Of course the simplest you can do is to build a mortar.
Nebraska eh? You shouldn't have any trouble finding open places to shoot - but finding a backstop will be an issue.
Golf ball shooters are interesting - it's easy to shoot 100-200 yards with a 2 - caliber long mortar - using a very small amount of powder.
A cannon with, say, an 18" bore will chuck a golf ball size ball of lead well over a mile or so with ease - scary. I've heard of some serious golf ball cannon doing 4000 meters plus.
You've got some serious choices to make.