The 150 gr. flat based bullet goes back to WW1 time frame. During the 1920's the military decided that they needed a heavier bullet for use in the machineguns as was the thinking in Europe at that time. So they came out with the Bullet M1. 173 grs. Then along comes Garand and his new rifle which the military likes. But it's in 7mm and not 30-06 which Douglas MacArthur didn't like so he had the rifle redesigned for use with the 30-06. But it did not do well with the heavier bullet as the pressure curve was wrong so they went back to the 150 gr. flat base and IMR 4895 became the powder for the 30-06. This became the M2 round that became the standard for WW2 and beyond.