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Gun bore to gauge conversion table

flintlock and percussion arms

Gauge bore diameter Un-alloyed lead
 

millimeters

inches grams ounces grains
AA 101.60 4.00 6227.20 219.66 96210
A½ 76.20 3.00 2627.10 92.67 40589
0.25 67.34 2.65 1813.14 63.96 28013
0.50 53.45 2.10 906.68 31.98 14008
A 50.80 2.00 778.40 27.46 12026
0.75 46.70 1.84 604.73 21.33 9343
1.0 42.42 1.67 453.24 15.99 7002
B½ 38.10 1.50 328.39 11.58 5074
1.5 37.05 1.46 301.98 10.65 4666
2.0 33.67 1.33 226.64 7.99 3502
3.0 29.41 1.16 151.04 5.33 2334
4.0 26.72 1.05 113.27 4.00 1750
B 25.40 1.00 97.30 3.43 1503
5.0 24.80 0.98 90.57 3.19 1399
6.0 23.35 0.92 75.59 2.67 1168
6.3 23.00 0.91 72.24 2.55 1116
7.0 22.18 0.87 64.79 2.29 1001
8.0 21.21 0.84 56.65 2.00 875
9.0 20.39 0.80 50.33 1.78 778
10 19.69 0.78 45.33 1.60 700
11 19.08 0.75 41.24 1.45 637
12 18.53 0.73 37.78 1.33 584
13 18.04 0.71 34.86 1.23 539
14 17.60 0.69 32.37 1.14 500
16 16.83 0.66 28.31 1.00 437
18 16.19 0.64 25.20 0.89 389
20 15.63 0.62 22.67 0.80 350
22 15.13 0.60 20.56 0.73 318
24 14.70 0.58 18.86 0.67 291
28 13.97 0.55 16.19 0.57 250
32 13.36 0.53 14.16 0.50 219
36 12.85 0.51 12.60 0.44 195
C 12.70 0.50 12.16 0.43 188
40 12.40 0.49 11.32 0.40 175
68 10.41 0.41 6.70 0.24 103

 

Gauge sizes for a given measured bore diameter in inches and millimeters. intended primarily to be a reference tool for those interested in older muzzle loading flintlock and percussion weapons.

The chart assumes a single solid sphere of pure unalloyed lead which is obviously inappropriate for some gauges where several spheres could have been be employed to approximately the same total mass.

It does not take into account conical or unusually shaped projectiles. Neither does it account for a reduction in sphere diameter to accommodate a patch.

Note that the .410 and 23mm are both actual bore sizes, rather than gauges.

This chart seeks to correct inaccuracies noted in other on line tables.