Bren light machine gun (UK)

Czechoslovak-made ZGB-30 prototype machine gun in .303 caliber.

Czechoslovak-made ZGB-33 prototype machine gun in .303 caliber.

Bren Mk.1 light machine gun, right side.

Bren Mk.1 light machine gun, left side.

Bren Mk.2 light machine gun.

Bren Mk.3 light machine gun (note the short barrel).


Bren L4A4 light machine gun in 7,62x51 NATO caliber.

	BREN Mk.1	BREN Mk.3	BREN Mk.4	BREN L4A4
Caliber	7,7x57R (.303)			7,62x51 NATO
Weight, kg	10,04	8,76	8,69	8,68 (with bipod)
Overall length, mm	1156	1082	1090	1156
Barrel length, mm	635	565	565	635
Cyclic rate of fire, rounds per minute	500	480	520	520
Feed and capacity	Magazines, box 30 rounds or pan 100 rounds	Box magazine, 30 rounds		Box magazine, 30 rounds

In the year of 1930 British army decided to organize a large comparative trials for a new light machine gun, which included weapons of both domestic and foreign origins. Those included: American Browning Automatic Rifle in .303 caliber, French Darne LMG in same caliber, British Vickers-Berthier LMG, Swiss KE-7 and Danish Madsen LMG. The last entrant, which also was the only one chambered in non-standard caliber (7,92x57 Mauser rather than .303 British) was the Czechoslovak ZB-26 LMG. The ZB-26 was brought to attention of Small Arms Committee during the last minutes before trials by the British Military Attaché in Czechoslovakia. First round of trials resulted in ZB-26 coming the first, and Vickers-Berthier second. As the Darne LMG came too late for these trials, it was included into the second stage of trials, which included Vickers-Berthier and an improved Czechoslovak ZGB-30 LMG in .303 British caliber. Final conclusion of the testing commission was that “ZB gun is of such outstanding design, workmanship and materials as to warrant further serious consideration”. During 1932, the test ZB gun was brought back to Brno for further modifications, which eventually resulted in ZGB 32 light machine gun. According to British requirements, this weapon had a 30-round magazine (earlier prototypes had 20-round magazines) and receiver which could recoil against a special buffer – a feature that significantly decreased felt recoil of the gun. The ZGB 32 was tested, and this resulted in more requirements from the British side, including lower rate of fire and slightly abbreviated barrel. The modified ZGB 33 LMG were tested in January 1934 with great success, and final trials between ZGB 34 (next improved model) and a heavy-barreled Vickers-Berthier were held in August 1934. The net result of this 50 000-round endurance test was the recommendation of ZGB 34 for adoption by British army. The licensing arrangements with Československa Zbrojevka Brno permitted the manufacture of a new gun, designated as BREN (for Brno and Enfield), at Royal Small Arms factory in Enfield Lock. Production preparations were commenced late in 1934, and by early 1935 all manufacturing documentation was converted from metric to inch scales. First Bren Mark 1 light machine gun left the Enfield factory in September 1937.

During the WW2 period, Bren guns were also made in Canada by John Inglis Co and in Australia by Lithgow Small Arms factory. Throught the WW2 Bren machine guns proved to be highly effective, reliable and very accurate weapons. During the war, the Bren guns were gradually simplified and lightened, resulting is a series of Marks, from original Mark 1 and up to Mark 4. At the same time, Inglis Co in Canada produced a number of Bren guns in 7,92 Mauser caliber for China.

When the UK has jointed the NATO in 1954, it solved the problem of the light machine gun in new standard caliber (7,62x51 NATO) by simple adaption of the Bren to the new cartridge. This was relatively easy effort, because 7,62NATO round shares same base dimensions with 7,92x57 Mauser round, which was used in Canadian-made Chinese contracy Bren guns. Therefore, early conversions to the NATo standard included "Chinese contract" bolts, new barrels, magazine adaptors and new magazines. These "NATO standard" Bren guns received official index L4 and also went through a number of modifications. Bren L4 light machine guns served until 1980s, and were quite popular among the British troops.

