I initially test as far as I my range supports(300).
I also generally shoot tighter moa further out. Never could figure out why/how this is, and could never convince any of the experts in shooting of it.
I don't believe it's the bullets, barrel, nor the load. If it were, then this phenomenon would be easily proven. It hasn't been to date(independently validated).
I'm leaning towards parallax. I think at distance, I get a more precise detection of focus than up close where my eyes might naturally compensate for error.
This would explain inconsistancies in my grouping up close, and why my true capability seems to be found further out.
Point blank benchrest shooters might not see it if they only shoot one range per gun. Once parallax is set, they would have no reason to mess with it.
They are also careful to hold position while shooting as fast as possible in it.
I believe long range shooters, who's ranges and shot timing vary, have more challenges than fully understood.