This is the method used by most buffalo runners. Shooting buffalo from horseback with pistols or with muskets/shotguns was a favourite pastime of the military, usually officers.
: Since loading a patched ball was too slow, difficult and time consuming, a mouthfull of balls was used and the rider would spit an undersized ball down onto the powder, hoping the spit would attach the ball to the powder long enough to discharge the shot into the buffalo running alongside. Of course, this lead to many accidents where the barrel burst from being discharged as the ball rolled down the barrel. For your safety, this really shouldn't be done unless there is some way of holding the ball on the powder, as in athin card wad, or, only when pointing the muzzle up at an angle that will allow gravity to hold the ball there, as in Musketman's 4th July adventure - soon to be repeated.
: Personally, I would have used paper ctgs. with blank laods for that along with lube on the outside of the paper ctg. to help keep the excessive fouling soft. I believe I've seen where 120gr. 3F is used in .69 & .75 muskets for the blank charges used in movie making and reinactments. If that isn't enough noise, of course, 150 to 200gr. of 3F could be substituted for the blank charge. I wouldnt' expect pyrodex would make a good blank due to the slowness of it's burn, unconfined. it would also probably need a BP booster.