The Bren is considered to be one of the finest machine guns ever designed despite being a magazine-fed weapon.
The Bren was a light machine gun intended to replace the previous Lewis Gun. Developed and put in production in 1935, BREN Mk.1 was a near identical copy of the Czech ZB-26, customized for United Kingdom standards and requirements (most notable - .303 British ammo). The Bren had a reduced rate of fire and heavy weight to aid controlability. The Bren was know to be reliable, but it had issues like barrel overheating too fast and the fact that it was magazine fed.
Over the time of World War 2, there were two modifications, which were marked Mk.2 and Mk.3 respectively.
The Mk.2 changed the rear sight to a conventional leaf sight, changed the bipod to a fixed-height one, and various steps were taken to simplify manufacture.
The Mk.3 is basically a Mk.1 with a shorter barrel. They where initially intended for jungle combat but ended up being used on every theater of the Second World War.
The Bren L-4 where earlier model converted to fire the standard 7.62 NATO round and where further simplified to keep un with the times. The most notable change is the straighter magazine. Variants include the L-4A1(modified Mk.3), L-4A2, L-4A3(Royal Navy model), L-4A4, L-4A5(developmental model - never built) and the L-4A6.
There was also a Chinese variant converted to fire the 8mm Mauser and 7.62 Russian rounds.
BREN had stayed in service until 1991 where it saw service during Gulf War 1. Though officially, BREN is no longer in service, British Army and Navy still have a substantial number of L4A4 and L4A6 in stock. Additionally, BREN guns are still in use in countries which imported British weaponry, like India where it is manufactured as the Machine Gun 1B.
Technically, BREN is gas-operated, air-cooled, magazine-fed machinegun. Magazines fit 30 cartridges, and are inserted from top - one of the trademark characteristics of the BREN. Due to that, sights are offset to the left. Another unusual feature is that barrel and bolt assembly can roll back within the receiver, thus dampening recoil. Barrel is quick-changeable, and most of BREN guns are shipped with replacement barrel. (L4A4, L4A5 and L4A6 modifications have chromed barrel and chamber, and thus, were shipped with single barrel.) All BREN guns are fitted with bipods.
Overall, the BREN is reported to be very reliable, accurate and efficient machinegun, and although no longer in British Service, it is still used around the world today.