As their recoil is significantly reduced compared to full-power cartridges, fully automatic rifles firing intermediate cartridges are relatively easy to control. However, even though they are less powerful than a traditional full-power cartridge, the external ballistics are still sufficient for an effective range of 300–600 metres (330–660 yd), which covers most typical infantry engagement situations in modern warfare.[2] This allowed for the development of the assault rifle, a type of versatile selective firesmall arms that is lighter and more compact than traditional battle rifles that fire full-power cartridges.
The first known early intermediate cartridge to see service was the 10.4x38mmR Swiss used in the Vetterli rifle which gave it controllable handling and a then high-capacity magazine of 12 rounds. Predominant intermediate cartridges in mainstream circulation came around 50 years later and saw widespread use with the German7.92×33mm Kurz used in the StG 44 and the .30 Carbine used in the American M2select fire carbine during the late years and closing days of World War II.[1][3][4]
With the data collected during World War II and the Korean War, the benefits of intermediate cartridges became apparent. This resulted in the development of "modern" cartridges such as the Soviet 7.62×39mm M43 (used in the SKS, AK-47 and AKM).
Later an international tendency emerged towards relatively small-sized, lightweight, high-velocity Intermediate military service cartridges. Cartridges like the American 5.56×45mm M193 (1964; originally used in the M16), Soviet 5.45×39mm M74 (1974; used in the AK-74, which replaced the AKM), Belgian SS109 / 5.56×45mm NATO (1980; used in most AR-15 systems), and the Chinese 5.8×42mm (1987; used in the QBZ-95) allow a soldier to carry more ammunition for the same weight compared to their larger and heavier predecessor cartridges, have favourable maximum point-blank range or "battle zero" characteristics and produce relatively low bolt thrust and free recoil impulse, favouring lightweight arms design and automatic fire accuracy.[5][6]
History
The 10.4x38mmR Swiss is an early example of an Intermediate cartridge.
In the years leading up to World War I, the Lebel set an international example, and smokeless powder high power service cartridges and service rifles began to be produced by all the world's great powers. This included, but was not limited to, the German Gewehr 98, the British Lee–Enfield, the Russian Mosin–Nagant, and the American M1903 Springfield. These rifles weighed over 8 lb (3.6 kg), and they were longer than 40 in (1,000 mm) and as such were generally inappropriate for close combat. They fired cartridges and featured iron sight lines designed in an age when military doctrine expected rifle shots at ranges out to over 1,000 m (1,100 yd) for simultaneous fire at distant area targets like ranks of enemies, but typical combat ranges were much shorter, around 100–300 metres (110–330 yd), rarely exceeding 500 metres (550 yd).[7]
Introduction of semi- and full-auto weapons as service firearms
World War II revealed the demand for better fire density in infantry operations. To achieve this goal, both Allied and Axis countries rapidly developed and produced a number of semi-automatic service rifles, such as American M1 Garand, Soviet SVT-40 and the German Gewehr 43. Compared to their bolt-action predecessors, these weapons provided a considerably higher effective fire rate. In 1951, the US military published a study on the M1 Garand's fire rate: a trained soldier averaged 40–50 accurate shots per minute at a range of 300 m (330 yd). "At ranges over 500 m (550 yd), a battlefield target is hard for the average rifleman to hit. Therefore, 500 m (550 yd) is considered the maximum effective range, even though the rifle is accurate at much greater ranges".[8]
Simultaneously, armies of both sides had put submachine guns to extensive use. Soviet PPSh-41 and PPS-43, US Thompson, British Sten and the German MP-40 had an even higher fire rate (and thus higher fire density) compared to larger-caliber semi auto rifles, but their effective range was considerably shorter: e.g., 164 yd (150 m) vs 500 yd (460 m) for Thompson and M1 Garand, respectively. SMG, chambered in pistol calibers (7.62x25, 9x19 Parabellum and .45 ACP) lacked penetration provided by larger and faster rifle bullets.
Seeking to combine the rapid fire capabilities of SMG and advantages of the rifle calibers, both Allied and Axis powers developed a range of early automatic rifles. The first automatic rifles to be adopted by the fighting armies were the German FG42 and Sturmgewehr 44.
Demand for lighter ammunition
Although efficient in the battlefield, early automatic rifles had a considerable drawback compared to both semi-automatic rifles and submachine guns. With a fire rate of 600-1000 rounds per minute, automatic rifles increased the amount of ammo a soldier had to carry. However, the ammo was much heavier (393 gr (25.4 g) for 7.62 x 51 round compared to 160 gr (10.4 g) for .45 ACP), effectively limiting the ammo load.
Additionally, when fired in full automatic mode free recoil delivered by full-sized and full-powered cartridges became an issue, too.
Though technically a full-powered cartridge, the first one to fulfil this requirement may have been the Japanese 6.5×50mm Arisaka used by the Russian Fedorov Avtomat rifle, used in limited numbers from 1915 to 1917 (the cartridge itself dates back to 1897). The Fedorov was arguably the first assault rifle.[9][10]
This led to a series of early attempts to produce a lower-powered round using existing calibers. Examples include the US .30 Carbine cartridge for the M1 Carbine and the German 7.92×33mm Kurz, a shortened version of the standard 7.92×57mm Mauser round used in the StG-44, which is more commonly considered to be the first assault rifle.[1][11][12] The Soviets developed a similar round, the 7.62×39mm, for the SKS but far better known as the round for the post-war AK-47.[13]
Post-war developments
These earlier examples were generally developed with the goal being ease of development and logistics, and lacked any rigorous study of their performance. In the immediate post-war era, the British Army began such a study with an eye to replacing its pre-World War I .303 British. The .303 had been slated for replacement repeatedly, but a series of events kept it in service decades longer than expected. Their studies led to a new purpose-designed intermediate round, the .280 British, along with new weapons to fire it. The round attracted significant interest among other UK-oriented forces, but during NATO standardization effort the US was dead-set against any reduction in power.[14] The British EM-2bullpup rifle used an intermediate round, and was issued in limited numbers in the 1950s but the 7.62×51mm NATO was selected and it was removed from service.
In practice, the 7.62×51mm NATO was found to be too powerful for select-fire weapons, as the British testing had warned. When the US entered the Vietnam War it was armed with the semi-automatic M14 rifle while facing increasing numbers of full-automatic AK-47s. Demands for a select-fire weapon were constant but the Army was slow to respond. An ARPA program cleared the way for small numbers of a new and much smaller round, the .223 Remington, to be introduced to combat by special forces. Field reports were extremely favorable, leading to the introduction of the M16 rifle.
Universal service cartridge
Some militaries have considered the adoption of a 'universal service cartridge' – a replacement of small caliber, high-velocity intermediate cartridges and full-power cartridges with a cartridge at the larger end of the intermediate cartridge spectrum, well suited for both assault rifle and general-purpose machine gun use in the 6mm to 7mm caliber range, with external and terminal ballistic performance close or equal to the 7.62×51mm NATO and 7.62×54mmR full-power cartridges.[15]
According to the official C.I.P. (Commission Internationale Permanente pour l'Epreuve des Armes à Feu Portatives) and NATO EPVAT rulings the maximum service pressures range between 320.00–430.00 MPa (46,412–62,366 psi) Pmax piezo pressure
