My favorite powder is IMR 4350 behind a 100 gr bullet. Velocities are slightly over 3100 fps from a 22 inch M70 FWT pre 64.
Factory loads often run about 2900 fps which takes it down in effectiveness a lot.
My loads exceed handbook loads by 2-3 grains so I won't post them. However, when the .243 WCF first came out the writers used 45 gr of 4350.
I have not found any pressure problems. I have worked up loads with 4350 in my rifle that exceeded 3200 fps with 100 gr bullets. I know pressures are high, but do not get hard bolt lift or problems with primers showing too high.
My rifle is a "fast" rifle, and I have never found another that can reach such velocities. I had a friend who had a Sako, and he had difficulty getting over 3000 fps from his rifle.
In my view any powder faster than 4350 can not get the velocities I want in a .243.
I tried H 4831, but the case would not hold enough. Norma 204 is the same burning rate as 4350, and is more dense.
I have not used any of the newest powders, but if you stay with a burning rate of 4350 or slightly slower, if the case will hold it, performance will be fine.
Ecclesiastes 12:13 *¶Let us hear the conclusion of the whole matter: Fear God, and keep his commandments: for this is the whole duty of man.
14 *For God shall bring every work into judgment, with every secret thing, whether it be good, or whether it be evil.