When we left off in our last post, we saw that cartridges like .45-70 and .50-90 were named based on their caliber and the amount of black powder in it (e.g. .45-70 has a bullet of .45 inches in diameter and 70 grains of black powder). We also saw that if two different bullet weights were available for the same cartridge, then a 3 number scheme was used (e.g. .45-70-405 and .45-70-500, where the 405 or 500 indicates the weight of the bullet in grains). We will continue our discussion in this post.
With the invention of newer smokeless powders, cartridges still retained the same two digit naming scheme as before: e.g. the famous .30-30 Winchester rifle, .32-20 Winchester or the .30-40 Krag, which replaced the .45-70 in US military service. As before, the first number indicates the caliber (e.g. 0.30 inches diameter) and the second number indicates the amount of smokeless powder in grains.
After some years, people began to drop the amount of grains and use the year that the cartridge was introduced instead. For instance, the Springfield .30-06 cartridge. This cartridge's diameter is 0.30 inches and it was introduced in 1906 (from which we get 06) and therefore it was named as .30-06. The .30-06 actually replaced the .30-03, which was, predictably, adopted in 1903.
Some years after that, people began to drop the second number altogether and simply name the cartridge after the caliber and the company that introduced it (e.g.) .44 Colt introduced by Colt firearms, .32 S&W invented by Smith and Wesson etc. Sometimes they were named after a specific product (e.g.) .45 ACP where ACP stands for Automatic Colt Pistol. Sometimes they were named after specific attributes (e.g.) .38 Special, .44 Magnum, .577 Express etc., where the words Special, Magnum or Express indicate that these cartridges have extra power.
By the 1950s, people also started to name the first number by the groove diameter of the rifle, rather than the bore diameter of the bullet (at least in America). For instance, .308 Winchester, where the bore diameter is 0.300 inches, but the groove diameter is 0.308 inches.
Over in Europe (except for the UK), people generally use the metric system and name cartridges with two sets of numbers separated by an "x". e.g. 7.62x51, 5.56x45 etc. The first number is the bore diameter of the bullet in millimeters (e.g. 7.62 mm., 5.56 mm. etc.) and the second number is the length of the case in millimeters (e.g. 51 mm., 45 mm. etc.). Note that the first number is the bore diameter, not the groove diameter. Therefore, what we call the .308 Winchester in America actually has a bore diameter of 0.300 inches and a groove diameter of .308 inches and the Europeans take the 0.300 inch measurement and convert that into millimeters (7.62 mm.) and use that in their cartridge nomenclature. This system is generally used in the rest of the world as well (Asia, Africa, South America, Oceania etc.)
The British tend to name their cartridges in American fashion, e.g. .244 H&H Magnum (where H&H stands for Holland and Holland, a famous British firearms firm), .455 Webley (invented by Webley, another British firearms manufacturer) .700 Nitro Express etc. The numbers indicate the diameter of the bullet rather than the groove diameter though.
These are generally the naming schemes in vogue these days, but there are exceptions to the rule. American manufacturers in particular, tend to add names that sound good to consumer ears: e.g. .22 Hornet, .221 Fireball, .224 Rocket etc. Also, there are cartridges such as the .280 Remington (which actually has a bore diameter of 0.277 inches and groove diameter of 0.284 inches) and the .260 Remington (which actually has a bore diameter of 0.256 inches and groove diameter of 0.264 inches). Remington's marketing people decided that customers like numbers that end in zero better, so they named then .280 and .260 instead.
As you can see, these are several ways how cartridges have been named throughout history.