This has been covered in spades on all the BP forums (including this one) over the years. If it's been said once, it's been said a thousand times, but just in case:
NO AMOUNT OF SMOKELESS POWDER CAN BE CONSIDERED SAFE IN A BLACK POWDER REVOLVER, WITH THE EXCEPTION OF TRAIL BOSS IN CARTRIDGE CONVERSIONS!
Yes, some folks have done it, but sooner or later their luck will run out and they will wind up with a face full of shrapnel, or worse.
Cartridge conversion cylinders for BP firearms are made of smokeless quality steel that can withstand smokeless pressures while BP cylinders are not designed nor proofed for these types of pressures!
Thanks for posting, Ted. It can't be repeated too often. DON'T DO IT!