So the way I see it, a 1/2 MOA barrel is a 1/2 MOA barrel, no matter what type of rifling is inside it, or what kind of wrap is on the outside of it, and once a bullet has left the barrel, it no longer has any influence on said bullet. (Interior vs exterior ballistics or whatever)
Therefore if the barrel can launch the bullets well then the deciding factors are not the barrel, but the marksmanship ability of the rifleman, and Josh is a fine shot.
Repeatedly nailing a gong at 1400 is no easy thing, but sometimes you just find your groove and everything comes together