http://old.municion.org/semi/32.htm

1 Pound / gauge = weight of lead sphere Diameter of bore is then measured
gauge pounds mm inches
0.25 4 67.34 2.651
0.5 2 53.45 2.103
0.75 1+1/3 46.70 1.838
1 1 42.42 1.669
1.5 2/3 37.05 1.459
2 1/2 33.67 1.326
3 1/3 29.41 1.158
4 1/4 26.72 1.052
5 1/5 24.80 0.976
6 1/6 23.35 0.919
6.278 1/6.278 23.00 0.906
7 1/7 22.18 0.873
8 1/8 21.21 0.835
9 1/9 20.39 0.803
10 1/10 19.69 0.775
11 1/11 19.07 0.751
12 1/12 18.53 0.729
13 1/13 18.04 0.710
14 1/14 17.60 0.693
15 1/15 17.21 0.677
16 1/16 16.83 0.663
17 1/17 16.50 0.650
18 1/18 16.19 0.637
20 1/20 15.63 0.615
22 1/22 15.13 0.596
24 1/24 14.70 0.579
26 1/26 14.31 0.564
28 1/28 13.97 0.550
32 1/32 13.36 0.526
36 1/36 12.85 0.506
40 1/40 12.40 0.488