Firearms Stack Exchange Archive

Why are .30 and .300 caliber cartridges specified with extra zeros?

• posted by: Bill Nace on 2012-02-21
• tagged: ammunition, terminology
• score: 5

Mathematically, .30 and .300 caliber (like .300 Whisper or .300 Win Mag) are equivalent and both are equal to .3 caliber. Are the extra zeros there to give more precision (i.e. more significant digits)? Or are they there just to make it easier to say?

Some other reason?

Answer 1077

• posted by: Gene Temple on 2012-02-21
• score: 5

Cartridge names are pretty random and modern cartridges are usually named by their designer, so it’s whatever they’d like. However, there is the notion of “caliber” which is the diameter of the bullet in hundredths of an inch. e.g. “30 caliber” as an explanation for why we don’t see 0.3 Winchester.

The .30 Carbine, .300 Whisper, .300 Win Mag, .30-06, and .308 Winchester (and many more) all take the same caliber bullet (0.308” diameter), so the apparent “precision” is misleading.

Answer 1094

• posted by: Daniel Chisholm on 2012-02-24
• score: 1

Yup, what Gene said.

Other cartridges that use .308” diameter bullets:

• 303 Savage
• 7.5mm Swiss
• .30-30 Winchester
• .307 Winchester (its a rimmed case version of the .308Win)

And some cartridges whose names might make you think that they use .308” bullets but they don’t:

• 7.62x39 (it uses a .311” bullet)
• .303 British (it’s called “303” because its bore diameter is .303”, but its groove diameter is .312” and that’s why it uses a .312” bullet.)

You’ll know you’re starting to become a cartridge geek when you know the whys and wherefores of all of these true statements:

• a .303 British has a larger diameter bullet than a .308 Winchester
• a .308 Win is more powerful than a .303 Brit
• a .303 Brit is a bigger case than a .308 Win

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