Hodgdon shows a max load for the 240 LSWC in 44 special using HP38/W231:
Max: 5.2 grains, 858 fps at 13,200 CUP OAL 1.450"
Speer 14 shows as max for 240/44 special with W231:
Max: 5.7 grains, 796 fps from a 3" revolver with pressure less than SAMMI max of 15,000 psi, OAL 1.475.
Hornady Handbook, Sixth Edition shows the 240 and 231:
5.8 grains, 750 fps in 3" revolver barrel.
IF the loads will only
be used in a Magnum revolver, one could safely work up from there, but W231/HP38 wouldn't be my first choice. A medium powder like Unique, Power Pistol, Universal, or HS6 would get the velocity you're looking for with less pressure. The old standby Skeeter Skelton was 7.5 grains of Unique under a 250 grain SWC for 900-950 fps and approx 20,000 psi....+p but controllable in an N frame Smith.
Some good reading here: .44 SPECIAL HANDLOADS: Too Good To Be Forgotten | Guns Magazine | Find Articles at BNET