So are these slower powders produce less pressure but same velocity ?
Not exactly, they are doing other things for you such as changing the location/time of the pressure curve peak and altering the recoil impulse.
I don’t have apples to apples comparisons of jacketed bullet load data with pressure information.
I do have quite a bit of apples to apples cast bullet pressure data. Here is some stuff for the Lyman 452424 255-grain bullet fired from a 7” pressure barrel. I looked for approximately equal pressure to give you an idea of velocity difference between the powders.
8.0 grains of Alliant Bullseye ahead of the 255-grain 452424 produces 24,000 CUP for 1,021 fps.
10.5 grains of Alliant Unique ahead of the 255-grain 452424 produces 24,800 CUP for 1,050 fps.
12.0 grains of Alliant 800X ahead of the 255-grain 452424 produces 24,800 CUP for 1,139 fps
24.0 grains of IMR 4227 ahead of the 255-grain 452424 produces 24,400 CUP for 1,192 fps.
18,5 grains of Alliant 2400 ahead of the 255-grain 452424 produces 25,100 CUP for 1,266 fps.