Been using 777 in everything from .22, .44, .45, .50, .54 and 12 gauge. Never had any issues. It's no easier to clean up than anything else. But it is easy to clean up with HOT water.
Seems to work well with cap and ball revolvers, 209 primed rifles and shotguns and also in side lock rifles. The oldest of these guns were 70's vintage.
I've filled the chambers of an ROA as full as possible with 777 under a .457 round ball, no problems. Other than that I've stuck to the 15% reduction by volume.
Local stores have only three 'black' powders- 777, Pyrodex and 209. Real Black isn't happening here. Its what I can get and although not historically correct, it works.