I have messed with it a bit but only to check it against my applied ballistics app. I come up with some pretty different numbers between the two. For example, if I input my data from my applied ballistics app for my 6mm XC and the Berger 105gr Hybrid into the Hornady calculator I am getting 2 minutes difference at 1000 yards 24.0 moa vs 26.19. I know the applied ballistics app is right on as I use it all the time so I don't know where the extra drag is coming from. The problem I have with the Hornady calulator is that it has a limited library of bullets to choose from and if your particular bullet isn't in that libraray there is no inputs for your bullet info namely the BC and which BC, G7 or G1. The other problem I have is when using the bullet library it doesn't fill in the form factor category and defaults to 1.0. I feel like if they are going to limit you to a bullet library then all specifications for that bullet should be automatically input into the program. Most shooters know the BC of the bullet they are shooting but few know the form factor for that bullet. In this particular instance the actual form factor is .925. I have to adjust the form factor down to .90 in the Hornady calculator to get me close at 24.43 moa. I am not overly impressed with the Hornady calculator overall but thats just me.