Hopefully you can get within "spitting" distance of them. He He!!!!!!

Seriously, we used to chase them in our 4WDs up in the northern western desert areas and some were pretty big and quite fast on the move. We weren't allowed firearms in our work camp so didn't shoot any. Depending on the type of country you have to hunt I would think something in the 7mm or 30cal range to reach out and retain energy would do the trick. 7mm Mag would be my choice. They are not dangerous at range so I wouldn't think anything more than a deer rifle is needed.