Maximum pressure is maximum pressure in any reasonable length of barrel, and max. loads developed in a 24" barrel should not be exceeded in a 22 inch barrel. Powders that give maximum velocity in a 24" barrel will almost certainly produce the maximum velocity possible in a 22" barrel. There will be a small velocity loss due to the shorter barrel, but it will be irrelevant to the actual performance of the load on game.
This is quite true, in practical usage.
You can get surprises, though.
I at one time owned two #1 Ruger single shot rifles in 30-06.
One had a 26" barrel [#1B], the other a 22" tube [#1AB]
With exactly the same load, [5X grains of IMR 4831] the 22" barrel was consistently faster by 80fps than was the 26" barrel.
It is hard to explain this phenomenon, but it does occur.
Before anyone says that pressures must have been different
in these rifles, adding 2 grains of powder to either rifle's load
showed similar high pressure indicators, so it becomes somewhat
of a mystery.
FWIW, you should try Reloder 17 in that 243.
Regards, Eagleye.