Lube Purging, which of the following 2 explanations correctly defines it?
Possible explanation #1) - I thought lube purging occurred after several shots were fired, coating the bore with BP fouling that is heavily saturated with bullet lube (softened or liquid). When a subsequent shot is fired, all the soft lube saturated carbon fouling is pushed out of the bore by the bullet acting like squeegee cleaning water off a glass window. The column of muck being pushed forward by the bullet is blamed for causing that shot to be less accurate than the previous shots as it impacts away from the tight group that had been forming prior.
Possible explanation #2) - As the bullets lube groove(s) exit the bore the high centrifugal force generated by the rifling spinning the bullet at high RPM causes the lube in the groove to be flung out of the groove, purging the groove of lube and creates a lube star on the muzzle.
An accuracy robbing problem occurs if the groove is only partially purged creating a rotationally unbalanced bullet which impacts the target off the point of aim out of the group.