Why would you even want to do that?
Well I've used commercial sabots, off and on, for over thirty years. I could find numerous sabots commercially, that used bullets in the sabot, but I was having little luck finding sabots for round lead ball.
Well after much searching I found a supplier and the now manufacturing supplier.
Starting using one like this in the mid 70's. I've been using a homemade mix for "greasing" up the cloth patches.
For awhile I thought the plastic patches for round ball were discontinued. Good to see they are on the market.
"Anybody who can stuff a 28 ga plastic wad in a 50 cal rifle with bare hands and a ball starter has my attention."
I lot of people ran into trouble loading the plastic sabot and the ball at the same time. Our practice, started by my mentor, was to load the powder; put in the sabot, ALONE, and push that very easily down the barrel, to the powder, with the ramrod. Then we would take the round ball and drop that down barrel. We would insert the ramrod in the gun and tap the bullet into the sabot. Worked for us. Never had trouble forcing a sabot and a round ball down a slightly fouled barrel. Or breaking the old wooden ramrods.