Well here is what I know, but I was in the Army before ACOGs and grew up bird hunting, not deer hunting, long range shooting, etc.
It gets complicated when you are trying to use a fixed-mag scope with dual reticles and a BDC. You are trying to do the following:
- optimize your settings for both bullet types (super and sub)
- focus on accuracy for supersonic, and check your BDC
- learn your bullet drop compensation (BDC) for subsonic real well as it varies slightly by round, etc.
So you ideally put the center at your common zeros for supersonic, like 35 and 100 yds. If you shoot something at say, 20 yards, you actually have to aim high, like at the 200 yard point on the BDC. (see why below).
Then once you swap over to subsonic, you to test your BDC to make sure that at 50 yards your diamond is tip or bottom or some "Kentucky Windage" that you know real well. You have to do that for each diamond if you want to be most accurate.
300 BLK Dual Reticle:
Why you can have two zeros (or even one) - bullets always drop once they leave the barrel (my picture is horrible as it looks like the bullet goes up and then back down, when it doesn't). Your site is angled down at the nose, so that you can have two points where the bullet crosses your eye's line of sight.
All of this is just me messing around - I think the Army just tells you to site in at 100 yards and use your BDC for close range - not sure. Of course, they have M16/M4, not 300 BLK so that is why I am doing this.
You can play with these for your rounds and caliber, etc:
Kestrel® 5700 Ballistics Weather Meter with Hornady® 4DOF® Combining complete onsite environmental measurements with the precise trajectory solutions of the integrated Hornady 4DOF® ballistics solver, this rugged all-in-one...
www.hornady.com