Forums / Gun Discussion / Where do the caliber numbers come from?

7 years 30 weeks ago, 7:45 AM

Tyrnt

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I know it is the measurement of the barrel from land to land, but one could say 9mm for a 9 millimeter and "40 caliber" for a .40. My question is what is .40 or .45 of? an inch? because if I remember correctly a .40 is 10mm right? I took a gun permit class yesterday and my instructor didn't know what the ".40" is a measurement of.

Thank you

6 years 43 weeks ago, 1:03 PM

bulletbob

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caliber is the decimal equivalent of an inch. thus .25 caliber is 1/4 inch in diameter amd .50 caliber is 1/2 inch in diameter.

6 years 41 weeks ago, 8:56 PM

Infidel

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True........but

What BulletBob says is true as far as it goes, but the expression of caliber does not always make sense and that is just the way we do things in this country. For example; .38 caliber is not thirty eight hundreths of an inch as you might think. it is actually .357 of an inch. There are other calibers that don't express their exact measurements also. If you are interested in the caliber dimensions a good place to learn would be a reloading manual, which gives the dimensions of each caliber. Hope this helps to answer your question.

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6 years 21 weeks ago, 3:17 AM

bob fairlane

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But its starting to be more and more appealing, esp when you go to work on a car or something and have to figure out whether every damn screw is Metric or SAE.

6 years 21 weeks ago, 9:24 AM

samD

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Metrics

I live right off of Hiway 19 in Arizona. It connects Tucson to Nogales, Sonora mexico. It is, I am told, the only Highway in the US in Metric. All the distances are in kilometers. I guess so the 1% +/- of the illegals who go home, will know how far it is...
samD

6 years 19 weeks ago, 3:34 PM

Clarkey

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And then you get the weird ones like .30-06 and 22-250, .30 being the bullet and the 06 being the year it was introduced and the 22-250 is saying its a .22 bullet in a case from a .250 necked down.

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