I use Applied Ballistics. It was developed by renowned long range shooter Brian Litz. I have used it to connect at 1,240 meters with a 308, and 2,200 meters with a 338 Lapua. There is a one time $20 download fee but it is totally worth it. Inside the app is a huge bullet library with BCs and everything you need for long range calculations. He has also measured true BC throughout the entire flight path and velocity range. Those can be purchased for an individual bullet for one or two dollars each. You can store several rifle and bullet combinations. The atmosphere conditions when you zeroed can be saved and the app automatically accounts for that when conditions at the range are entered. There are many more features, check out online reviews or the description in the app store.

There are other free apps out there, I have used some but Applied Ballistics has been the best for me.