In firearms, a blowback system is generally defined as an operating system in which energy to operate the firearm's various mechanisms, and automate the loading of another cartridge, is derived from the inertia of the spent cartridge case being pushed out the rear of the chamber by rapidly expanding gases produced by a burning propellant, typically gunpowder or, in the case of large artillery, even dynamite. When a projectile (e.g. bullet) is still within the gun barrel, the high-pressure propellant gas behind it is contained within what could be seen as a closed system; but at the moment it exits the muzzle, this functional seal is broken, allowing the propellant gas to be suddenly released in an explosive muzzle blast. The expanding gas also creates a jet propulsion effect rearward in the barrel against the spent cartridge case. This "blowback" is the predominant component of the recoil. Some guns use energy from blowback to perform the autonomic bolt cycling /reloading process, while others will use a portion of the blowback to operate only certain parts of the cycle or simply use the blowback energy to enhance the operational energy from another system of automatic operation.