Nope, not necessary to re-zero...I've shot 3 different barrels on the same frame, switching them out between 3 shot groups for each barrel to keep the barrels cool, for several hours at a range session. Never had a POI change. This was with .25-06, .243 and .223 on one frame. Just make sure you tighten the forend screw the same each time. Having a torque screw driver makes this easy, but using a witness mark on the screw will also work....consistency is the key. :wink:
Tim
Tim