Excellent video Bob!
It seems that the Smooth Twist X barrels for some reason are doing remarkably well with the heavier MK1 and MK2 pellets, maybe even better than the 25.4g King's they were designed for.
My Crown in .25 caliber produced the best groups at 50 yards with the MK2's, not the 25.4g King's I'm used to shooting. I switched over to the MK2's for my Crown. So I guess I'm not surprised by what your testing proved.