Problem 1) Heat distortion on the barrel....Problem 2) Mental fatigue from concentrating on any individual group...I have found in the past that when I am watching each shot in any group, I will throw one, or more, out due to losing concentration on the initial point of aim...
I perform much better when I forget the point of impacts and just focus on my sight picture, then my groups tend to be tight...
If you fired more shots than three in reasonably fast time, anything less that a bull barrel will distort to some degree...The longer the distance, the more pronounced the distortion...
