Suba, I used to shoot loads like that when I was younger and my wrists were stronger.
I used H110, there's few, if any, 400 gr. loads that you could call reduced loads. I used a 420 gr. cast sized to .452, .45C cases, H110, cci 350, FA 71/2" .454 for 1358 fps. That same load out of a 10" contender .45C was 1496fps and recoil was way more than I wanted
even then. But for you only wanting 1000 fps, I'd suggest starting with the same load you use for the 360, you might have to tweak it a little if you want it exactly 1000 but it's gonna be close. Mostly now I shoot 320 fpgc at 1350 from a 6" FA .54 and the same load at 1250fps
from a 6" Ruger BHK.
H08