Personally, I do not believe that straight edge bit is totally reliable. Many doubles, particularly relatively lightweight ones have their OD's increased in the choke area so they are a bit "Swamped". Also even if proved to be perfectly straight there is still the matter of did they get set to the absolutely correct convergence, which of course can vary a bit according to load used.

Miller/TN
I Didn't Say Everything I Said, Yogi Berra