Fred I would assume that when you IMPRESS rifling with force through the outside of a metal barrel liner tube, tension will be created in the barrel liner tube causing some minor stress and strain in the metal thus some warpage . I have 4 FX barrels and 2 FX rifles. Knock on wood no problems yet. One is an early model Impact, the other is an early model Bobcat that was a .25 and I had a 600mm .22 barrel installed because I wanted the higher capacity air cylinder that only came on the .25 . I assume the slight warpage occurred as the rifling was impressed not when the barrel laiden cart was pushed across the floor. The fact that FX checks and corrects barrels is all I need to know, that and my experience with FX, Diana, Weirich, My old Daisys' and Crosman and Benjamin pumps. If my powder burner barrels get hot, the POI begins to move around so I have to drape a wet towel over the barrel to cool them prior to removing prairie dogs from my uncle's ranch. Never had to do that with any of my air rifles.
