he can put 15 rounds into a 1.5" at 25 yards he don't need any more stinking training. just buy some tactical pants that's all you needTake all of the time and money you planned to spend on this endeavor and put it toward ammunition and quality training. Work on that consistently for at least a few years to become as proficient as possible under varied circumstances; favoring high stress and unconventional positions.
You are wasting your time and money trying to decide the best caliber for you until this is accomplished.