38” thin wall barrel LH NW trade gun .24ga. Done with trying barrel bending to correct windage problem. .550 ball .018 patch 55gr 3f. Shooting at 35 yards it groups good and consistent. Problem is at that range it shoots 12” to the left. So going to try filing the muzzle at an angle. I assume I need to file on the left side to steer the ball to the right? And about how much do you think would need to be removed in degrees?