[tpcollins]

I dont want to start a pi$$ing contst but has this been observed by some type of see-thru barrel apparatus with a slow motion camera or is this from a physics professor's calculations on a blackboard?

You can put a patch over a jag on a cleaning rod up against the breech plug, fire a 209 primer, and the cleaning rod will move quite a ways back up the barrel. To me that seems like a lot of pressure that wants to go somewhere in a hurry, but if Mr Sabot doesn't move until after his skirt gets spread into the rifling first, then that's really good information to know.