Just for the record...
Unique and the .41 and cast 210 SWCs were divinely ordained. I'm convinced of it and I'm stickin' to it.
7.5 grains duplicates the old "Police" load offered by Winchester and Remington...which had an advertised velocity of 970 fps. Most lots didn't quite make that, though, and averaged around 900-30 give or take. Some few didn't break 900. From my Model 58, 7.5 grains is good for 950 and will flirt with a thousand in the 4.625-inch Blackhawk.
Stepping up to 8 grains puts it solidly into the "Grand" category from most 4-inch barrels.
Accuracy improves a little as well.
8.5 grains is the Holy Grail for Unique and cast bullets and the .41 Magnum. 50-yard accuracy is often astounding, and it's no weak sister in the horsepower department.
1100 fps is attainable in short Blackhawks. There seems to be something about that extra half-grain that hits the pressure curve just right.
Going up another half to 9 grains, and you're starting to get into genuine "magnum" territory. Again, it just seems to hit the pressure curve just right for a decent velocity jump. Bump up to 10 grains, and you've into the point of diminishing returns, and there's really no sense in going above 9 grains. You get more recoil and noise for little power gain.
If more power and velocity is needed...it's time to switch to 2400 and start over. The .41 seems to respond better to 2400 than the "other" two magnums, and rewards the careful handloader with velocities at safe pressures that make me look at the chrono screen and ask: "Are you sure about that?" Then...several more rounds verifies that it wasn't a fluke...and the accuracy is still right there, unlike some calibers and power loads that often start to scatter shots as pressure and velocity go up. I don't know what to make of it, or attribute it to...but the .41 is just nearly as perfect a revolver cartridge as anything I've seen. Good bullet diameter and mass...velocity and power...accuracy...flat trajectory. It's got it all, and a shame that it's been eclipsed by its smaller and bigger cousins, and ignored for the most part. Of course, the upside is that there are more .41 Magnum revolvers for me.
Now for the caveat. 2400 provides a sharp rise in velocities at safe pressures, but when the peak is reached...it can spike quickly and become unsafe with just a half-grain more powder. (Yeah. Ask me how I'd know about that.) When you start to see only small velocity increases with half-grain increments...stop. You've taken it as far as it's gonna go without taking a risk.