Seeing this video reminds me of observations I've had with various bullet/sabot combinations. I have some bullets that will slide into the sabot very easy, if I turn the sabot upside down it will fall out. I have some bullets that will start to spread the petals and "hangs up" prior to bottoming out in the sabot . I've always thought the later, although much harder to load, forces the sabot walls into the grooves more than something that slides down easier.
I would think a tighter fitting, harder to load bullet/sabot combination would be more accurate than a loosey goosey one - I could be wrong.