358WCF,
Pushing Ackley Improved cartridges "hard" is the primary reason they supposedly get significantly more velocity--and always has been. Only a few Ackley Improved rounds get 100 fps more muzzle velocity when loaded to the same pressure--and those are older cartridges with far more body taper than the .338-06, such as the .250 Savage. In most cartridges you can get within 50 fps of the same muzzle velocity by pushing them hard.
I have fooled with a bunch of Ackley (and other "improved") rounds, and so far the only significant difference I've found is the near elimination of case-stretch--which saves a lot of time in reloading hundreds of varmint rounds, but not much in big game cartridges. That said, a lot of recent varmint rounds have a sharp enough shoulder to result in essentially the same thing.
But whatever.....
