so how does one turn a 308 or 7-08 case into a 243

Good neck lube, and run the 308 into a 7mm die first, lube again and into the 243 die. Might have to neck turn after that. And might want to anneal depending on brass.

When going to 7mm, take out the expander ball.

Its that easy. I make .260 Remington brass the same way from .308.

Why not just buy the brass or shoot factory for the brass and not have such a PITA doing the work? I load all 3 and have no desire to go through the hassle of all the forming needed.

pretty good description of the process.....I might add that the length of the case might require substantial trimming after this process...be sure to check and trim the brass to the responsible length.