M-1 Garand: 19 rounds to the pound
Might want to check that. Both shot the same ammo, but the Garand ammo was packed eight to an en bloc clip, which added weight. The Springfield had a stripper clip at most.
WWI .30/06 round was 174 grains bullet.
WWII .30/06 round was 150 grains bullet.
There were two attempts to convert to 150 grain bullet, the first failed, because many officers and men recalled the usefulness of long range machine gun fire. The second one failed, as there were fewer old officers and men around, and as the fact that the 174 grain round overshot ranges was more important. In WWI heavy machine gun training was mostly conducted in Europe.