Hodgdon's website recommends a maximum of 25 grains of 777 with the 1858 Remington and 1860 Colt, both in .44 caliber. The suggested starting load is 20 grains.
For the .36 caliber, start with 15 grains. The maximum is 20 grains.
These are with steel-framed revolvefrs only. Hodgdon does not recommend the use of 777 in brass-framed revolvers.
I've been shooting cap and ball revolvers since about 1971. I've tried about every substitute I could get my hands on, but always return to black powder. It has proven to be the most accurate and not so finicky as the substitutes.
If you can't find black powder, get Pyrodex, Grade P. It's not as accurate as black powder, but it will allow you to shoot your revolver. It's also allowable in brass-framed revolvers.
I would pass on Hodgdon 777. I haven't found it very accurate.