Calibre is one of the least important aspects of accuracy-- any calibre can be worked on to achieve one hole at any reasonable distance. The projection devices however are a completely different story. In handguns, 22s are easy, all you need is a good barrel, 45s in 1911 patterns are also easy to tune to that level, 38special seems to be intrinsically accurate even in autos like the S&W M52 and 1911 conversions, but getting good accuracy out of a 9mm is a VERY expensive project, a waste of time and money unless the requirements of the game force that calibre's use. So CMP "leg" matches now require 9mm since it is the standard sidearm of US forces, and consequently it costs in excess of $ 3000 to make a Berretta into a 1.5 inch at 50 yards gun. And yes, sometimes the sum of errors involved in the shooting process wind up producing a group smaller than the gun can shoot -- but it is very rare.
Dr. Jim