HERE IN THE UNITED STATES, we cling to the English system of measurement: inches, feet, yards and miles. But you have to admit that there’s simplicity in the metric system: millimeters, centimeters, meters and kilometers. Generally, European bullet diameters are simple, clear and usually expressed in millimeters or half-millimeters, as in 6mm, 6.5mm, 7mm, etc. There are exceptions, but you get the idea. Americans have been more random, seeming to pick bullet diameters out of a hat: .257 inch, .277 inch, .308 inch — none of which make metric sense. In 1925, when the .270 Winchester (bullet diameter .277 inch) was introduced, America already had two good metric calibers: 6.5mm (caliber .264) and 7mm (caliber .284). Sandwiched between them, the .270 offered very little. But it was the Roaring Twenties,…
