The selection of a rifle for use in the sporting pursuit of Tyrannosaurus rex, a rexGun, is so deserving of thoughtful assessment and requires such careful consideration because your life, and the lives of those in your hunting party, may very well depend upon it. The question of how much gun is truly enough to provide a reasonable chance of success against a T. rex is critically important. This work examines the history, use, and terminal ballistics of bullets, cartridges, and rifles suitable for use hunting T. rex. It offers advice and unique formulae that can aid a hunter in the selection of appropriate cartridges and bullets. And, it explores T. rex in ways never before seen in print. Included are numerous photographs and detailed tables. And, to aid with shot placement, a Target Areas Diagram of a Tyrannosaurus rex. Hunters, gun enthusiasts, and dinosaur fans will all find rexGun intriguing, exciting, and hard to put down.