I use bullet flight on my iPhone and if has worked very well. Also take screen shots of all your info entered. I learned to do this after my 4 yr old deleted the app and all my data was gone. You can reload the app but your tweaked data is gone, so now with the screen shots I can go back and make sure my data fields are the same as they where
I had to look up "shooter ballistics calculator" to get it to show up. Plus, you should have all your aps you've purchased saved on the Apple server and you can redownload it.