Thanks for the link
The story of the EM-2 and its ammunition is told in detail in 'Assault Rifle: the Development of the Modern Military Rifle and its Ammunition' by Max Popenker (of the guns.ru site linked in the first post) and myself. This is an extract dealing with the ammo development, which was the key to the whole system:
"Next in the field came the British, who in 1945 set up the Small Arms Calibre Panel in order to determine the optimum cartridge for a lightweight rifle. After many calculations and experiments mainly involving rounds of between .25 to .27 inch calibre (6.35-6.8 mm), they reported in 1947 in favour of further development of two alternative designs. One was a .27 inch (6.8 x 46) firing a steel-cored 100 grain bullet at 2,750-2,800 fps (6.5 g at 840-850 m/s), which still retained 81 ft lbs (109 j) of energy at 2,000 yards (1,830 m), a significant figure as the estimated energy required to inflict an injury to an unprotected man is around 60 ft lbs (80 j). The other was a .276 (7 x 43: later redesignated .280 to avoid confusion with earlier cartridges) which was tested with bullets weighing between 8.4 and 9 grams (130-140 grains) at between 747-710 m/s (2,450-2,330 fps). The 130 grain/2,450 fps loading had a retained energy of 100 ft lbs at 2,000 yards (135 joules at 1,830 m). Eventually a loading of a Belgian-designed 9 g bullet at 736 m/s (140 grains at 2,415 fps) was decided on. The .280 calibre (actually 7 mm, with a .276 inch bore and .284 bullet) was a little larger than was thought ideal but it was selected for further development, reportedly in order to try to meet American preferences for good long-range performance. For the same reason, the original case rim diameter was increased slightly to match that of the American .30-06 to enable them to rebarrel existing guns more easily, leading to a change in designation to .280/30.
In conjunction with the .280 two new rifles were developed, the EM-1 and EM-2 bullpups, described in more detail in the section on the UK. It is important to note that, unlike the FCARs described above, the .280 was intended to replace entirely both the 9 mm SMG and the .303 inch rifle / MG rounds. It was envisaged that the rifle would normally be used in semi-automatic mode at ranges in excess of about 150 metres, with fully-automatic fire being used in short bursts at shorter ranges. The .280/30 cartridge was formally adopted in August 1951 as the '7 mm Mk 1Z', at the same time as the EM-2 was adopted as the 'Rifle, No.9 Mk 1'. But fate was about to disturb these careful plans.
Towards the end of World War 2 the USA had also begun thinking about replacing the .30-06 cartridge and associated weaponry, and had developed the concept of a selective-fire 'Lightweight Rifle'. What they really wanted was the selective-fire .30 M2 Carbine but with the hitting power of the .30 Garand, at a weight of 3.2 kg (7 lbs). It was rather ambitiously hoped that this one weapon would replace the M1 Garand and the .30 Browning Automatic Rifle (both in 7.62 x 63), the M1/2 Carbine in 7.62 x 33, and the M3 SMG in .45 calibre (11.5 x 23). The Lightweight Rifle was intended to chamber a shorter cartridge than the 7.62 x 63, but still with a reasonable long-range performance so it could entirely replace the older round; it was required to have "a stopping and wounding power which shall not be less than that of the standard calibre .30 ammunition [7.62 x 63] fired from the M1 at ranges of 400, 800, 1,200 and 2,000 yards [up to 1,830 m]". Many experiments followed but, contrary to all of the logic of ammunition design, the US Ordnance Department decided that they wanted to retain the .30 inch calibre. The Americans accordingly ended up with what was simply the .30-06 case shortened from 63 to 51 mm, but with a very similar performance at around 3,500 j (2,600 ft lbs) muzzle energy (made possible by improvements in propellant technology) and therefore very similar recoil. Inevitably, this meant that the planned new selective-fire rifle would prove uncontrollable in fully-automatic fire, and so it proved years before the M14 (based on the old .30-06 M1 Garand) finally entered service.
Interestingly, American opinion on this subject was far from united. The EM-2 and its .280 cartridge were thoroughly tested in the USA in 1950 alongside the FN FAL in the same calibre (the Belgians being enthusiastic supporters of the British concept) and in comparison with the American T25 prototype rifle. This was chambered for the original "T65" cartridge, a 7.62 x 47 round which was the first stage in the development programme which eventually led to the FA-T1E3 case (and associated T65E3 ball loading), later adopted as the 7.62 x 51 NATO. Testing took place at Fort Benning where the US Army Infantry Board was based, and the tests were expected to result in the choice of a new standard rifle cartridge for NATO.
At Fort Benning, the Trials Board reported on the cartridges as follows:
"That the T65 Cal .30 is not satisfactory because of its excessive recoil, blast, flash and smoke. That the Cal .280 is not satisfactory because of its comparatively high trajectory. That of the two basic types of rounds submitted for test the British calibre .280 is preferred."
The detailed findings from the Fort Benning tests showed that while the T65 had a flatter trajectory and produced more severe wounds at ranges of less than 1,000 yards (900 metres), the British round became more effective at longer ranges because of its superior ballistic coefficient. At 1,000 yards the .280 could penetrate body armour 70% of the time, compared with 60% for the .30. The British cartridge also produced considerably less flash and smoke. Most significantly, while the T25 was found to be the more accurate rifle and achieved more hits per minute when fired from a bipod, the EM-2 was far superior in this respect when fired from the shoulder.
Clearly, the British designers had achieved all that they had aimed for, but the Trials Board recommendation to focus development on the .280 cartridge was rejected by the Chief of Staff of the US Army. This was due to the clear preference of the Ordnance Department and the American senior military, political and industrial establishment in favour of a full-power .30 calibre rifle of US origin.
The British felt that the Aberdeen trials should have settled the matter so didn't give up easily. They set about meeting the American objections by producing more powerful versions of their cartridge, with the support of Belgium and Canada. The first change was to upload the 43 mm case to 2,550 fps (777 m/s) with the 140 grain (9 g) bullet, to meet the criticism of the trajectory and also to address complaints that the low temperatures of Arctic conditions reduced the performance to an unacceptable level. This raised the energy remaining at 2,000 yards to 126 ft lbs (170 joules). However, the British cause was severely damaged by a change of government, which led early in 1952 (reportedly followed a meeting between the US President Truman and Winston Churchill, the new Prime Minister) to a decision to rescind the adoption of the EM-2 and its 7 mm cartridge before any had been issued.
Despite this setback, Britain, Belgium and Canada combined (in the 'BBC Committee') to make one last attempt to develop a new 7 mm round which would be acceptable to NATO. Various lengthened cartridges with such designations as 'Optimum', 'High Velocity', 'Compromise' and 'Second Optimum' were developed, mostly with 49 mm cases although the final attempt was simply the 7.62 x 51 necked-down to 7 mm. Muzzle velocities were in the range 2,750-2,800 fps with the 140 grain bullet (9 g at 840-850 m/s). However, the Americans would not be convinced. In any case, the recoil had by this time increased significantly and the balance of the original EM-2 concept had been lost. At the end of 1953, the BBC Committee reluctantly bowed to American pressure and the 7.62 x 51 was formally adopted as the new NATO cartridge.
The only result of all of this effort was a 7 x 49 cartridge, known as the 7 mm Medium, which saw service in an FN FAL selective-fire rifle which was sold to Venezuela."
Tony Williams: Military gun and ammunition
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