My understanding is that the BDC for the rear sight is a menagerie of bullets, barrel lengths, and muzzle velocities averaged into something that will get hits center of mass give or take 5" from 200 to 600 meters. I don't know if I'd trust the accuracy of that little BDC wheel necessarily, but it does give you some rudamentary elevation adjustment, which is nice. If you're shooting at targets ranged in yards you'll have to remember that the BDC is in meters so there won't be a direct correlation (e.g. 400 yards doesn't equal "4" on the wheel).
Below is target range in yards, conversion to meters, and my best guess for the sight setting and hold based on a full size IPSC without knowing the full ballistics of your rifle.
200 yds - 186 meters - "2" Dead On
300 yds - 274 meters - "3" Dead On
400 yds - 365 meters - "350 setting" Hold Shoulder Line
500 yds - 457 meters - "450 setting" Dead On
600 yds - 548 meters - "550 setting" Dead On
When zeroing, leave the BDC knob on "2", use the small aperture, make elevation adjustments with the front sight, and windage adjustments on the rear sight. I would zero about 1/2" high or so of center at 50 yards and confirm point of aim, point of impact at 200 yards. If you need to make small adjustments use the front sight for elevation, rear for windage still. After that start stepping out the distance, writing down the sight settings, where you had to hold on the target, and the results. Good luck.