Firearm is a term used to refer to small arms, portable guns that can be carried by a single person. The smallest of all firearms is the handgun. There are three common types of handguns: single-shot pistols, revolvers, and semi-automatic pistols. Firearms are also categorized by their functioning cycle or "action" which describes its loading, firing, and unloading cycle. These include manual (Single-shot and repeating), Semi automatic (self-reloading), and Automatic (Gatling, Maxim, Lewis, MG 08 guns), Machine guns (belt-fed ammunition), etc.
These launch one or more projectiles often driven by the action of an explosive force. The force of a projectile is related to the kinetic energy imparted to it, given by the formula Ek =1/2 mv2 where m is the mass and v is the velocity of the projectile.
vCalc's Firearms/shooting library contains such formulas and many more.