if the barrel has been shot you can probably swap in a new bolt without worrying about the HS. HS only gets longer with use. this is assuming the barrel bolt combination was correct to begin with. contray to some beliefs the HS is a combination of the distance from the datum line in the chamber to the face of the bolt. the HS dimension on the bolt is the back of the lugs to the bolt face.  if either of those parts is wrong the HS will be incorrect. don't worry about the "bolt lapping" arguement, Sam does it all the time. short HS is more of a concern than long HS.