The 'Chairgun' ballistics computer program is your friend.

It introduced me to the concept of 'ballistic coefficient' which I'll try to define as the degree to which a design of pellet retains its energy as it travels downrange.

It's a bloody marvelous downloadable program. It's basically a friendly spreadsheet where you can input what you know about your shooting parameters, then it will calculate and display a few more, including a trajectory chart showning pellet drop over distance. And it already 'knows' a lot of the popular pellet types.