I have been shooting wildcat for a few years, where almost all the aspect of reloading are trial and error.
I have not figured it all out yet, and I might be wrong,
but I feel that the bullet jump factor is a function of the burning speed of the powder and the hardness of the projectile (jacket),
and the size and depth of barrel lands and grooves..
With the faster burning powder, you would have to reduce the chamber pressure early at the detonation of the charge.
This is achieved by increasing the detonation chamber (by moving the projectile out) as soon as possible.
Having the bullet jammed to the groove will significantly increase the drag of the projectile,
thus leaving a "jump" space would let to better distribution of pressure curve, and ultimately lends to a better accuracy.
The other end of the theory, which is in contradiction from the above
Is that the energy required to engrave the projectile onto the rifling is very high.
On slower burning powder, this energy pressure came slow,
thus for projectile that sit away from the groves have enough acceleration to carry over the engraving smoothly.
And again, ultimately lends to a better accuracy.
Pardon me to ramble. But thats what I thought.