The rifle will not shoot sub-MOA one minute then not perform the next without introducing shooting error. All variables being equal, it will produce equal results if the shooter maintains form. 500 and in, you can get away with alot of inconsistencies. 600 and out, they immediately show up.
Once your scope mounting is quickly verified, clean your rifle, and either on your tv or handheld device, open YouTube, search for "Snipers Hide Recoil Management" and watch Frank Galli's videos on shoulder pocket, grip, fire-control, setting up behind the rifle, recoil management, all of it. Get on the living room floor and start practicing. Shooting at distance only does one thing: exaggerates poor form of an inexperienced and uneducated shooter.
Good luck!