Shotgun gauge conversion

[searunner52]

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.

[searunner52]

Thanks, I really appreciate the information.

[searunner52]

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.

[searunner52]

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

Thanks again!

[searunner52]

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

[junkman1997]

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

[Unregistered]

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.

[Unregistered]

if it is 6 Guage then it will load any size shot in a single collum. That is, in one layer of lead balls. The french did a study years ago, and I think the russians have a military 6 as a result.

[Justem]

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

Thanks, I really appreciate the information. :mad:

[Unregistered]

Just on where (I believe) the original shotgun gauges came from:

Take exactly 1Lb of lead.
Divide it into (say) 12 equally heavy pieces, ie 1/12Lb each
Without removing any metal, roll one of the pieces into a perfect sphere
The diameter of the resulting ball equals the bore of a 12 gauge shotgun.

That's why higher gauge numbers equate to smaller bores. I think this dates from when measuring weight was easier than measuring length.

hth,

Ian

[JohnS]

Just on where (I believe) the original shotgun gauges came from:

Take exactly 1Lb of lead.
Divide it into (say) 12 equally heavy pieces, ie 1/12Lb each
Without removing any metal, roll one of the pieces into a perfect sphere
The diameter of the resulting ball equals the bore of a 12 gauge shotgun.

That's why higher gauge numbers equate to smaller bores. I think this dates from when measuring weight was easier than measuring length.

hth,

Ian

Assuming that is the basis, the density of lead is
11.34 g/cm³ or 0.40968 lb/in³

The volume of a sphere is (pi/6)*d³

if VD = 1 lb/n gauge, then
d³ = (6/pi)*1 lb/(0.40968 lb/in³*N)

d = (4.6618/N)^(1/3) in

that fits the table in post 2 pretty well.

Alternatively, a "N-pounder" cannon would shoot a ball
(4.6618*N)^(1/3) in diameter, a 32-pounder being 5.3" in diameter.

[Unregistered]

Gauge Bore Diameter
1 1.669"
2 1.325"
3 1.157"
4 1.052"
5 .976"
6 .919"
7 .873"
8 .835"
9 .802"
10 .775"
11 .751"
12 .729"
13 .700"
14 .693"
15 .677"
16 .662"
17 .650"
18 .637"
19 .626"
20 .615"
21 .605"
22 .596"
23 .587"
24 .579"
25 .571"
26 .563"
27 .556"
28 .550"
29 .543"
30 .537"
31 .531"
32 .526"
.410 .410"
This should be easier than all the other stuff that has been posted. Hope this helps.

[Unregistered]

Can this Gauge System be Applied to Canister Shells (Basically Cannon sized Shotgun Shells) to where it probably be like .35 Gauge on a 120mm/4.724 Caliber or something like that (I'm not saying that's right)?
Also be Nice if Someone Posted an Equation that can be used to Figure this.

[SAM]

According to wikipedia, that is the formula, not certain whether it can be trusted:
upload.wikimedia.org/math/8/b/3/8b385b0a64dca40778685c157d80ea60.png

[Spraynpray]

The actual derivation of shotgun gauge is defined by the number of balls of lead of that diameter it takes to weigh one pound, so 12 gauge (0.729") means it takes 12 balls of lead of that diameter to weigh exactly 1lb. Smaller the guage, smaller the diameter, larger the number to weigh one pound.

For more info on diameters see wiki under shotgun gauge.

Hope that helps.