Shotgun gauge conversion

Hi - In the absence of a good caliper does anyone have an accurate formula for converting shotgun gauges - 8,10,12,16,20,28,410 to either metric or inches equivalents?

Thanks

[Robert Fogt]

There is no formula, it is actually just read from a chart. Traditionally there was a method for determining gauge, but that is no longer used.

Gauge/Bore diameter (millimeters)/Bore diameter (inches)
6/23.3/0.92
10/19.7/0.77
12/18.5/0.73
14/17.6/0.69
16/16.8/0.66
20/15.9/0.63
24/14.7/0.58
28/14.0/0.55
32/13.4/0.526

Forgive the poorly formatted chart, as this forum software does not appear to provide tables. The numbers are listed like x/y/z where x is the gauge, y is the bore diameter in mm and z is the bore diameter in inches.

Thanks, I really appreciate the information.

Do you know where I can lay my hands on such a chart???

[Robert Fogt]

That came from the 2005 World Almanac. I do not have any gun books, but they may provide a more complete list.

Thanks - I should have known that given my past profession. I have writter to several of the larger shotgun manufacturers seeking actual posters if they have them.

Thanks again!

correction - written not writter - fingers just aren't working this am!

try this
http://www.unc.edu/~rowlett/units/scales/shotguns.html

I have an old market hunting shotgun with a 1" bore. Does anyone know the gage of this? Roger Miller randcmiller@comcast.net

[Robert Fogt]

That is very close to a 6 gauge, which would have a 0.92 inch bore. About 1/13th inch smaller than 1 inch.