I've used the Norma site, and it is easy to use, but is somewhat limited in the parameters that you can enter. For a very sophisticated ballistic program check out this one at www.snipercountry.com After you log on, go to the ballistics page and click on the program offered by, I think, JBL advanced version. There are other programs on the site but this one is a very good one.

edit...........I should have said that this program is free to use. It can be used from the website as is.