In 1922, to find a replacement for the Lewis, the Small Arms Committee of the British Army ran competitive trials between the Madsen, the Browning Automatic Rifle (BAR), the Hotchkiss, the Beardmore-Farquhar, and the Lewis itself. Although the BAR was recommended, the sheer number of Lewis guns available and the difficult financial conditions meant that nothing was done. Various new models of light machine gun were tested as they became available, and in 1930, a further set of extensive trials commenced, overseen by Frederick Hubert Vinden. This time the weapons tested included the SIG Neuhausen KE7, the Vickers-Berthier and the Czechoslovak ZB vz.26. The Vickers-Berthier was later adopted by the Indian Army because it could be manufactured at once, rather than wait for the British Lewis production run to finish; it too saw extensive service in World War II. Following these trials, the British Army adopted the Czechoslovak ZB vz.26 light machine gun manufactured in Brno in 1935, although a slightly modified model, the ZB vz. 27, rather than the ZB vz. 26 which had been submitted for the trials. The design was modified to British requirements under new designation ZGB 33, which was then licensed for British manufacture under the Bren name. The major changes were in the magazine and barrel and the lower pistol grip assembly which went from a swivelling grip frame pivoted on the front of the trigger guard to a sliding grip frame which included the forward tripod mount and sliding ejection port cover. The magazine was curved in order to feed the rimmed .303 SAA ("Small Arms Ammunition") cartridge, a change from the various rimless Mauser-design cartridges such as the 8mm Mauser round previously used by Czech designs. These modifications were categorised in various numbered designations, ZB vz. 27, ZB vz. 30, ZB vz. 32, and finally the ZGB 33, which was licensed for manufacture under the Bren name. The Bren was a gas-operated weapon, which used the same .303 ammunition as the standard British bolt-action rifle, the Lee–Enfield, firing at a rate of between 480 and 540 rounds per minute (rpm), depending on the model. Propellant gases vented from a port towards the muzzle end of the barrel through a regulator (visible in the photo, just in front of the bipod) with four quick-adjustment apertures of different sizes, intended to tailor the gas volume to different ambient temperatures (smallest flow at high temperature, e.g. summer desert, largest at low temperature, e.g. winter Arctic).