The 7.62x51 NATO was designed in the early 1950s. It was basically a 30-06 Springfield shortened from 63 mm to 51 mm. The new U.S. creation was called the T-65 cartridge. There where also submitted several other and far more advanced entries then the T-65, but the U.S. used its considerable influence to override all Allied objections in order to have the 7.62x51 NATO cartridge adopted. The T-65 based 7.62x51 NATO remains a NATO standard to this day.
The 7.62x51 NATO has the same case dimension as the 308 Winchester and you can therefore use 308 Winchester reloading data found here.
This text is based on information from “Cartridges of the
World”, Hodgdon reloading manual, the cartridge designer and/or