Nice find, Mike.
I'll bet most of those demo rounds are Charge 1 - the bounce on Charge 3 is a lot more spectacular. Even this footage shows the No.3 getting knocked by the bounce of the left wheel.
Couple of different guns used in the footage, too.
Note that a gun detachment (6) cannot easily assemble/dismantle the gun on their own - two more men are required .
Mike