I'll add my .02 cents......
Sized bores do two things (if you match them to your paint)!
Prevent roll-out in closed bolt guns (pumps, cockers, etc)
And will improve shot count some
. Your not sending air around ball since it is sealed better than in larger barrel BUT if it is too tight it will take more air to force it down the barrel.
As far as hitting what your aiming at.....get a nice Smooth and Clean barrel. I have seen stock barrels after some love that shot better than high end kits.
The most important thing......AIM