Armament Research Services (ARES) is a specialist technical intelligence consultancy, offering expertise and analysis to a range of government and non-government entities in the arms and munitions field. For detailed photos of the guns in this video, don't miss the ARES companion blog post:
The EM-2 was the rifle that the British pushed for NATO trails in 1950. It was a rifle well ahead of its time in several areas - as a select-fire bullpup rifle, it was intended to replace both the infantry rifle and the submachine gun. Its .280 caliber cartridge was designed with combat ranges of 600 yards and less, acknowledging the reality that engagements beyond even 300 yards were extremely rare, and not important enough to base rifle design on. It was also designed to use primarily optical sights, long before this concept would be embraced elsewhere. Unfortunately, the potential of the EM-2 was lost to the political decision that compatibility with American ordnance choices was a more significant benefit than an improved infantry rifle.
Mechanically, the EM-2 is heavily based on the German G43 flapper-locking system. It uses a long stroke gas piston in place of the G43's short stroke one, though. To help account for the slower handling of a bullpup configuration, the EM-2 would both lock open when its magazine was empty and also automatically close the bolt and chamber a round when a fresh magazine was inserted. The safety was much like that of the M1 Garand, and the selector lever was of the push-through type like on the German Sturmgewehr.
The optic on the EM-2 is quite tiny, and offers no magnification. Its purpose is to reduce the two-element sight picture of traditional iron sights to a single plane that can be more quickly and easily placed on the target.
In total, only 55 EM-2 rifles were manufactured, including the paratrooper model in this video and a number of 7.62mm NATO examples made as a last ditch effort to remain competitive in NATO trials. Where most failed prototype rifles were rejected for very legitimate technical shortcomings, the EM-2 is (I believe) a prime example of an outstanding weapon that fell victim to politics unrelated to its actually qualities.
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