Thechamber of afirearm is the cavity at the back end of abreechloading weapon'sbarrel orcylinder, where theammunition is inserted before being fired. The rear opening of the chamber is thebreech, and is sealed by thebreechblock or thebolt.[1][2]
The act ofchambering a cartridge means the insertion of a round into the chamber, either manually or through theaction of the weapon, e.g.,pump-action,lever-action,bolt action, orautoloading operation generally in anticipation of firing the weapon, without need to "load" the weapon upon decision to use it (reducing the number ofactions needed to discharge).[3]
Automatic andsingle-shot pistols (such asDerringers),rifles, andshotguns generally have a single chamber integral to their barrels, butrevolvers have multiple chambers in theircylinder, and no chamber in their barrel. Thus, pistols, rifles, and shotguns can usually still be fired with themagazine removed as long as acartridge is inserted into the chamber, while a revolver cannot be fired at all with its cylinderswung out orbroken open excepting ahang fire or other malfunction.
In firearms design or modification, "chambering" is fitting a weapon's chamber for a particular caliber or round,[4] so aColt Model 1911 ischambered for.45 ACP or.38 Super, orre-chambered for.38/.45 Clerke. While the majority of firearms are chambered for one caliber, some are chambered for multiple calibers; however firing an oversized or undersized cartridge can be hazardous.[2]
In the barrel chamber, fluting refers to gas relief flutes/grooves used to ease the extraction of cartridges.[5][6] They may also come in annular and helical forms.[7] Notable firearms using fluted chambers are theroller-delayed blowbackHeckler & Koch G3 andlever-delayed blowbackFAMAS andAA-52.
Roller or lever-delayed blowback arms require that the bolt starts moving while the bullet is still in the barrel and the spent case is fully pressurized. Fluting the end of the chamber allows combustion gasses to float the neck and front of the cartridge case providing pressure equalization between the front outer surface of the cartridge case and its interior. The roller-delayed blowbackStG 45(M) assault rifle prototypes proved pressure equalization fluting is desirable, since the breech of roller or lever-delayed blowback arms is opened whilst under very high internal cartridge case pressure that presses a spent (bloated) cartridge casing against the chamber walls which can cause significant problems during the cartridge extraction phase. Using traditionally cut (non-fluted) chambers in the StG 45(M) resulted in separated cartridge case heads during testing.
A barrel chamber with pressure relief ports that allows gas to leak around the cartridge during extraction.[8] Basically, the opposite of a fluted chamber, as it is intended for the cartridge to stick to the chamber wall making a slight delay of extraction. This requires a welded-on sleeve with an annular groove to contain the pressure.[9]
Mostly used on artillery guns. Multi chambered is where the barrel has a series of chambers to propel the round down the barrel to increase speed and range. TheLymann-Haskell multi chamber gun is an example.
The chamber is a key component to the practice offorensic firearm examination. The chamber is known to imprint its surface striations irregularities on thecartridge case, in what are called chamber marks, due to the pressure produced whenshooting.[10][11][12] Such imperfections in chamber may be produced in the manufacturing process or through extensive use.[13] Such chamber marks are more pronounced on substandardfirearms or when firing from an undersized chamber.[10]
In recent years there has been a push to automate this process via the use ofautomated firearms databases.[14]Ballistics identification has also seen the development ofmicrostamping technology which purposefully creates chamber marks through engravings on thefiring pin andbreech face.[15]
