Nomenclature
The name of any given cartridge does not necessarily reflect any cartridge or gun dimension. The name is merely the standardized and accepted moniker. SAAMI (Sporting Arms and Ammunition Manufacturers’ Institute) and the European counterpart (CIP) and members of those organizations specify correct cartridge names. Cartridge names, when correctly presented, never include a naked leading decimal point.
It is a common misnomer to refer to a cartridge as a certain “caliber,” e.g. “30-06 caliber.” The correct full name for this cartridge is .30-'06 Springfield. In sporting arms the only consistent definition of “caliber” is bore diameter. Dozens of unique .30-caliber cartridge types exist.
There is considerable variation in cartridge nomenclature. Names sometimes reflect various characteristics of the cartridge. For example, the .308 Winchester uses a bullet of 308/1000-inch diameter and was standardized by Winchester. Conversely, cartridge names often reflect nothing related to the cartridge in any obvious way. For example, the .218 Bee uses a bullet of 224/1000-inch diameter, fired through a .22-in bore, etc. The 218 and Bee portions of this cartridge name reflect nothing other than the desires of those who standardized that cartridge. Many similar examples exist, for example: .219 Zipper, .221 Fireball, .222 Remington, .256 Winchester, .280 Remington, .307 Winchester, .356 Winchester.
Where two numbers are used in a cartridge name, the second number may reflect a variety of things. Frequently the first number reflects bore diameter (inches or millimeters). The second number reflects case length (in inches or mm). For example, the 7.62×51mm NATO refers to a bore diameter of 7.62 mm and has an overall case length of 51 mm. The commercial version is the .308 Winchester.)
In older black powder cartridges, the second number typically refers to powder charge, in grains. For example, the .50-90 Sharps has a .50-inch bore and used a nominal charge of 90 grains (90.0 grains (5.83 g)) of black powder.
Many such cartridges were designated by a three-number system, e.g., 45-120-3¼ Sharps: 45-caliber bore, 120 grains of (black) powder, 3¼-inch long case. Other times a similar three-number system indicated bore (caliber), charge (grains), and bullet weight (grains). The 45-70-500 Government is an example.
Often, the name reflects the company or individual who standardized it, such as the .30 Newton, or some characteristic important to that person.
The .38 Special actually has a nominal bullet diameter of 0.3570 inches (9.07 mm) (jacketed) or 0.3580 inches (9.09 mm) (lead) while the case has a nominal diameter of 0.3800 inches (9.65 mm),. Hence the name. This is historically logical. The hole drilled through the chambers of .36-caliber cap-and-ball revolvers when converting those to work with cartridges was 0.3800 inches (9.65 mm) and the cartridges made to work in those revolvers was logically named the .38 Colt. The difference in .38 Special bullet diameter and case diameter reflects the thickness of the case mouth (approximately 11/1000-inch per side). The .357 Magnum evolved from the .38 Special. The .357 was named to reflect bullet diameter (in thousandths inch), not case diameter. “Magnum” was used to indicate its longer case and higher operating pressure.
The .30-'06 Springfield round is (nominally) a 0.30 inches (7.6 mm) military round designed at the Springfield arsenal in 1906.
The .303 British is for a bore nominally 303/1000-inch and this chambering was standardized by the British Army.
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