These numeric designations represent two distinct centerfire rifle cartridges. The first number, 7.62, refers to the bullet diameter in millimeters. The second number signifies the cartridge case length, also in millimeters 51mm and 63mm respectively. This fundamental difference in case length dictates variations in powder capacity, overall cartridge length, and ultimately, ballistic performance.
The choice between these cartridges has significant implications for firearm design, function, and intended application. The shorter, lighter .308 Winchester (7.62x51mm) cartridge, developed after World War II, offers advantages in terms of magazine capacity and weapon maneuverability. The older .30-06 Springfield (7.62x63mm), adopted by the U.S. military in the early 20th century, historically provided a longer effective range and greater stopping power. These differing characteristics influenced their respective adoption by various militaries and civilian users worldwide. Understanding the historical development and performance characteristics of each cartridge is crucial for informed decision-making regarding firearm selection and ammunition procurement.