The original claim for short fat cartridges being more efficient was based on the clam that the Primer flame would ignite a greater percentage of the powder. True or not I do not know. What I do know is that if this is true then different powders will most likely be required. Probably slower powders for the same calibre and bullet.

I know one bloke who is getting damn near 358 Norma Mag velocities out of his 35 Whelen using a new powder. I do know that long throating a chamber and seating the bullets out a bit does increase the Muzzle Velocity. Roy Weatherby knew a thing or two.