Gauge is a term used to identify the inner diameter of a shotgun bore and the size of the shotshell designed for that bore.
Gauge is determined from the weight of a solid sphere of lead that will fit the bore of the firearm and is expressed as the multiplicative inverse of the sphere’s weight as a fraction of a pound, e.g., a one-twelfth pound lead ball fits a 12-gauge bore. Thus there are twelve 12-gauge balls per pound, etc.1
Cartridges of the World, 16th Edition
Cartridges of the World, 16th Edition is packed with over 688 pages of concise information and data on old, new and currently manufactured ammo. Heavily illustrated with more than 1,500 photos, this book is the ultimate guide for gun owners interested in current and historical ammunition for handguns, rifles and shotguns.
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- Barnes, Frank C.; Woodard, W. Todd (2016). Cartridges of the world : a complete and illustrated reference for more than 1500 cartridges (15th ed.). Krause Publications. p. 629. ISBN 1440246424. OCLC 934886116