Nick asked in Politics & GovernmentMilitary · 8 years ago

Why both imperial (e.g. .308) and metric (7.62x51mm) are used for calibre measurements?

Hey guys

So I'm just wondering, and I'm no gun nut so sorry if this is a really basic question, why do you sometimes come across one and other times the other? I understand what both measurements mean and that's not what I'm asking, but rather WHY there are two units of measurement? I find metrics are used more with military weapons and imperial with civilian, like when people talk about their own rifles and things, but I'm not sure that's the real difference. If I were to buy ammo, for example, which would I ask the dealer for? Also, when followed by a description such as 'Parabellum' or 'Winchester', is that in order to describe the shape or slight differences or just the manufacturer/brand?

Thanks in advance :) (P.S. yes I'm British (calibRE) if you're wondering)


@wraeth you seem promising :) but anyone else is fine too! ok that makes sense, but maybe you could tell me why see both metric and imperial when it could just be one proper way or the other?

6 Answers

  • Wraeth
    Lv 7
    8 years ago
    Favorite Answer

    Lol trying to explain the differences and the multitudes of information on military and civilian ammo is going to be way to complicated for YA. Essentially yes, when buying ammo, you need to be very specific.

    For instance a .45 caliber ACP is completely different from a .45 caliber Long Colt.

    .22 LR, .22 SS, .22 SH, .22 Mag etc. All nearly identical rounds but different names for specific purposes and weapons.

    Edit: Round are made all over the world. In most cases the military uses metric, and in most foreign countries (ie not the US) use metric for their calibers as well. However, the United States and some nations do not use the metric system, so ammunition manufactured in those nations for civilians generally is in SAE (imperial). Unless that ammunition was manufactured for a foreign weapon that came in metric. IE 8 and 7mm Mauser Rifles, AKs, Mosin Nagants etc.

    It can be very confusing. For instance one of the more popular police pistol rounds in Europe is the 9x17mm or 9mm "Short". In the US this round is known as the .380ACP. Again confusing I know. Essentially you can never go wrong by reading what the ammunition caliber is listed as on your weapon and then purchasing exactly what it says.

    @ Voonie. Did you even READ any of what I wrote about the .22? I was showing how similar caliber names are NOT the same thing. That was the whole POINT of that sentence. Which is why if you will actually bother to READ what I wrote you will see that I said they are all different rounds for different purposes and weapons. Basically stating that just because you read .22, that doesn't mean it goes in your gun.

    Source(s): US Army Scout Military Armorer
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  • Anonymous
    8 years ago

    It all depends on the country of origen. Winchester is a company name, Parabellum is a specific term used for some ammunition, but I'm not totally sure what it means.

    Ammo is confusing, it's true. Most ammo you just kind of have to take case-by-case. .50 AE is very different than .50 BMG. .44 mag is not actually .44 in width. (It was made years ago when diameter was measured by the case, not the bullet itself.)

    Keep googling, keep learning about as many different ammunition types as you can. Eventually it'll start to sort itself out in your head. Good luck!!

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  • 8 years ago

    The Imperial measure is most often applied to sporting arms, while the metric unit is applied to military arms, where precision is a touch more necessary. Note that I said "most often". They're used interchangeably with some frequency, especially in the USA. You'd think that a nation as obsessed with firearms as we Yanks are would be a bit more conscious of precision, but we're just the opposite.

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  • Anonymous
    8 years ago

    specific manufacturers may use different shapes of the cartridge. that's why , Win label.

    the .308 alone simply means the diameter of the bullet.

    the 7.62x51 denotes basic size of the round.

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  • 8 years ago

    Military armorer like hell wraeths answer is so full of horseshit it is hard where to begin. The .22 LR and .22 magnum are completely different rounds the LR is rimfire the magnum centerfire. Lol what a bullshit artist we have here.

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  • Anonymous
    6 years ago

    Hi there,

    you can find a free download of Calibre here

    Check it out.


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