mm to cal
by choogh on 08/13/03 at 21:33:43

Some firearm barrels are measured as metric while others are measured as caliber (calibre if you are English) and others (Shotguns) in guages.  So, a 40cal is how many mm?  A 12 guage is how many cal, mm? etc
Is this a worthy topic?

Re: mm to cal
by Robert Fogt on 08/14/03 at 04:19:05

Yes thats a great topic. I have been asked about it many times and it is on my to-do list.  I have done some research on the subject, but have not created an automated conversion for it yet.

The following came from  Russ Rowlett and the University of North Carolina at Chapel Hill.

Originally, the gauge of a shotgun was the number of lead balls, each of a size just fitting inside the barrel, that were required to make up a pound. In other words, if a lead ball weighing 1/12 pound just fit in the barrel of a shotgun, then it was a 12-gauge shotgun. Though today, the diameter is measured and the gauge is determinded from a chart.

[table]
[tr]
[td]Gauge - [/td]
[td]mm diameter - [/td]
[td]in. diameter[/td]
[/tr]
[tr]
[td]6[/td]
[td]23.3[/td]
[td]0.92[/td]
[/tr]
[tr]
[td]10[/td]
[td]19.7[/td]
[td]0.77[/td]
[/tr]
[tr]
[td]12[/td]
[td]18.5[/td]
[td]0.73[/td]
[/tr]
[tr]
[td]14[/td]
[td]17.6[/td]
[td]0.69[/td]
[/tr]
[tr]
[td]16[/td]
[td]16.8[/td]
[td]0.66[/td]
[/tr]
[tr]
[td]20[/td]
[td]15.9[/td]
[td]0.63[/td]
[/tr]
[tr]
[td]24[/td]
[td]14.7[/td]
[td]0.58[/td]
[/tr]
[tr]
[td]28[/td]
[td]14.0[/td]
[td]0.55[/td]
[/tr]
[tr]
[td]32[/td]
[td]13.4[/td]
[td]0.526[/td]
[/tr]
[/table]

The caliber is the inside diameter of a gun barrel stated directly in inches. A .22 caliber gun has a bore of 0.22 inches.

Not to be confused with the caliber stated for guns on warships, which are a ratio.

Re: mm to cal
by choogh on 08/14/03 at 07:04:32

Oh Wow!   What a wonderful response time.  Thank you for the information.

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