E.g. The bullet of 9×19 is 9mm wide but of a 5.56 isn’t 5.56
Edit: 5.56 not 55.6
In: Technology
So a 308’s bullet is .308 inches wide but a 7.62 nato’s land is 7.62mm. Why?
I know US calibers are sometimes measured by the groves but what about 9×19 and 5.7?
because they’re just names and people defined things differently. sometimes different calibers use a different diameter in the name despite being the same actual dimension, just to avoid confusion. there is no central regulating body for caliber naming and there certainly wasn’t 100+ years ago
It has mostly to do with origins. US uses inches, so American calibers are in inches. Most of the rest of the world uses metric, so their calibers are metric. 9×19 is European, 5.7 is European. .223 is American, but NATO is mostly European and adopted the 5.56.
There’s actually no such universal convention.
Classic examples:
9x19mm (aka 9mm Parabellum) has a *bullet* diameter of 9.01mm and a land diameter of 8.82mm
9x18mm (aka 9mm Makarov) has a *land* diameter of 9.00mm and a bullet diameter of 9.25mm
Both are pistol rounds.
It depends much more on the local custom at the time a round is created and as other people already mentioned, sometimes there are additional reasons like trying to avoid confusion with similar cartridges or basing it on other dimensions found e.g. on the case that lead to *neither* of those two measurements to be reflected in the caliber name. (.38 Special says hi! .357″ bullet and .346″ lands)
Everyone uses a mix of ammo calibers.
My very American pistol fires 9x19mm which was developed by an Austrian man named George Luger
But 9mm is a good caliber so it’s now a standard ammo type world wide.
This can be applied to almost every ammunition caliber in the world, some are great and you can probably list them off.
Others where one off ammo types used rarely. Like 8mm Mauser. It’s not used anymore really. But was big in ww1.
Originally, you did not really buy bullets from the store…..back in the old single loading blackpowder days you bought a mold and some lead and cast your own bullets, so it was convenient to just use the measurement of the bullet. In modern times, it’s not just the bullet but the casing that has to match as well and nearly everyone buys ammunition from retail establishments so we have just had to agree on what to call different types of bullets which is why you get weirdo situations like .45-70 rifle rounds and .45 pistol bullets being wildly different and .223 and 5.56 being nearly but not entirely compatible with each other, and some bullets are say 7mm rifle rounds, but another similar sized bullet but different sized-casing might be 7.56 for example. It’s all over the place and just depends on agreed upon naming conventions in the gun community, and end users and governments…….and that gets really wonky sometimes.
Its just 8.82 gets rounded up to 9. It its entirely in line with the “land diameter X case length, round up/down” naming convention thats been in use for over a century.
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