Henry Deringer (October 26, 1786 Ð February 28, 1868) was an American gunsmith. He invented, and gave his name to the Deringer pistol. Further development and copying of his design resulted in the derringer pistol that was generically manufactured widely by other companies. Nicely engraved nickel silver furniture. A gun's caliber is determined by the diameter of the barrel and the size of the projectile used measured in inches or millimeters. The derringer used to assasinate President Lincoln had a serial number 99 with a .44 caliber bore. The barrel measures 2 1/8-inches with the gun being 5 5/8-inches in overall length. It has nicely engraved nickel/silver furniture, a brass front sight and is in excellent overall condition. Serial number appears on butt in wood and on the bottom of the trigger guard tang. Nice small size, finely made gun.