veteran

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    My .505" 440 gr Hawk bullets arrived and here are the results so far.
    50gr SR4759 1743 fps
    56gr Accurate 5744 1744 fps
    59gr IMR 4198 1634 fps
    61gr IMR 4198 1723 fps
    Estimated pressure of the loads are less than 9.0 Tons
    Hopefully I'll have a chance to do some regulation shooting soon.
     

  11. flatwater bill

    flatwater bill AH Elite

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    Old H&H letter to a customer wanting an 8 bore after they had discontinued them, "Our 10 bore is quite large, actually closer to a 9 bore, and should meet your needs"......AZ dave is exactly right...........lots of variability from maker to maker.....but your 40 bore is spot on .488 tube that was then rifled. BTW...........I wouldn't scrape too many jacketed bullets down that bore unless they were Hawk bullets which are "dead soft".......FWB
     

  12. ikeda

    ikeda AH Veteran

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    The problem is that my 40 gauge is not .488" it is .497" bore diameter, and .505" groove diameter....go figure.
     

  13. flatwater bill

    flatwater bill AH Elite

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    Aaaah, well, that just gives you a few more bullets to shoot. Hawk makes a great bullet for the Gibbs..........FWB
     

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