You can make .243 Win cases out of 30-06. But you will need to anneal them, and turn the necks afterward because they'll be too thick to work. Now the 6mm-06 is another different animal - same body as a 30-06 but with a 6mm neck. And with it, slow powders, heavy bullets, and fast twist barrels are the deal. They do indeed work well at long ranges, but VLD bullets don't work well much past 3000 fps, and a regular 243 can usually do that anyway.