It is difficult to range a target, get your gun setup then fire, but it can be done.
I have a Bushnell Elite 1500 that is good at picking up trees, houses barns and the like out to about 1450 yds. I have pickedup deer, cattle, and coyotes out to 800 easily, I might have hit the ground near them I may have ranged them, don't know for sure. I have never tried anything beyond a cow at 800 yds, so it may work further out on some game animals.
What I find best to do on long range varmints is most likely to take a 500 yard shot you are laying on the ground or at a bench of some sort. What I do is I have a little 9" table top tripod (like a $10 item on ebay) and I attach my rangefinder to that, then when I find a target I range it then set up and throw a bullet down range. Most of the time when doing this I also have a spotting scope set up the same way and that is how I find my varmints.