Intermediate cartridge

An intermediate cartridge is a rifle/carbine cartridge that has significantly greater power than a pistol cartridge but still has a reduced muzzle energy compared to fully powered cartridges (such as the .303 British, 7.62×54mmR, 7.65×53mm Mauser, 7.92×57mm Mauser, 7.7×58mm Arisaka, .30-06 Springfield, or 7.62×51mm NATO), and therefore is regarded as being "intermediate" between traditional rifle and handgun cartridges.

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. This allowed for the development of the assault rifle, a type of versatile selective fire small 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 German 7.92×33mm Kurz used in the StG 44 and the .30 Carbine used in the American M2 select fire carbine during the late years and closing days of World War II.

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.

The late 19th and early 20th century saw the introduction of smokeless powder cartridges with small caliber jacketed spitzer bullets that extended the effective range of fire beyond the limitations of the open rifle sights. The Maxim gun, the world's first machine gun, was devised in 1885, and a year later, the Lebel Model 1886 rifle had the distinction of being the world's first smokeless powder bolt-action rifle.

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).

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".

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.