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Discussion in 'General Gun Discussions' started by The Deer Hunter, Dec 28, 2006.

  1. The Deer Hunter

    The Deer Hunter New Member

    My friend asked me what a calibre is. Is it just the measurement in decimals of an inch?

    Also what is a gauge? I recall reading about how a gauge is measured. I think its something like lead round balls with the bore measurement...

    So please inform me.

  2. isp2605

    isp2605 New Member

    Correct and it could also be millimeters.

    You got it about gauge. It's the number of lead balls the diameter of the bore equal to 1 lb. So a 12 gauge would be 12 lead balls the size of the bore to equal 1 lb. 20 ga would be 20 lead balls the size of the bore. 10, 16, 28, etc figured the same way.
  3. stoky

    stoky Member

    Caliber is as you say, the bore diameter in inches or millimeters.
    Gauge is how many lead balls that size it takes to add up to a pound. (.410 excepted)
  4. Froggy

    Froggy New Member

    Spot on.

    And since we know the "weight" (specific gravity) of lead, you can convert them:

    12 gauge --> 0.729"

    20 gauge --> 0.615"

    28 gauge --> 0.550"
  5. gbran

    gbran Active Member

    Then there's the oddball 410.
  6. Avenger

    Avenger New Member

    I've always thought that, at least in engineering terms, calibre is the ratio of bore and barrel length, or bore and chamber length for the cartridge.
  7. ArfinGreebly

    ArfinGreebly Moderator Emeritus

  8. RKellogg

    RKellogg New Member

    I had an old timer tell me that the 28 ga was the perfect gauge , mathematically . He also said the same about the 7mm mag . Any one care to explain why .
  9. deadin

    deadin Active Member

    That's true if you're talking about naval guns. (Like a 5 inch 58). I've never seen it applied to small arms.

  10. isp2605

    isp2605 New Member

    You should have asked him. It was his story.
  11. deadin

    deadin Active Member

    To confuse the "bore diameter" issue. Some are the diameter measured to the grooves (i.e. .308) and some are the diameter measred to the lands. (i.e. .303 British).:evil:

  12. JesseL

    JesseL New Member


    And some have very little to do with any real measurements at all. .380 ACP is .355", .38 Special is .357", .44 Special and magnum are .429", and most 32s are actually .308-.311".
  13. deadin

    deadin Active Member

    Some of those can be explained (original heel seated bullet diameters, etc.)
    Some are beyond explaination.;)
    That's why I keep a copy of "Cartridges of the World" on hand.:D
  14. DoubleTapDrew

    DoubleTapDrew New Member

    Isn't "calibre" the English spelling and "caliber" American? Kind of like tire and tyre?

    It's funny when talking to newbies about calibers and how 380 or 357 sound massive compared to 38 or 32 until they realize there's a decimal in front of there.

    What caliber is the phased plasma rifle in the 40-watt range? :p
  15. CWL

    CWL New Member

    Guage and bores of firearms was originally determined 500-600 years ago, that is why it seems so strange to us today.

    The weight of shot was originally determined in the 15th-16th Centuries using Imperial Roman weight measurements. This was the only uniform measurement for weight back then because each country, duchy, county, town & village could have it's own method of measurement. One pound of lead could be divided into 1/20, 1/16, 1/12, 1/10 etc. these measurements determined the size of a bullet and the bore diameter (guage) necessary for the arquebus, musket and pistol made by any gunsmith. This also explains how pistol calibers came about: .36 = 86 balls/lb; .44 = 48 balls/lbs.
  16. Mannlicher

    Mannlicher New Member


    well, with naval guns, caliber refers to the length of the barrel. The US 16 inch guns on the Iowa Class BB for example, are 16", 50 caliber. The barrels are 67 feet long.
  17. Mal H

    Mal H Administrator

    It is around 6600 angstrom units, give or take a few hundred. :p :p
  18. GunnySkox

    GunnySkox New Member

    One thing I noticed about gauges is it's sort of like the fractional end of the "pounder" system used for smoothbore cannon. Observe:

    A smooth-bored cannon called a "three pounder" has a bore of a size that fires a projectile of a certain composition and form which weighs, you guessed it, three pounds.

    A smooth-bored arm called a "twelve gauge" has a bore of a size that could fire a projectile of a certain composition (lead) and form (sphere) which weighs, and here's the style, 1/12 of a pound.

    Am I right?

  19. 45crittergitter

    45crittergitter New Member

    Note that caliber by definition is the expression of diameter in decimal parts of an inch. For example, it's "44 caliber," not ".44 caliber," as the decimal point is redundant with the word "caliber."
  20. Billll

    Billll New Member

    Here is a gauge/caliber chart:
    Gage Ball dia
    425 0.220
    290 0.250
    169 0.300
    140 0.319
    100 0.357
    66 0.410
    53 0.441
    50 0.450
    28 0.545
    20 0.610
    16 0.657
    12 0.723
    10 0.769
    8 0.828
    6 0.911
    5 0.968
    4 1.043
    3 1.148
    2 1.314
    1 1.656
    0.75 1.822
    0.5 2.086
    Note where some of the more popular calibers fall, 45, 357, 410, 44.
    The density of 'lead' varies a bit with alloy, so if you set up a spread sheet to calculate this, keep it in mind. These sizes are not absolute.

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