[flashhole]

Never heard of neck bumping, neck sizing is what I think you meant. The Lee Collet Neck Die does not affect any other part of the case except the neck. The collet/mandrel design is very good and the dies work. The bushing neck dies size only the neck w/o the use of an expander ball that gets pulled up through the neck. The bushing design eliminates the possibility of altering the neck with friction from the expander. Conventional neck dies that use expanders work well but require more case prep, especially on the inside of the neck.