NO, NO, NO! TERRIBLY DANGEROUS. Tin Star is half-again more dense than Trail Boss. You could double pressure doing that. Plus, that 70-100% formula is for using Trail Boss with jacketed bullets in high power rifle cartridges designed to operate at way above 44 Special pressures. Never presume to carry rifle load densities over to handgun cartridges without checking with the manufacturer. Never presume data that is good for one powder is good for another without checking with the manufacturer.
Vihtavuori has CAS data for Tin Star in the .44 Special. The bullet is heavier than yours at 248 grains, but it shows maximum .44 Special pressure is reached at about 55% fill of the space under the bullet. The 200-grain will be similar. Probably about 7.5 grains, but stick with the 6.3 grain published maximum for the 248-grain bullet unless you know it isn't working for you and you know how to read revolver pressure signs to work up to 7.5 grains.
QuickLOAD confirms the pressures. At 70% fill, you would be in proof load range for the .44 Special. At 100% you would exceed .44 Magnum pressures, running at around 40,000 psi. At 55% it lands right in the middle of the high-pressure range. It looks like it predicts this particular powder well.
