Understanding Metric and Inch Bore Dimensions
I often have blog readers and consulting clients send me questions about firearms calibers. They are often confused, but this not always their fault. It is a confusing, complex, and often arcane topic. A lot of the facts that you will find are mere trivia, but since safety is an issue–(we mustn’t fire the incorrect ammo in our guns!)–it is important to study. To begin: Metric caliber designations are usually written with an “x” in the middle to distinguish the bore diameter and case length. For example, the 6.5×55 designation tells us that the cartridge uses a 6.5 mm bullet, …