The BREN is a gas-operated, air cooled, selectively fired machine gun. It has a quick-detachable barrel and fires from an open bolt. Under intense fire (about 4 magazines / 120 rounds per minute) the barrel should be replaced every 300 rounds. The action of gun is powered by a long-stroke gas piston, located below the barrel. The gas block is mounted on the thin tubular sleeve which goes around the muzzle end of the barrel and forms the conical flash hider at the front. Gas block has a manual gas regulator with four settings. The action is locked by tipping the rear of the bolt (breechblock) upwards, and into a locking recess in the receiver. The return spring is located in the butt of the weapon, and is connected to the bolt carrier / gas piston via a long rod; additionally, there is a short spring buffer located below the return spring at the juncture of the receiver and butt, which acts against the whole receiver which is permitted to recoil short distance on the long rails of the trigger housing / butt group. This system significantly decreases felt recoil during fire. The charging handle is located at the right side of receiver and does not reciprocate when the gun is fired. On later marks of the gun it is of folding type.

The ammunition feed is from top-mounted box magazines. These are made from sheet steel and hold 30 rounds in a two-row configuration (although in the field soldiers preferred to load only 27-28 rounds to reduce strain on the magazine spring and thus ensure reliability of the feed under harsh conditions). The Mark 1 BREN guns were also provided with spring-powered flat pan magazines, which held 100 rounds. Such magazines were issued mostly for anti-aircraft applications, and were dropped from latter Marks because of complexity and cost. The magazine housing has a sliding dust cover which is slid forward to load the gun. Spent cartridges are ejected downwards. The ejection port is normally closed with its own dust cover which opens automatically once the trigger is pressed.

The trigger unit permits both single shots and automatic fire, selectable through a safety / fire mode selector lever situated at the left side of the pistol grip. The gun fires from an open bolt and the spring-loaded firing pin is operated by a projection on the bolt carrier, once the bolt is fully in battery and locked.

Because of the overhead magazine, the sight line is offset to the left, and the front sight is mounted on a base which protrudes upward and to the left from the gas block. Standard furniture consists of an integral folding bipod, which is attached to the gas cylinder tube, wooden pistol grip and butt with a spring-buffered buttplate and a folding shoulder rest plate. Mark 1 BREN guns were also equipped with folding grip below the butt. Despite the fact that the BREN, like its predecessor ZB-26 was mainly intended for the light machine gun role, it was also offered with a sustained-fire tripod, and provided with a sufficient supply of full magazines and spare barrels it could serve (to some extent) as a medium machine gun. The same tripod was also adaptable for the AA role. Dual gun mounts were used for anti-aircraft role and on certain land vehicles, used for Commando “hit-and-run” missions during WW2.

Modifications:
ZGB: Czechoslovak-made BREN-type guns, produced for export during early post-WW2 period in .303 caliber
BREN Mk.1: original version with radial type sight, and additional grip under the butt (not present on latter marks)
BREN Mk.1(M): Canadian-made version, with simplified non-telescoping bipod legs and simplified butt without shoulder rest and buttplate buffer; also was made in 7,92x57 calibre for China
BREN Mk.2: Simplified war-time version with simplified rear sight
BREN Mk.3: Lightened version of the Mk.2, with barrel shortened by 70mm (2 ¾ inch)
BREN Mk.4: Minor variation of previous mark, with different butt shape
BREN L4A1: Bren Mk.3 guns converted to 7,62x51 NATO ammunition using Canadian-made 7,92x57 bolts (Chinese contract) and new barrels and magazines; each gun was issued with two barrels
BREN L4A2: Same as L4A1 but with lighter bipod
BREN L4A3: Bren Mk.2 converted to 7,62x51 NATO the same way as L4A1
BREN L4A4: Similar to L4A1 but barrel is chrome-lined; only one barrel was issued per gun (no spare barrels at unit level)
BREN L4A5: same as L4A3 but with chrome-lined barrels. Issue was limited to British Navy
BREN L4A6: L4A1 re-issued with chrome-lined barrel
BREN L4A7: Conversion of Bren Mk.1 to 7,62x51, proposed for Indian army; not produced
BREN L4A8: Not produced
BREN L4A9: L4A4 modified with addition of the sight bracket for AA or Night/IR sighting equipment