In modern parlance, a gun can be a projectile weapon using a hollow, tubular barrel with a closed endâthe breechâas the methods of directing the projectile (and various purposes, for example backing the projectile's trajectory, aiming, as an expansion appropriate slot for propellant, etc.), and firing within a generally flat trajectory. The concept of a "gun" has also taken for a more generic meaning, by which it has come to refer to any one of several trigger-initiated, hand-held, and hand-directed accessories, especially with an increasing bore, which thereby resemble the class of weapon in either form and concept. Examples of this usage include staple gun, nail gun, glue gun, grease gun. Occasionally, that tendency is ironically reversed, such as the case of the Us M3 submachine gun which carries the nickname "Grease Gun". Most guns are described by the kind of barrel used, the means of firing, the purpose of the weapon, the caliber, or the commonly accepted name for a particular variation. Barrel types include rifledâa series of spiraled grooves or angles inside barrelâwhen the projectile requires an induced spin to help stabilize it and smoothbore in the event the projectile is stabilized just by other means or rifling is undesired or unnecessary. Generally, interior barrel diameter along with the associated projectile size is a means to identify gun variations. Barrel diameter is reported in just a few ways. The more conventional measure is reporting the inside diameter of the barrel in decimal fractions in the inch or in millimeters. Some gunsâsuch as shotgunsâreport the weapon's gauge orâas in certain British ordnanceâthe weight in the weapon's usual projectile. A gun projectile can be a simple, single-piece item like a bullet, a casing containing a payload like a shotshell or explosive spend, or complex projectile like a sub-caliber projectile and sabot. The propellant may be air, an explosive solid, or an explosive dissolved. Some variations like that Gyrojet and certain other types combine the projectile and propellant into a single item. My websites: Why Buy Discount Paintball Guns?