Intermediate cartridge
An intermediate cartridge is a rifle/carbine cartridge that has significantly greater power than a pistol/personal defense weapon cartridge but still has a reduced muzzle energy compared to fully powered cartridges (such as the  .303 British, 7.62×54mmR, 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 calibers.

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 , 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.

Early intermediate cartridges to see service were 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 and AK-47 rifles) and 5.45×39mm M74 (used in the AK-74, which replaced the AK-47), the Belgian SS109 / 5.56×45mm NATO (used in most AR-15 Systems), and the Chinese 5.8×42mm (used in the QBZ-95 family of rifles).

History

High power rounds
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 , and they were longer than  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  for simultaneous fire at distant area targets like ranks of enemies, but typical combat ranges were much shorter, around , rarely exceeding .

Overpowered
During World War II, to improve close combat ability, some semi-automatic rifles were created, such as the American M1 Garand, Soviet SVT-40 and the German Gewehr 43. These semi-automatic rifles offered a significant advantage in firepower and shot-to-shot recovery time over enemy infantrymen armed primarily with similar chambered bolt-action rifles. For close quarter combat, a more common solution was the submachine gun. Weapons such as the Soviet PPSh-41 and PPS-43, 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 a study on the M1 Garand's fire rate; a trained soldier averaged 40–50 accurate shots per minute at a range of . "At ranges over , a battlefield target is hard for the average rifleman to hit. Therefore,  is considered the maximum effective range, even though the rifle is accurate at much greater ranges".

Lighter rounds
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.

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. 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.

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 their 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. The British EM-2 bullpup 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 they were 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.

Since that time, there has been a worldwide move to rounds of roughly the same performance as the .223 Remington. The Soviets introduced their 5.45×39mm in 1974, another round of NATO standardization led to the improved .223 5.56×45mm NATO in 1980, and the Chinese 5.8×42mm in 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.

Universal service cartridge
Some militaries have considered 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 caliber to 7mm caliber caliber range, with external and terminal ballistic performance close or equal to the 7.62×51mm NATO and 7.62×54mmR full-power cartridges. The .280 British (7×43mm) and Czech 7.62×45mm were early attempts to create universal service cartridges. The US Army conducted testing of telescoped ammunition, polymer-cased ammunition and caseless ammunition for future service cartridges. The viability of a universal service cartridge has been criticised, and as of 2020, no intermediate cartridge has been replaced.

Characteristics
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  Pmax piezo pressure
 muzzle energies ranging between 
 Muzzle velocities ranging between 
 Relatively low Oratios ranging between 2.87 and 7.99

List of intermediate cartridges

Service cartridges
Service cartridges are cartridges the service rifles of armies were or are chambered for.
5.45×39mm cartridge of the AK-74 assault rifle
5.56×45mm NATO (.223 Remington) of the M16 assault rifle and M4 carbine
5.8×42mm cartridge of the QBZ-95 assault rifle
.30 Carbine (7.62×33mm) cartridge of the US M2 select fire carbine and M1 semi-automatic carbine
7.62×39mm cartridge of the AK-47 assault rifle and  SKS semi-automatic carbine
7.62×45mm cartridge of the vz. 52 semi-automatic rifle
7.92×33mm Kurz cartridge of the StG 44 assault rifle

Prototype cartridges

4.85×49mm cartridge of the experimental Enfield IW assault rifle
6×45mm SAW cartridge of the experimental Rodman Laboratories XM235 light machine gun, a project which terminated in the M249
6.5×39mm cartridge based on the 7.62×39mm of variants of the AR-15 and Zastava M70 assault rifles
6.8mm Remington SPC (6.8×43mm) cartridge of the limited service LWRC M6 assault rifle
.280 British (7×43mm) cartridge of experimental weapons and the briefly in  service EM-2 assault rifle
7.5×38mm chambered for the CEAM Modèle 1950 rifle and experimental French variant of StG 45(M) 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 chambered in CEAM Modèle 1950 and experimental French variant of the StG 45(M) rifle
7.75×39mm GeCo the first intermediate round ever made, German experiment
12.7×55mm STs-130 subsonic cartridge of the limited service ShAK-12 assault/battle rifle

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

References

External links
 Assault Rifles and their Ammunition: History and Perspectives

Cartridge families