Probably wouldn't come up in a search, but we talked a lot, years ago, on black powder and smokeless loads with round balls in 12 bores. The same methods would work in a 10.
I used the base cups cut from trap wads to sit under the ball, with card or filler wads taking up the excess space, when using smokeless loads, with another base cup wad, cup down on the powder if smokeless) and if BP loads, just the hard card wads between the plastic cup and the powder.
If you don't have or can't get 10 bore plastic cup wads (Ballistic Products might have them - or some other outfit in the States) you can use hard cards with the centre punched out. A 3/8" punch would do. The idea is to have a wad that will centre the ball in the bore.
Worked for me.