After World War II, the UK sought to modernize its small arms, many of which were based on designs originating from before the First World War. For its medium machine gun, the British were still using the reliable but increasingly obsolete Vickers water cooled gun in .303 caliber. With the adoption of the 7.62 NATO by the UK, trials were held to select a new air-cooled general purpose machine gun, which resulted in the adoption of the excellent Belgian MAG. In these trials, however, was tested a belt-fed variant of the magazine-fed Bren gun, called the X11E4. This gun is the subject of an article over at The Armourer’s Bench, as well as an accompanying TAB video, embedded below:
Although based on the reliable and solid Bren gun, the X11E4 contained a fatal flaw. Its belt feed mechanism operated via a curved surface on the side of the bolt carrier, which interacted with a rotating element which actuates the feed pawl. The problem with this is that the force applied to the rotating element worked against a substantial mechanical disadvantage, meaning that the effect of dirt and grit on any of the moving elements in the feed pawl was magnified relative to the force exerted on the bolt. Therefore, in order to work properly the X11E4 needed to be heavily lubricated, or its bolt could stop due to the resistance from the pawl. In contrast, most modern belt fed machine guns use a long pivoting cam track which works an intermediate lever, substantially improving the mechanical ratio of the bolt’s forward motion to the transverse movement of the feed pawl. This superior method of belt feeding was adapted from the German MG-42 machine gun by the West after World War II. It can be understood via the instructional M240 (itself a derivative of the MAG that won out over the X11E4) video, embedded below:
Ironically, the magazine-fed Bren continued to serve the British Army for many years after the demise of the X11E4, sallying forth into the early 1990s in the guise of the 7.62mm L4 Light Machine Gun.