Effect of number/type of grooves on velocity

Well, you missed the boat partially. The reason for shooting differently isn't because of groove/bore differences alone.
Certainly that can be a part of it, and by your pressure trace results; proves there isn't much difference between grooves and pressures.
What you have to consider is the whole systems, and not the parts. Those rifles all have the the potential to have differences in:
Chamber dimensions, free bore, bore/groove dimensions, how sharp the rifling ramps to full height, barrel length, barrel harmonics, rifling.

The most likely cause for the pressure differences, are in the chamber and freebore differences.
The most likely cause for the differences in where they shoot, is barrel harmonics.

View the original article here