If you are shooting at a patern plate there two points you may want to consider particulrly with OUs .
1 is the gun being held square on or upright ? It is supprising the number of people that cant a gun into there face so that the barrels are at an angle .
2 is the rib exactly centered and is the bead in the center of the rib? I recently relayed the ribs on a well known make of Italian gun and was supprised to find the rib was originaly one sideded .I have also found it is not uncommon for beads to be off center .OK may be ony a few thou but it all adds up .
