What causes sabot problems/inaccuracy. Some pictures will help.
First 2 shows a skinny post that pushes on a cushion or sabot
bottom and it can bend or deflect which if that way when exiting
barrel can start sabot or slug crooked.

And more important item that causes a lack of accuracy is if the
base of discarding sabot tapers or steps down so that it isn't real
tight as it leaves bore, which can allow it to be cocked.
On the left is our sabot which has base right and other brand
which tapers a bit. Easy to see.

Next is a ball and slug load in 2 of our sabots. A 285gr .575" ball
flattened, put in the bottom and a 400gr Minie above, two different
styles of Minies.

Here is couple 16ga discarding sabots I made from the undersize
12ga grey ones. Didn't have to take off much. Much better use
for them. I made them after Paul in Alaska asked about
where to find 16ga ones, to see what they looked like.
They still use 50cal slug.. Ed