The Search for the Optimum Military Rifle & Machine Gun Cartridge
By Anthony G. Williams

The most successful military rifle and machine gun cartridges in service during the first four decades of the 20th century were powerful rounds of 7.5-8mm (.30-.32) caliber, with effective ranges of well over 1,000 yards. The U.S. .30-06, British .303, German 7.92x57 and Russian 7.62x54R are among the most famous and long-lasting, with the Russian round still being in service.

As early as World War I it had been realised by some observers that such long range performance was unnecessary for most infantry combat, and resulted in rifles which were excessively long and heavy and had too much recoil. However, the need to preserve the capability for long-range machine gun fire, plus military conservatism, combined to retain the status quo until late in World War II.

Experiments with less powerful cartridges were made in several nations in the 1920s and 1930s (notably in the USA with the .276 Pedersen), but it took the stimulus of war to prompt the adoption of the first of these to see service: the German 7.92x33 Kurz used in the MP 43/44/StG 44 selective-fire assault rifle. Captured examples inspired the Russians to develop the 7.62x39 M1943 round used in the Kalashnikov assault rifles and light machine guns. These rounds were not intended to replace the old high-powered cartridges, but to supplement them.

Instead of following suit, NATO countries started an apparently never-ending argument over the optimum characteristics of military rifle and machine gun ammunition. This article is intended to outline the history of this debate, which has been revived as a result of the conflict in Afghanistan.

The NATO Cartridge Trials of 1950

In the late 1940s it was decided to develop one standard rifle/MG cartridge for the new NATO alliance. There was immediately a serious disagreement over the caliber between Britain, Belgian and Canada on one side and the USA on the other. Britain and Belgium had been developing an intermediate round which, while still long-ranging, was smaller and less powerful than the old full-power cartridges. This was the .280 (7x43) which fired a 140-grain bullet at 2,415 fps. The .280 caliber (actually 7mm, with a .276 inch bore and .284 bullet) was a little larger than was thought ideal but was selected to meet American demands for long-range performance.

The USA had also been planning the replacement of the .30-06 cartridge and had developed the concept of a selective-fire “.30 Caliber Lightweight Rifle.” What they really wanted was the automatic .30 M2 Carbine but with the hitting power of the .30 Garand, at a weight of 7 pounds. It was intended to use a shorter cartridge than the .30-06, but was still required to have “a stopping and wounding power which shall not be less than that of the standard caliber .30 ammunition fired from the M1 at ranges of 400, 800, 1,200 and 2,000 yards.” The Americans accordingly ended up with what was simply a shortened version of the .30-06 with a very similar performance.

Comparative trials of the .280 and the new U.S. .30 cal (the T65) were held at Fort Benning in 1950. The .280 generally performed better, its lighter recoil making it more controllable in automatic fire, but the U.S. Army insisted on the adoption of its .30 cal. There was a major argument, the British even going so far as to formally adopt their own cartridge in August 1951 as the 7mm Mk 1Z, but it was never to enter service, being cancelled following American political pressure. Various efforts were made by the .280 supporters to increase the velocity of their ammunition, but in vain; NATO adopted a slightly modified T65 .30 cal cartridge as the 7.62x51.

The Hall and Hitchman Reports, Project SALVO and the SPIW

While the .30 caliber rifle and ammunition were still being developed, some American researchers were coming to different conclusions about the requirements for a military rifle. In 1950 the Ballistic Research Laboratory (BRL), an Army unit based at the Aberdeen Proving Grounds, was asked to investigate combat rifle effectiveness. The resulting report titled An Effectiveness Study of the Infantry Rifle was presented by its author, Donald Hall, in 1952. This was a theoretical study of the effectiveness of different calibres, which concluded that significant improvements in hit probability could be expected of a small-caliber, high velocity cartridge due to its flatter trajectory, and that there would also be benefits in a considerable reduction in ammunition weight.

In parallel with this study, the civilian Operational Research Office (ORO) of the U.S. Army’s General Staff examined what really happened in rifle combat. The resulting report on Project BALANCE by Norman Hitchman, the head of ORO’s Infantry Division, also emerged in 1952. Hitchman’s report was based on World War II combat records plus new data emerging from Korea. This showed that the average distance for aimed bullet hits was in the region of 75-100 yards with 80% of effective rifle and LMG fire being reported at ranges of less than 200 yards and 90% at less than 300 yards. Even worse for the Ordnance Department were tests of its .30 cal Lightweight Rifle prototypes which showed that the recoil was far too heavy, leading Hitchman to report that the cartridge was vastly overpowered and that automatic rifle fire was a waste of time and ammunition. This was five years before the selective-fire M14 in 7.62x51 caliber was officially adopted for US Army service.

