The following powders give you best potential combination of velocity/fill/burn w/ the .243Win/75gr A-Max for max working (55,000psi) pressure in a 24" barrel:
3,418 Norma MRP
3,412 Alliant Reloder-25
3,347 Ramshot Hunter
3,339 Accurate 4350
3,321 IMR 4831
3,311 Hodgdon Hybrid 100V
3,291 Accurate 3100
YMMV of course.