Steve, from memory the .300 Savage was based upon the 30-06, and when the military went looking for a shortened round to replace the 30-06 they looked hard at the .300 Savage but because the shoulder angle was too severe to cycle well in automatic weapons the raised the shouler something like 17 degrees (this is from memory so it is probably off) and adjusted the length slightly and called in the 7.62 X 51 NATO. Within a short time it was loaded commercially as the .308 Winchester.
The government wanted to save weight and reduce recoil.
