The muzzle of a firearm

Firearm

A firearm is a weapon that launches one, or many, projectile at high velocity through confined burning of a propellant. This subsonic burning process is technically known as deflagration, as opposed to supersonic combustion known as a detonation. In older firearms, the propellant was typically...

 is the end of the barrel

Gun barrel

A gun barrel is the tube, usually metal, through which a controlled explosion or rapid expansion of gases are released in order to propel a projectile out of the end at a high velocity....

 from which the projectile

Projectile

A projectile is any object projected into space by the exertion of a force. Although a thrown baseball is technically a projectile too, the term more commonly refers to a weapon....

 will exit.

Precise machining

Machining

Conventional machining is a form of subtractive manufacturing, in which a collection of material-working processes utilizing power-driven machine tools, such as saws, lathes, milling machines, and drill presses, are used with a sharp cutting tool to physical remove material to achieve a desired...

 of the muzzle is crucial to accuracy, because it is the last point of contact between the barrel and the projectile. If gaps exist between the muzzle and the projectile, escaping propellant gases may spread unevenly and deflect the projectile from its intended path (see transitional ballistics

Transitional ballistics

Transitional ballistics, also known as intermediate ballistics, is the study of a projectile's behavior from the time it leaves the muzzle until the pressure behind the projectile is equalized, so it lies between internal ballistics and external ballistics.-The transitional period:Transitional...

).

In the case of rifled

Rifling

Rifling is the process of making helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis...

 weapons, the contour of a muzzle is designed to keep the rifling

Rifling

Rifling is the process of making helical grooves in the barrel of a gun or firearm, which imparts a spin to a projectile around its long axis...

 safe from damage, so it is commonly recessed or protected by a convex "crown".

When firing a gun, a flash is often seen at the muzzle (known as a muzzle flash

Muzzle flash

Muzzle blast is the term used to describe the release of high temperature, high pressure gases expelled from the muzzle of a firearm when it is discharged. Muzzle flash is the term used to describe the visible light of the muzzle blast. The blast and flash are caused by the combustion products of...

) and is produced by the hot gases escaping the barrel. The size of the flash depends on various factors such as barrel length, type and amount of powder, etc. Flash suppressor

Flash suppressor

A flash suppressor, also known as a flash guard, flash eliminator, flash hider, or flash cone, is a device attached to the muzzle of a rifle or other gun that reduces the visible signature of the burning gases that exit the muzzle. This reduces the chances that the shooter will be blinded in dark...

s are attached to the muzzle of the weapon to diminish these effects.