Please try this experiment...go back to the range and fire three shots as fast as you can....being careful to use proper trigger technique...this is hard but it' s worth it. Do this at least five times allowing proper cool down between groups.

Then take five more three shot groups waiting five minutes between shots.

If either of these groups is significantly better than what you' ve been doing, it implies that your barrel may have a small concentricity problem.....and from what you described it' s going to be nearly impossible to isolate it and fix it......

You didn' t say how far from the second hole the third one hits...if it' s another 1/2 inch, I can assure you that there' s a lot of folks that would love a gun that shoots 1" three shot groups.