The light gun and its ancestor, the light pen, are now rarely used as pointing devices due largely to the popularity of the mouse and changes in monitor display technology—conventional light guns only work with CRT monitors.
Modern screen-based light guns work by building a sensor into the gun itself, and the on-screen target(s) emit light rather than the gun. The first device of this type, the light pen, was used on the MIT Whirlwind computer.
. The speed of a shock wave at such high temperature and pressure is much faster than that of any bullet, and would leave the gun as sound either through the barrel or the bullet itself rather than contributing to the bullet's velocity.
. This is because much of the energy generated in detonation is in the form of a shock wave, which can propagate from the gas to the solid structure and heat or damage the structure, rather than staying as heat to propel the piston or bullet.
This principle is similar to that of internal combustion engines, except that the bullet leaves the barrel, but the piston transfers its motion to other parts and returns down the cylinder. As in an internal combustion engine, the combustion propagates by deflagration rather than by detonation, and good gunpowder, like good motor fuel, is resistant to detonation.
Most guns use compressed gas confined by the barrel to propel the bullet up to high speed, though devices operating in other ways are sometimes called guns. In guns that are firearms the high pressure gas is generated by combustion, usually of gun powder.
Shotguns are normally civilian weapons used primarily for hunting. These weapons are typically smooth bored and fire a shell containing small lead or steel balls. Variations use rifled barrels or fire other projectiles including solid lead slugs, a Taser XREP projectile capable of stunning a target, or other payloads. In military versions, these weapons are often used to burst door hinges or locks in addition to antipersonnel uses.
In civilian use, a related item used in agriculture is a captive bolt gun. Such captive piston guns are often used to humanely stun farm animals for slaughter.
Autocannon are automatic guns designed primarily to fire shells and are mounted on a vehicle or other mount. Machine guns are similar, but usually designed to fire simple projectiles. In some calibers and some usages, these two definitions overlap.
The word cannon is retained in some cases for the actual gun tube but not the weapon system. The title gunner is applied to the member of the team charged with operating, aiming, and firing a gun.
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