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An intermediate cartridge is a firearm cartridge that is less powerful than typical full-power battle rifle cartridges, such as the United Kingdom .303 British, Russian 7.62×54mmR, German 7.92×57mm Mauser or United States .30-06 Springfield, but still has significantly longer effective range than pistol cartridges. As their recoil is significantly reduced compared to high power rifle cartridges, fully automatic rifles firing intermediate cartridges are relatively easy to control. However, even though less powerful than a traditional rifle cartridge, the ballistics are still sufficient for an effective range of 250–500 metres (270–550 yd), which are the maximum typical engagement ranges in modern combat. This allowed for the development of the assault rifle, a selective fire weapon that is more compact and lighter than rifles that fire full power cartridges. The first intermediate cartridge to see widespread service was the German 7.92×33mm Kurz used in the StG 44. Other examples include the Soviet 7.62×39mm used in the AK-47 and AKM series, and the .280 British round developed for the EM-2. The 5.56×45mm NATO cartridge is also an intermediate cartridge.
The Second World War saw the use of the bolt-action rifles such as the Mauser Karabiner 98k, the Lee–Enfield SMLE, the Mosin–Nagant, the Arisaka Type 38, and Type 99 rifles, and during the early years, the Springfield M1903, as well as semi-automatic battle rifles such as the Gewehr 43, the M1 Garand, and the SVT-40. These rifles weighed over 8 lb (3.6 kg), and they were longer than 40 in (1,000 mm) and as such inappropriate for close combat. They fired cartridges capable of killing out to 1,000 m (1,100 yd). In close quarter combat, all the major armies began employing submachine guns such as the PPSh-41, Thompson M1928A1, and the MP-40, all of which fired pistol cartridges. Compared with the battle rifles, these submachine guns could provide high rates of controllable fire, but they lacked the power and longer effective range of the battle rifles.
Bolt-action rifles in use at the time were long and heavy, and their rate of fire was only around 10 - 15 rounds per minute. The bolt-action rifles were effective up to 800–1,000 metres (870–1,090 yd) in the hands of a trained marksman, but typical combat ranges were much shorter, around 150–300 metres (160–330 yd), rarely exceeding 500 metres (550 yd). Therefore, the potential of the 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
What was needed was a more compact, selective fire weapon firing a cartridge combining the power of a rifle and the controllability of pistol cartridges. The resulting cartridge would have the accuracy of the former for typical combat ranges, and the firepower of the latter at short ranges.
The first cartridge fulfilling this requirement may have been the Japanese 6.5×50mm Arisaka used by the Russian Fedorov Avtomat rifle since 1915 (the cartridge itself dates back to 1897). The Fedorov was arguably the first assault rifle. Later came the US .30 Carbine, developed as a weapon for officers and rear area soldiers unlikely to be involved in infantry assault, but needing 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 another candidate for first assault rifle, the StG-44. When the Soviets developed the AK-47, they already had an intermediate cartridge of their own, so they adopted the gas operation system of the StG-44, which was extremely reliable.
Since the 1960s 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 5.56×45mm NATO, Soviet 5.45×39mm, and Chinese 5.8×42mm. These intermediate cartridges allow a soldier to carry more ammunition for the same weight compared to their larger and heavier predecessor cartridges and produce relatively low bolt thrust and free recoil impulse, favouring light weight arms design and automatic fire accuracy.
Typical intermediate cartridges have:
- Cartridge case capacities ranging between 1.75–2.79 ml (27.0–43.1 grains H2O)
- 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) Pmax piezo pressure
- Bullet weights ranging between 3–9 g (46–139 gr)
- muzzle energies ranging between 1,328–2,717 J (979–2,004 ft·lbf)
- Muzzle velocities ranging between 685–940 m/s (2,247–3,084 ft/s)
- List of assault rifles
- 4.85×49mm Chambered for Enfield IW assault rifle which led to the development of the SA80 series firearms
- 5.45×39mm cartridge of the AK-74 assault rifle
- 5.56×45mm NATO cartridge of the M16 assault rifle
- 5.8×42mm DBP87 cartridge of the QBZ-95 assault rifle
- 6.5×39mm 6.5 mm Grendel cartidge developed for AR-15
- 6.8×43mm 6.8 mm Remington SPC cartridge
- 7.2x43mm (.280 British) cartridge of the EM-2 assault rifle
- 7.5×38mm chambered for the CEAM Modèle 1950 rifle
- 7.62×39mm cartridge of the AK-47 assault rifle
- 7.62×45mm cartridge of the vz. 52 semi-automatic rifle
- 7.65×33mm Argentine variant of German 7.92×33mm cartridge for use in Argentine copy of German Sturmgewehr 44 assault rifle
- 7.65×35mm French chambered in experimental French variant of StG 45(M) rifle
- 7.75×39mm GeCo the first intermediate round ever made, German experiment
- 7.92×33mm cartridge of the Sturmgewehr 44 assault rifle
- Table of handgun and rifle cartridges
- Bull, Stephen (2004). Encyclopedia of Military Technology and Innovation. Greenwood. p. 25. ISBN 978-1-57356-557-8.
- Hogg, Ian V. (1983). Modern Small Arms. United Kingdom: Bison Books Ltd. p. 136. ISBN 978-1-85841-075-3.
- Williams, Anthony (6 Feb 2012). "Assault Rifles and their Ammunition: History and Prospects". Retrieved 4 Apr 2012.
- Болотин, Давид (1995). "Глава 5. Автомат Фёдорова и унификация стрелкового оружия на его базе" (PDF). История советского стрелкового оружия и патронов (PDF) (in Russian). СПб.: Полигон. pp. 156–165. ISBN 5-85503-072-5.
- Assault Rifles and Their Ammunition: History and Prospects by Anthony G. Williams