Thanks everybody. This is all superb information for me to start digesting.

I believe I need to go away and understand what ballistic co-efficient actually is and how it can vary before I get deeper on holdovers and the like. That said, I will have a play with the Hawke Chairgun app now....

Rifleman's Firearms sounds like a location directly form heaven! smoked meats and rifles! only an hour away from me too so will have to check it out pretty soon.

I am a note taker, so if there is interest, I could write up my learning and experiments after I get down the range and do this.