Your results are intersting, Maxiball- while I haven't tried it in the Muzzleloader, I do use it in my Model 71 Mauser that's re-chambered to .450 Alaskan. I bought 10 pounds of it some years ago, and have just gotten around to trying it in the ctg. guns.
: With 76gr.(true weight) of Black MAg 3 and a 500gr. cast bullet, I get 1,500fps. from the 22" barrel. This is MUCH higher velocity than I would expect form a like charge of BP- 1,200fps being closer to what should have come from the screens. BTW - it produces much higher velocity and lower pressure than Pyrodex. How it compares to 777, I don't know as I havne't done that test yet.
: Fouling wise, there is very little and accuracy is splendid - amazing, actually, considering the conditon of the bore. After 50 fire-lapping shots with 400 grit on bullet noses, the bore is starting to shine.
: Blk/MG/3 looks like beach sand.
: The written test I saw showed much higher velocities than any other 'smokeless" black powder replacement with lower presures as well- a perfect result- IF it gives as good accuracy as well. I have never received good accuracy with Pyrodex in the ctg. guns due to large SD's. This stuff appears to be perfct for the BP ctg. gun.
: I tried one shot of it in my .45 Flinter and had a devel of a time getting it to go off. In a muzzleloader, I'd expect it would require a caplock at least or perhaps a 15gr. primer charge of BP first in a flinter. A primer charge in the cap-gun might also be a good idea. As this slows loading time, I wouldn't consider it for the ML gun, but it certainly works well in the BP ctg. gun.