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the sealing of the barrel when firing a firearm in order to prevent the forward or backward escape of powder gases.
In guns that load by cartridge, obturation is achieved by the use of a brass cartridge case that expands when the gun is fired and ensures that the barrel is sealed on the breech side. In artillery guns that are loaded separately, obturation is achieved by using special devices in the breech called obturators. Escape of the gases in the direction of shell movement is prevented by the rotary bands of shells and casings of bullets; in mortars it is prevented by annular grooves on the cylindrical part of the shell.