I've tooled around in them a bit, not an expert but...
You're range will be greater then icon range. This accounts for lead and drop.
What I would do is get a friend, go to a field in the rear, main arena and take turns upping a plane while the other shoots at it. You won't kill anything but can work out lead, elevation, time of flight, etc. If you are unable to talk a buddy into it just go to a busy field and shoot at friendly birds. Some will whine and yell but they can't see who is shooting at them.
Final thought, the time of flight is considerable. Take one well aimed shot and do not pull the trigger again until that was has detonated. This is called adjusting fire. You will be surprised how many seconds it takes for a round to travel out to -3k, -5k, etc. If you don't wait you will not be tracking the most recent shot. You won't hit anything by design and will lose confidence in your aim point.
Just some thoughts.
Boo