Barrel chamber flutes are longitudinal grooves cut in the chamber of a firearm that allow propellant gases to surround the fired cartridge case, thereby equalizing internal and external gas pressures, which facilitate extraction or bolt operation in a delayed blow-back firearm design. Flutes are found in the chambers of some semi-automatic and full automatic pistols, semi- automatic and automatic rifles, submachine guns, and machine guns. They vary in number (2 to 18), shape, length, and width, and they leave corresponding impressions on a fired cartridge case. The forensic firearms examiner can often determine the type, model, and caliber of the suspect firearm through examination of the flute impressions on the fired cartridge case. Flute patterns are most often identifiable as swellings of fired cartridge case metal; however, a few are identifiable only as patterns of pronounced firearm discharge residue on the spent cartridge case. The latter must be handled carefully to avoid disturbing the residue pattern through poor handling or rubbing. This article discusses factors that affect the identification value of flutes, the characteristics of an annular grooved barrel chamber, fluted and annular or helical grooved barrel chambers in pistols, fluted barrel chambers in semi-automatic and automatic rifles, and fluted barrel chambers in submachine and machine guns. 18 figures