Intermediate cartridge

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 sight lines. 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 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 capable out to over 1,000 m (1,100 yd) but typical combat ranges were much shorter, around 100–300 metres (110–330 yd), rarely exceeding 500 metres (550 yd).[2]

Therefore, the potential of the full-power rifle ammunition at longer ranges was seldom needed.

...if hasty wartime training was such that he [the infantryman] had no better than a fifty percent chance of hitting a target at 300 yards (270 m), there was no logical reason to give him a rifle and ammunition designed to kill at 2,000 yards (1,800 m)

— Ian V. Hogg, Modern Small Arms[3]

During World War II, to improve close combat ability, some semi-automatic rifles were created, such as the American M1 Garand and the German Gewehr 43, but for close quarter combat, a more common sight was the submachine gun. Weapons such as the Soviet PPSh-41, US Thompson, British Sten and the German MP-40 had fully automatic fire, and were still easily controllable due to the fact they used pistol cartridges. These submachine guns could provide high rates of controllable fire, but they lacked the stopping power and longer effective range of the battle rifles.

In 1951, the US military published 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".[4] What was needed was a more compact, selective fire weapon, firing a cartridge combining the range and power of a rifle, with recoil nearly as low as a pistol cartridge. The resulting firearm would have the accuracy of the former (within expected typical combat ranges), but able to project the volume of fire of the latter at closer quarters.

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 1915-1917 (the cartridge itself dates back to 1897). The Fedorov was arguably the first assault rifle.[5][6] Later came the US M1 Carbine, which used the .30 Carbine cartridge and was developed as a weapon for officers and rear area soldiers unlikely to be involved in infantry assault but who needed a weapon more effective than a pistol. Soon after came the 7.92×33mm Kurz round developed by the Germans in 1938, which was a shortened version of the standard 7.92×57mm Mauser round, and was used in the StG-44, which is more commonly considered to be the first assault rifle.[1][7][8] When the Soviets developed the AK-47, they already had an intermediate cartridge of their own, the 7.62×39mm, which was used in the SKS, a weapon which saw very limited use in the closing stages of World War II, but was quickly replaced once the AK-47 entered service.[9]

Since the 1960s the United States, NATO, the (former) Warsaw Pact, the People's Republic of China, and other countries adapted relatively small sized, light weight, high velocity military intermediate service cartridges in the form of the .223 Remington (1964), 5.56×45mm NATO (1980), Soviet 5.45×39mm (1974), and Chinese 5.8×42mm (1987). These intermediate cartridges 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 light weight arms design and automatic fire accuracy.[10][11][12] [13][14]

Typical intermediate cartridges have:

• Necked cartridge
• 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 340.00–430.00 MPa (49,313–62,366 psi) P_max piezo pressure
• muzzle energies ranging between 1,250–2,500 J (922–1,844 ft⋅lbf)
• Muzzle velocities ranging between 700–950 m/s (2,297–3,117 ft/s)
• Relatively low O_ratio's ranging between 4.29 and 7.99

• List of assault rifles
• Table of handgun and rifle cartridges
• Fully powered cartridge

• Assault Rifles and their Ammunition: History and Perspectives