Not long ago I watched a cops & robbers program on T.V. N.C.I.S I think. The lab guy took a bullet from a body and lined it up base to base with a bullet fired from the bad guys pistol. He then (under high magnification)turned the bullet till the groove engravings matched, viola! perfect match, guilty as charged! I'm wondering which one of those bullets went down the bore backasswards so that they would match when lined up base to base.

How dare you ask for accuracy.  We know that is the reason that rounds have to be micro stamped in the state of Kalifornicatu.

That way if one of your shells is picked up at a range and found at a robbery/murder/whatever - we will know where you were.

I don't understand your point!  All bullets fired down the same barrel get fired the same way.  Why shouldn't they all then have the same markings the same way, and if the same direction from top to bottome if the barrel grooves haven't been altered?

firing a rd through the bbl, then cleaning the bbl with something like JB bore cleaner will change the tool marks in the rifling not the rifling itself.