Some years ago when I wanted to develop deer hunting loads for my three screw Ruger Super Blackhawk I started with the standard full power loads in manuals and used by many handloaders for many years. I loaded 22.0 grs of 2400 and 24.0 grs of 296 with CCI 350 mag primers with 250 cast SWCs and 240 gr JHPs. I got higher velocities with 296 than with 2400 so 296 is what I have always used. If you are loading for a quality gun you do not have to "start low and work up very slowly while watching carefully for signs of high pressure". Pressure signs do not occur at magnum pistol pressures and at any loads listed in manuals.