9mm ammo in Rockville in 2007. (James M. Thresher/The Washington Post)

I know Colbert I. King was using hyperbole in his Feb. 13 op-ed about the large number of guns in the District, “The District in the grip of guns,” but the .38, .357, .380 auto and 9mm ammunition are all the same caliber. (Caliber is the size of the projectile, or bullet.) The different names are for marketing reasons or because of where the cartridge was developed.

The .38 is 0.38 of an inch; Europe uses the metric system, so 9mm. In Germany the .380 auto is called the 9mm Kurz (short). It could very well be that the 9mm cartridge is the round most often used in crimes in the District because it is the cartridge most often used in semiautomatic handguns, or it could very well be that when all you have is a bullet hole and projectile (without the weapon that fired it or spent casings), the Bureau of Alcohol, Tobacco, Firearms and Explosives defaults to categorizing them as “9mm class.” The hole is the same size regardless of which of the rounds made it.

John J. Meng,

Rehoboth Beach, Del.