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.
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 . "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". 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., vs 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. 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 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. 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 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. The
US Army conducted testing of
telescoped ammunition,
polymer-cased ammunition, and
caseless ammunition for future service cartridges. As of 2022, the candidate for
US Army universal cartridge is the
6.8×51mm Common Cartridge, selected by the US
Next Generation Squad Weapon Program. This cartridge has a muzzle energy even higher than
7.62×51mm NATO. ==Characteristics==