An alternate explanation is that the primer explosion pushes the bullet into the lands, jamming it in place. This causes the burning powder to not have the normal expansion space because the bullet is not moving forward and the force of resistance is greater on a stationary object than a moving object
Ed Matunas said this was the reason "Winchester will never build another .220 Swift rifle." The roughening of the throat by erosion from hot loads made it subject to this sort of stop and go pressure surge.
I am not sold on the concept but it is as good as any of the other wild theories that explain but do not predict.