Bore Size Table
| 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" |
Gauge - System of measurement for the internal bore diameter of a smooth-bore firearm based on the diameter of each of that number of spherical lead balls whose total weight is one pound. The internal diameter of a 12 gauge shotgun barrel is therefore equal to the diameter of a lead ball weighing 1/12 pound, which happens to be .729" (Or in British: Bore.)
.410 is not really a gauge, except by convention. It is the actual diameter of the bore in decimal inches.
The Gauge/Bore system is also used to describe the internal barrel diameter of large-bore, 19th century, English, single-shot and double-barrel black powder rifles.
Hallowell & Co. Inc., PO Box 1445, Livingston, MT 59047
Tel: 406 222-4770 Fax: 406 222-4792 Email: morris@hallowellco.com
Abbreviations, Definitions & Opinions Tables Hallowell & Co. Home Page Ordering Information