You should be using a .48g BLS BB or Novritsch .46g BB, as the BB weight is what gives you a huge part of range and accuracy.
For sighting in your scope, do the following
Set your hop up to where your desired BB weight shoots flat, goes up a little bit, and drops down
Adjust your crosshairs/whatever scope reticle to the highest point the BB reaches
Play the game and modify your gun as needed, it's that simple.
Also, don't expect 100m shots without using a whole magazine, and 85m is probably about the farthest you should shoot until you gain experience, as you'll just waste ammo and may give your position away.
I have an ultra Gucci VSR-10 with even more parts being made, shipped, and saved up for, and I still try to get as close as I can to my opponent as I'd rather get a one shot kill than screw around.
Still, push your limits once you gain experience, then you'll know where you can reliably hit somebody.