A story in one bullet

In 1860s America the percussion revolver was the prominent fighting handgun. The 44 caliber, or “44/100ths calibre” was so named at the time because of the gun’s bore. Today we tend to use groove diameter to define caliber, but then why does a modern 44 use a .429″ bullet and a 38 use a .357″ bullet?

Much of the answer lies in this one bullet. When the 44 caliber percussion revolver was converted to fire metal cartridges, it presented the following challenges. The cartridge case of course had to fit into the percussion cylinder chambers, and had to fire a bullet of around .452″ to fill the grooves in a 44 caliber bore. SO the metal case had to fit inside a .452″ or so chamber, and fire a .452″ or so bullet, AND therefore the bullet had to have a heel base of around .429″ to fit inside the metal case. Such is the 44 Colt cartridge. It was built for cartridge conversions of percussion cylinders. It’s a 44 caliber because of the naming convention of the time which went by bore, rather than groove diameter, it uses a .452″ bullet and has a .429″ heel to fit in the case.

From that transition cartridge we see the seeds of how a modern “44” came to have a .429″ bullet. A similar thing occurred with the conversion of 36/100ths calibre percussion revolvers, and that’s how a 36 used a .380″ bullet and how a modern 38 uses a .357″ bullet.


13 thoughts on “A story in one bullet

  1. Nice explanation. I am confused by the terms “bore” and “groove diameter”. Is bore measured across the tops of the grooves, and groove diameter across the valleys? I.e., to use terminology from screw threads, bore is the minor and groove diameter the major diameter?

    • In bullet terminology they are also called lands and grooves which is a little more clear. Read more here.

      But yes. You are correct.

  2. I get it. The lands are the bore diameter, and the groo\/es are added after the bore is made.

    • Yes, well at least with cut rifling. You’re correct to point out the chronology there, because that explains the original use of bore diameter to define “caliber”.

      Originally of course there was no such thing as rifling. A gun’s bore was it’s bore, was its caliber, and that’s all there was to it. (we won’t get into the Naval definition of caliber) Then rifling began to be added, and people experimented with different groove styles and depths, but the bore was still the bore.

      • True. Flintlock Kentucky Rifles began to show up in the War for Independence, but most guns at that time were smoothbores. And the cut groo\/es we see today are not the only style of rifling. Glock, for instance, uses polygonal rifling.

  3. Pingback: SayUncle » A story in one bullet

  4. Thanks for that explanation.

    I remember reading about gauge definitions in shotguns, but my brain deleted the content some time ago.

    And if anyone could explain also the difference between a northerly wind and north wind and a northerner, I’d appreciate that, too.

    • Don’t know about the northerly north northerner thing. I suspect you may be a “northist” though.

      Shotgun gauge is very simple, and again it harkens way, way back. the gauge is the number of bore-diameter balls of lead that make one pound. 410 is the exception, as it is defined by diameter, directly.

      In fact, projectiles and projectile weights for rifles and pistols were routinely defined by the number of rounds per pound right up until the proliferation of the metal cartridge, and the practice hasn’t ever totally died.

      • Rifle bores were also sometimes defined by the gauge system, so you might take your four bore out to get you an elephant or a Cape buffalo. Or you might see an old letter wherein the proud owner of a longrifle would mention his firing a ball of “thirty eight to the pound”. They would aften refer to their rifle as “she”. Also a grain (one seven thousandth of a pound) might be referred to as a “corn”, as in “She burns three corns in her flashpan to good effect”.

  5. And it worked, too, until “they” decided to go with an inside lubricated bullet. I can’t remember which, Colt or S&W, reduced the bore diameter first while the other company initially relied on upsettage to fill the grooves. (And then there’s the .38 Smith & Wesson at .361 which went the opposite direction of history.) It’s interesting stuff.

  6. Ok, I get the 44 => .429 and 38 => .357 thing, but 36 => .380? Am I reading that right? Following your comments I would’ve expected 36 to be around .337″ (bore-.023, with the bore of a 44 = .452).

    • The 36 I mentioned is the “36 caliber” percussion revolver, which, like the 44 of the same period, was a measure of the bore diameter. It’s a different naming convention compared to “most” caliber naming today, which tends to go by groove diameter (.308, .223, etc). Hence a “36 caliber” percussion revolver had a bore of around .36 and a groove diameter of around .380.

      No need to overthink it. As is stated below, caliber names are often all messed up. Marketing playes a role no doubt, as does the need to avoid confusing one cartridge with another in the same general bore size.

      I was just fascinated with that one bullet I linked to, because it’s a “45” by our modern naming standard, it’s for the “44 Colt” cartridge which is fired from a “44” conversion pistol, and it has the .429″ heel, which became the standard size of a modern “44”.
      All three numbers (44, 45 and .429″) are represented in one bullet. Pretty cool. So I see it as the “missing link” (but it was never missing) between the old and the new 44s and 36s.

      Thus the very short period in which cartridge conversions were popular in America seems to have led to the rather odd naming-verses-sizing that we use today in the “44” and “38” calibers.

  7. .357, .38, 9mm. .380, are nominal, names of the rounds, not what a micrometer would show. Your .380 ACP is actually a .355. That should be the groove to groove diameter of your barrel. Your land to land diameter should be about .02 mms less, or .335. (Don’t quote me on the actual numbers, barrels vary.) A tight squeeze with the bullet engraved to fit into both the lands and grooves. Think of a kind of a dovetail.

    Going back to the cap and ball pistols, that was the other way around. .36 was the land to land diameter and .38 was the groove to groove diameter of the barrel. The ball was .38 in diameter. When forced into the grooves, it was engraved to accommodate lands of .36 . If you pushed a lead ball gently through your cap and ball’s barrel and then you miked it, you’d get a reading of .36 on the part that touched the lands and .38 on the part that touched the grooves. (Don’t quote me on these numbers either, for the same reason.)

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