I'm going to have to go along with SH on this. With barrel diameter and everything else being equal, a longer barrel will have more "whip". This is fine provided it is the same from shot to shot and there is no contact with the stock. A heated barrel will change the pressure where it contacts the stock causing the POI to change enough to notice it on paper. However the longer barrel (up to a point) will give increased velocity because of a more efficient powder burn - i.e.: more consumption. Accuracy between the shorter vs longer barrel itself will not improve with the longer barrel. The reason someone can usually shoot better with the longer barrel is because of the longer sight plane with open sights. A scoped rifle one should notice no difference unless the barrel likes more velocity.