I have a 243 Ackley that I am looking to rebarrel. I have read about tight neck barrels but have never had one. I have turned necks and have all the proper measuring equipment. What I have no doubt read before but forgotten is the numbers part of the game. I would like to know how many thousands clearance is needed (ie safe) between a loaded round and the chamber. Maybe .002" total, with .001" on each side? Also, some make brass to have a tight fit and claim they never have to size brass, what would the clearance on this be? Anyone with experience in standard vs. tight neck chambers in custom barrels please chime in. I would like to hear all experiences. I plan on using a #5 fluted Pac-nor 27" stainless on a M700 short action with a 1-12" twist to shoot 70 and 75 ballistic tip and VMax type bullets. Rifle will be pillar bedded with aluminum pillars and Marine-Tex, with floating barrel. I would like to have rifle shoot in the 4's if possible, and wonder if going with the tight neck is needed. I don't mind doing the extra work if it can significantly shrink my groups, like maybe 0.1" @ 100 yards. Thanks for the imput fellers, appreciate it.