I have a .243 Ackley IMP. Mine isn't what you would find here on Longrangehunting.com Mine is actually a Semi Custom Ruger M77 MKII that has been rechambered and fully accurized. It is a lightweight deer and Coyote rifle meant for my boys for hunting and the occasional Coyote by me. It is very accurate for a light weight rifle.
I shoot 100g Sierra Gamekings and out of a 22" bbl and I'm getting the same velocity out of it that I get out of my .26" bbl rem 700 VLS using 100g Bullets.
I use H414 powder and magnum rifle primers Velocity is just around 3000FPS.
I am using Redding Dies.
As an answer to your question about using .243 Win dies for loading the Ackley. The Answer is no. Chamber dimentions are larger for the Ackley especially in the Shoulder and they won't fit into the dies. The shoulder is quite a bit more forward and would be pushed back making the brass pointless to use.
You need to use the proper dies to load this cartridge.
I have attached this photo as a reference for you. From Right to left the cartridges are: .243 Win, .243 Ackley Imp, 6.5-06 Ackley Imp, .30-06 Ackley Imp, and 7mm STW.
Note the shoulder diffrences between the two .243s