If ya wanna go domestic and old school....
work up to 42.5 grains of 4064....that will get you to 3400 fps neighborhoods, depending upon barrel length...
In the 55 to 85 grain bullet arena, IMR 4064 is often over looked... due to being around for a couple 4 decades or more...
and if your 243 won't shoot 4064... then that 243 has accuracy issues to begin with... and even at times, 4064 like SR 4759 will clean that up stretching the old barrel life out...
