I guess Bryan has the facts concerning barrel movement that has long been argued especially by Eric Higgins on "Believe the Target" with Erik Cortina. Tim Sellars has also agreed the barrel does in fact move prior to the bullet exit point.
bulletin.accurateshooter.com
Videos Reveal Rifle Movement Before Bullets Exit Bore of Barrel « Daily Bulletin
This report is from Bryan Litz and the ScienceofAccuracy.com website. As long as there have been rifles, there has been a debate as to how much – if any – the rifle moves prior to the bullet exiting the bore.