Don't try to reinvent the wheel. If you have the money, Leica or Swaro are the optics to buy. Not cheap but they are the best there is. To see a Clay and hits at 2000 yards you are going to need at least 80X magnification maybe even 100, and at that magnification the clay is going to need to be out on a real good background. On top of that, there are not going to be very many days when the conditions are going to allow you to see that small a target that far away.
You say this is strictly for target shooting and not hunting. For that type of shooting you are far better off with a remote camera system. It will work 100% of the time and you can do slow motion replay, etc to review the shots.