Don't know if anyone is still reading this thread, but after looking it over, I loaded up five rounds using a .3cc Lee scoop, which, according to my RCBS 10-10 scale, gives 1.3 grains of Trail Boss. I based my "data" on the fact that this is the recommended scoop for at least two other powders (Green Dot and 700X) with this cartridge and a 158 gr LSWC. The primary mission in developing loads for this powder seems to be not compressing it, which does not happen with this combination. As this powder is designed to be bulky, I reasoned that if I did not compress it, I could not get enough into the case to cause any problems. I used Acme bullets sized at .358. Test gun was a Colt Police Positive. Old Fuff is correct, Colt used the same bore and throat specifications as for .38/.357 revolvers, so in this revolver, .357-.358 is the "correct" bullet diameter (your mileage may vary). Shooting this load was a pleasant experience, very little recoil, very little noise, and acceptable accuracy for a 4-inch revolver with rudimentary sights fired by a 58-year-old man in dim morning light. The box of Cheerios did not survive. If I am permitted by She Who Makes My Schedule, I will do some more serious testing this weekend.
Dale