I'd suggest you write a very simple app in Python. I know you said you didn't know programming, but the maths here are pretty simple as is the ui (and you could start by just doing the calculation and outputting it in the terminal).

If you're interested, I'm sure people will be happy to help with code snippets, etc. First thing you should do though is to find a page which list the governing equations (assuming they are any more complex than basic A-level maths) and the relationship with the various bullet/grain types (which will presumably change the initial velocity and drag for the bullet), presumably these are tabulated somewhere as people must have done this before the invention of mobile phones?