Understanding the Names of Firearms Cartridges

The 30-06 Springfield
Features of a 30-06 Springfield cartridge. The bullet is the black thing with the red polymer tip. Russ Chastain

Firearms are generally categorized by the size of the ammunition cartridges they use, but the naming conventions can be confusing, and not even experienced shooters can always tell you what "30-06," "375 H & H Magnum," "270 Winchester," etc. mean. 

The fact is, there's really not much consistency in the way that ammo is named. Generally speaking, the numbers associated with ammunition refers to the diameter of the metal bullet--a .22 is .22 inches in diameter, a .45 is .45 inches in diameter. But discussion of caliber is sometimes misleading because a cartridge's name doesn't always accurately represent actual bullet diameter. That is why it is more accurate to omit the decimal from cartridge names; the actual numbers simply don't always represent reality. Here are some details for the most popular ammunition types: 

  • The 30-06 stands for the caliber (.30, or more accurately, .308 inch) and the year (1906) that it was adopted as the standard US military rifle cartridge.
  • The 270 Winchester's name is made of the approximate bullet diameter (it's actually .277") and the manufacturer who standardized the round and brought it into commercial use.
  • The 375 H&H Magnum is comprised of bullet diameter (.375"), manufacturer's name (the famed British firm Holland & Holland), and a word that has long been used for marketing ammunition: Magnum, meaning that is is somewhat larger than other ammunition in the same caliber. 
  • The 220 Swift combines a round number that's somewhat close to bullet diameter (.224") with the word "swift," which is quite appropriate considering that is it an extremely fast cartridge. Although introduced by Winchester, that company chose not to include the company name in the cartridge's moniker.
  • The 45-70 Government was thus named because it was officially adopted for government use, its bullet diameter (.458"), and its original loading of 70 grains of black powder. At one time, this was a fairly standard way of naming cartridges. . . until smokeless powder was developed.
  • The 30-30 Winchester is a fairly unique creature. The first 30 refers to bullet diameter (.308"), while the second thirty refers to a theoretical 30 grains of black powder. It's theoretical because the 30-30 never was loaded commercially with black powder; Winchester kept up the previous cartridge-naming convention simply because that's what shooters were used to, and the smokeless load was more-or-less equal to 30 grains of black powder.
  • The 45 ACP combines bullet diameter (.452") with initials for its original firearm, which was the Model 1911 Automatic Colt Pistol.

If you think the info above is confusing, try this:

  • A 38 Special bullet is actually .357" diameter.
  • The 44 Remington Magnum shoots a bullet that may vary from .429" to .431" diameter.

A discussion of all these vagaries could go on and on. While generally the names and numbers associated with cartridges refer loosely to bullet diameter or caliber, the names are often inaccurate when it comes to describing the dimensions of the actual cartridge.