chamber square to barrel

i have started to check POI w/a brass chamber laser @ 20', indoors--i feel i am pretty close to %'s, basis neal winstons formula given to me earlier!---but what i have found , is that some chambers, seem to be untrue with a few going slightly to the left!!(3/8" off to left @ 20'=? @ 30yds??) --shud this be a concern or does the choke straighten this out??