Re: 243AI vs 243
There are thre ways I know to form AI brass. Easiest is to load a mid level load in the parent case with a heavier bullet, and shoot it. You can load these on your AI dies. Second way is to use a small amount of pistol powder such as Unique, then fill the case with unique, and cap with some toilet paper and paraffin wax, point up and shoot. Probably the best way to save barrel life is to get some hydraulic forming dies, where the case is filled with oil and then you hit it with a hammer, forcing the case to stretch under the pressure so it fills the die.
The 6mm AI is a heck of a cartridge and you can neck down high quality 7x57 brass if you feel that it is necessary.