Headspacing… All our barrel assemblies are headspaced at the factory and are shipped ready for assembly and use. Barrel assemblies can be ordered with either a stepped, crowned muzzle (for Post-Ban rifles) or a threaded muzzle for attachment of a flash suppressor or muzzle brake.  BATF rulings permit permanent factory installation of muzzle brakes on certain Post-Ban barrels if overall length equals at least 16". Ask your Bushmaster representative about the variety of muzzle brake options available for Post-Ban barrels
**********************************************************************

This is off the Bushmaster page and my quetion is if I take the bbl off , do i need to have to have the headspacing redone? I have a bushmaster  M4 that I am painting. What do you think ? I dont realy know a lot about the bbl on off procedure.

Removing (and reinstalling??) your barrel will have no effect on headspace as long as you keep the same bolt with that barrel.  It is those 2 items alone that determine headspace, not the upper receiver onto which you attach the barrel.

Ya its only a remove and reinstall. Thanks I dont want to fuc up my gun.

headspacing is not adjustable or easily changed on the ar