David,

8.0 of 231 in a Magnum case is Clint Smith's everyday .44 Magnum load and gives 975-1000 fps in a 4" with a 250 grain cast bullet. I've never gone above 6.0 grains in the Special case and like HoosierMike said, it's a good load. You're looking for a full power load in a Special case, so I'd recommend the Skeeter load (7.5 Unique) or one that's looking even better these days that Brian Pearce recommends, which is 8.0 grains of Power Pistol. It gives a little more velocity than the Skeeter load at standard pressures. I would be a little cautious of trying to get 231/HP38 to give the velocities you're seeking in the short case, because I think pressures would be much higher than you want.