The current issue of 'Handloader' magazine has an article by John Barsness on big bore Brit rifles. He discusses his experience with smokeless in the .450/.400 using 5744:
"The boys at Western Powders have a formula for finding a starting load with 5744: 1) fill a case with 5744 to about where the base of a seated bullet would be; 2) weight the powder and 3) use 40% of that powder charge.
The formula resulted in a charge of 23 grs, producing a muzzle velocity of around 1,000 fps. Since 1,400 fps was the goal, I divided 1,400 by 1,000 and multiplied 23 by the result (1.4), a technique that can be used with any single-base smokeless powder. The resulting charge of 32 grs matched the velocity of the black powder load with slightly better accuracy. The only problem was that the 5744 load shot about 10" higher at 100 yds."
If you have any issues with this information, spare me your invective. Contact the magazine. I'm just messenger.
I found the formula I use with 5744 in 45-70 and 50-70 in an article by Ross Seyfried - 40% of the nominal BP charge. That extrapolates to 28 grs. I've upped this to 30 grs and got no benefit accuracy wise, just a tad more recoil. Unlike Barsness's experience, these 50-70 loads shoot into the same group at 50 and 100 yds as my BP loads.