Decimal points belong in written expressions of a gun's caliber.
Since all the guns we own have bores of less than one inch in diameter, every time we type a caliber online it is correct to use the decimal point. That shows that the "caliber" being described is actually a fraction of an inch.
.45 caliber is nominally 45/100 of an inch.
.30 caliber means the hole in the bore, before any rifling grooves are cut into it, was drilled with a 0.30" bit.
A 9mm is not really a "caliber" although we may call it that in common usage, instead of saying "9 mm bore cartridge" or something weird like that. We might say we carried three "caliber" guns to the range today-- a .38, a 9mm and a .40. We might say our newest concealed carry gun has a "caliber" of 9mm. Thats no big deal. I'm not criticizing that. It's a technicality.
What I will criticize is sticking a decimal point in front of a millimeter-designated metric cartridge. A millimeter is a tiny thing, like the thickness of a grain of Uncle Ben's rice. All the guns and bullets we talk about here online are GREATER than one full millimeter. In fact they'll all be over 4 mm, as the smallest-bore cartridges I know of are the .17 calibers, and they're nominally 4.5 mm.
Therefore, don't call your 9 x 19 mm pistol a ".9 mm" unless you want to look like an ignoramus who doesn't know the difference between an inch and a millimeter, or has no idea what that little dot that looks like a period means when used with numbers.
(If you've forgotten 3rd grade math and need a reminder what a decimal point is, click this link to watch a helpful video:
https://www.khanacademy.org/math/ar...iew-decimals-intro/v/introduction-to-decimals
or this one:
https://www.khanacademy.org/math/ar...ith-review-decimals-intro/v/decimals-as-words
Since all the guns we own have bores of less than one inch in diameter, every time we type a caliber online it is correct to use the decimal point. That shows that the "caliber" being described is actually a fraction of an inch.
.45 caliber is nominally 45/100 of an inch.
.30 caliber means the hole in the bore, before any rifling grooves are cut into it, was drilled with a 0.30" bit.
A 9mm is not really a "caliber" although we may call it that in common usage, instead of saying "9 mm bore cartridge" or something weird like that. We might say we carried three "caliber" guns to the range today-- a .38, a 9mm and a .40. We might say our newest concealed carry gun has a "caliber" of 9mm. Thats no big deal. I'm not criticizing that. It's a technicality.
What I will criticize is sticking a decimal point in front of a millimeter-designated metric cartridge. A millimeter is a tiny thing, like the thickness of a grain of Uncle Ben's rice. All the guns and bullets we talk about here online are GREATER than one full millimeter. In fact they'll all be over 4 mm, as the smallest-bore cartridges I know of are the .17 calibers, and they're nominally 4.5 mm.
Therefore, don't call your 9 x 19 mm pistol a ".9 mm" unless you want to look like an ignoramus who doesn't know the difference between an inch and a millimeter, or has no idea what that little dot that looks like a period means when used with numbers.
(If you've forgotten 3rd grade math and need a reminder what a decimal point is, click this link to watch a helpful video:
https://www.khanacademy.org/math/ar...iew-decimals-intro/v/introduction-to-decimals
or this one:
https://www.khanacademy.org/math/ar...ith-review-decimals-intro/v/decimals-as-words