I doubt it is the shooter, but that makes sense about the breathing and going up and down...im pretty used to shooting rifles and have never had this problem before. The only thing that might be causing a little bit of variation is the slightly heavy trigger pull combined with the magnum load. But then again i shot my remington 1100 slug gun and the trigger pull is super heavy and i can still get about a4 in group with it at 100 yds.
should i run one saturated patch of no. 13 then dry it with 3 patches or should i clean it with several wet patches and several dry ones trying to get it as clean as possible while shooting on the range?