243 75HP Powder

IMR 4350, H4350 and RL 17 should work. I have used IMR 4350 for the .243 and the 6mm Remington. Drops yotes lightning fast and speed is pretty impressive.
Another good choice is RL-15. Only messed with it once in my nephews Savage, but it was very accurate. Lots of people like Varget and H4350