Its where u place a center point in the lathe chuck and 1 in the tail stop then pinch the barrel between those 2 point placing pressure on the crown and chamber then they attach a dog leg to the barrel and use that to turn the barrel.... or the chuck up on the barrels breech area and run a live stop in the crown placing a lot of pressure on it...both these setups easily damage some of the barrels most critical areas

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07/SOT2
NRA Instructor