However, I do have an Outdoor Life comparative ballistics chart from their "Cyclopedia" that comes from the late 30's. They list the 300 Savage with a muzzle velocity of 2660 fps with 150 grain and the 30-06 as having 2960 fps with the same weight. Of course, this is well after the 300 Savage's introduction. P.O Ackley lists his fastest 150 grain load for 300 Savage as 44 grains of H380 with a ML of 2650 fps. That's from 1962.
Could an enterprising reloader have gotten 2700 fps out of a 300 Savage in the 20's? Possibly, but it was not something I'd have wanted to shoot. Maybe it was Paco Kelly's grandpa. It certainly was not factory ammo.
Yes, the Savage catalogs dropped the muzzle velocity from 2700fps to 2660fps somewhere between 1935 and 1939. Due to better measurements, or slightly reduced load because better pressure measuring showed they were loading hot? Dunno. It's only a 1.5% velocity reduction.
1950: still at 2660fps
1953: cataloged at 2670fps
1972: still at 2670fps
