Hi

Technicaly all scopes with vertical adjustment can do this - your simply adjusting the holdover to zero for any given distance/pellet/gun combination once you have done your range testing. However in todays market a good example of what (I think) you want would be somthing like a "Big Nikko" which has a 10-50x60 spec. This give you a big magnification to tell the difference in ranges as you have to focus it to make the image clear at any given range - so 30m is clear, 35m is slightly blurred, so you can adjust the focus to make 35m clear, and thus you have your distance/range to known distances/markers. This is different to just using a simple elevation turret which in todays scopes would seldom be used for your purpose due to inaccuracy at air gun distances. Once you mark up your scope with the distances on the focus ring/wheel, you know the distance/range for any given point - on a scope like the Big Nikko, your probably accurate to 2m with practice, you can then adjust your holdover with the elevation adjustment (clicks - up/down).

The Big Nikko is around £450 second hand or £750 new, cheaper scopes are generally not as good, less repeatable, but you get what you pay for.

This is just a rough idea - there are loads of articles in the forum/internet on how to do this for "FT" range finding.

James