The Cranmers make their living from history, and that doesn't mean with books or in a classroom. They sell history, as in rare firearms and military artifacts. ``Family Guns'' opens the doors to International Military Antiques, a business owned and operated by the father-son duo Christian and Alex Cranmer. They buy, sell, trade and restore some of the world's rarest firearms, such as a $40,000 pistol from the Battle of Trafalgar and a $25,000 British Colonial cannon. In order to determine a weapon's actual worth, the IMA team test-fires it, a dangerous undertaking when dealing with a 200-year-old artillery piece. But if it works, the weapon's price can double.