especially as both were flat base rounds (the ballistic penalty for that starts kicking in when they go transsonic which for those would probably be around 250m).
Only the Germans issued cartridges featuring boat tails during WWI, and other nations were slow to adopt that to their spitzer designs.
The .276 Pederson had a 125 grain boat-tailed bullet, but this was 'killed' by MacArthur in 1932
The US 1926 30-06 M1 had a 174 grain boat tail, but besides making the new M1 Garand test rifles break, and was long ranged enough to be a problem at Army shooting ranges.
So around a billion of those rounds were allocated for USN use in Machine Guns, and a new M2 Ball of 1936, with a 150gr flat base bullet and different powder, basically recreated the old M1906 30-06 round that was slightly higher MV, but more friendly to the Garand gas trap system was greenlighted.
In October 1939, after around 50,000 M1 Rifles had been made, the decision to goto a standard gas system with a port drilled into the barrel was decided.
IMO, the M2 cartridge was an unneeded bandaid to get the original M1 to work properly. As far as I've been able to discover, the Johnson Rifle worked the same with either Round