Confused!
Well, I presume you are just a bit more confused now, than when you wrote your request for information.
It has been mentioned here, but the truth is a 'one powder fix' will not be optimum for your original three calibres mentioned. A heavily necked down cartridge, like the 243, requires a very slow powder for best performance. With 100 grain bullets an ideal powder is H4831. Better yet, but most likely not obtainable, is Norma 205. Not only will these powders give optimum velocity, but they tend to be very accurate.
4350 is maybe the best all around powder for the 30-06, but in bullets of 200 or 220 grains, again the best is the H4831 class. Years ago Jack O'Connor wrote that he had been playing around with 4831 and 220 grain bullets in the 30-06. He came up with a "wow" load of 4831 that not only gave far more power than factory 220s, but he said it was so accurate that he used all of his supply of 220 bullets, just marveling at their accuracy. I tried his load and my 30-06 never shot more accurate with any load, than it did with the heavy 220 load!
4831 is also about as good in the 30-06 with a 180 bullet, as any other powder. However, fill a 308 case with 4831 and it will probably go "Woof!"
The 308 requires a faster powder. Shortly after the 308 came out, the gun writers of the day, decided H335 was about ideal. They also stated that with the 308 it was hard for a handloader to equal factory ammunition velocities! The factory loads may have been heavier at that time, than they are now.
Yes, one powder will make all three calibres go bang, but won't be best for them.
