Don't use rangefinder...it is a bad crutch.
- Ping near the target. It will show you the distance to the ping.
- Adjust your sight to the appropriate range. I normally round, at <= 250, I set to 200, at > 250, I'd set to 300, for example.
- Snipe away.
No need to deal with key bindings. If you bind your keys like you want, and try to shoot a moving target, you will always miss (because you need to lead, and it will be sighting into whatever is beyond where your target often is (and if open air behind target, you will sight int 1000m).