There was a good article in the last Handloader magazine about black powder revolver ammunition by Mike Venturino. He has three main recommendations:
Use a black powder bullet lube like SPG.
Use magnum primers.
Load through a drop tube to settle the powder in the case.
You probably cannot get 21 grains in thick modern brass, just use enough to be sure it is at least a little compressed by the bullet.
If all that sounds like too much trouble, one of the fake powders will give you something of the experience. I shot some .44 Specials and .44-40s with 777 and they were smoky, kicked, and heated up the guns fast. Didn't smell right, though. It did not require SPG lube, ordinary hard wax is ok, and even though the guns were sooty, they cleaned up easier than with real black.
On the other hand, it left the brass just nasty; it had to be washed, dried, and tumbled to clean up. If I were loading 777 in .38 special I would just use some well worn brass and ditch it when done.
