Run a well lubed case into a .260 die. If it crushes the case then run them through a 7-08 die and then the .260 die.

Unless I had a free supply of .308 cases I'd just get some of the great Lapua .260 cases and call it good for a lifetime.

The Chosin Few November to December 1950, Korea.
I'm not one of the Chosin Few but no more remarkable group of Americans ever existed.