The rule of thumb I use for NON-MAX loads going back and forth between the two (magnum and Special cases) is either add or subtract 10%
Powders like 2400, Win 296, N110, 4227 et al. need not apply.
My lightweight plinking loads with RedDot, Unique and the like +/- %10 seems to keep me around the same pressure.
If it's a load I worked up in 44 mag that shows the slightest ammount of pressure, it get's it's only work up in the smaller case.
But my 6.5gr RedDot under a 200gr RNFP in 44mag brass, shoots just as well with 5.9gr in Special brass.
Same with 7.5gr Unique under a 240gr LSWC, or with 6.7gr in Special brass.