Going down the route of parametric equations would be the way I'd go about it.
(where D is drag, if your game has no air resistance this is 0)
(mg being the object's weight)
Your horizontal displacement is x(t) and the vertical displacement is y(t). I suspect the AI would know/guess x(t), the gravity is up to you as a programmer and depends on the mass of the shell.
To find the angle you can isolate
You can then divide eq1 by eq2
I'm not sure how correct that is going to be though :\