With 640 acres being a square mile, centerfire rifle catridges capable of going 5X that, and Florida being flatter than 4F feet ..... you all might be launching lottery tix for negative consequences. Your call, though.
Tallahassee isn't real flat. They may very well be shooting into a hillside. If not, they likely have a berm or a steel backstop. At least that's what I picture when I read "homemade range".