This is well known to many but not all that Hawke also supplies some of the best airgun ballistics software on the market as a free download. While the BRC software is geared towards their scopes and reticles it will work with most and the Chairgun Pro is airgun/pellet specific. You can get both programs for FREE at:
http://www.hawkeoptics.com/
http://www.hawkeoptics.com/