Another controversial finding in the Hitchman report was that the accuracy of the rifle made no difference to the hit probability, because the typical aiming errors were so huge. This led in 1952 to the establishment of Project SALVO which, as well as studying conventional small-caliber cartridges, investigated a range of exotic ammunition options, including 12-bore shotgun cartridges loaded with 32 ‘ice pick’ projectiles (flechettes), multi-bullet loadings of .30 cal rifle cartridges with either two (Duplex) or three (Triplex) short bullets stacked on top of each other, and single-flechette rounds.

The promise of the flechette, which combined extremely high velocity with light recoil, led to the concept of the Special Purpose Individual Weapon or SPIW. This was the project which the U.S. Army hoped would provide a replacement for the M14, and huge resources were devoted to its protracted development during the 1960s. It would feature not only a burst-fire flechette rifle but also a 40mm repeating grenade launcher.

Four companies produced SPIW prototypes; AAI, Springfield, Winchester, and Harrington & Richardson. When tested in 1964, none proved satisfactory, falling well short of the specification in many respects. Only AAI and Springfield were asked to continue development. In 1966 the survivors were tested again, but the results overall remained very poor. While work continued until 1973, it was all in vain. The weight target proved impossible to meet, and the flechette rounds never achieved the accuracy nor the low cost required.

This was not the end of the flechette concept. This resurfaced in the Advanced Combat Rifle (ACR) tests in the late 1980s, in guns from AAI and Steyr, with other contenders from Colt (duplex bullet 5.56mm loading) and Heckler & Koch (4.7mm caseless G11). None managed the target of doubling the hit probability over the M16. Unconventional plastic-cased and caseless ammunition also feature in the U.S. Army’s current Lightweight Small Arms Technologies project. Time will tell whether this will be any more successful than previous attempts at advanced ammunition technologies.

The Small-Caliber Revolution

The costly failure of the SPIW project provided the opportunity for a much simpler approach. Even before the 1952 Hall report was published, experimenters at Aberdeen’s BRL and Development and Proof Services (D&PS) had been conducting a small caliber, high velocity (SCHV) research programme. Their work, which was used by Hall, focused on the improvements in hit probability which could result from a high-velocity rifle of .22 inch (5.56 mm) or smaller caliber.

From 1952 until 1956, a series of different small-caliber cartridges were developed in Project SALVO, with calibers ranging from .18 to .27 inches in Simplex (single bullet) and Duplex loadings. These experiments resulted in 1957 in a request from the U.S. Continental Army Command to ArmaLite (a division of the Fairchild Engine and Airplane Corporation) for a small caliber, high-velocity rifle. Eugene Stoner, the most famous post-WWII American military gun designer, went to work on the gun and cartridge, ultimately producing the AR-15 rifle designed to fire the new .223 Remington round. After various tests it was recommended in 1959 that the development of the AR-15 should be pursued as a replacement for the 7.62mm rifle - which had been formally adopted for service only two years before.

This did not immediately result in orders from the Army, which wanted the SPIW. The USAF placed the first order in 1960 to replace the .30 M2 Carbine used by their sentries. Adoption by the Army came about almost by accident, due to the cancellation of M14 production and the need to find a “stop gap” weapon to tide the Army over until the arrival of the SPIW. The AR-15 was officially designated M16 and adopted by the USAF in 1964. The US Army simultaneously chose it as a ‘limited standard’ formally adopting the M16A1 in February 1967. The 55-grain ball loading for the .223 Remington became the 5.56mm M193. As a result of the SPIW’s continuing problems, more and more M16 rifles were bought and this “stop gap” gradually became the Army’s new standard rifle. As the long-range performance of the little bullet was poor, the 7.62mm cartridge hung on in service, primarily in machine guns and sniper rifles, but the M14 was also retained by the USN.

For many years 5.56mm weapons were used by the USA (and purchased by various other countries) but not formally adopted by NATO. This changed following trials held between 1977 and 1980 to select a new NATO cartridge to supplement the 7.62x51. It was effectively impossible to propose any general-purpose round which might have replaced the 7.62x51, since only cartridges substantially smaller than the 7.62mm were considered.

These trials resulted in the selection of the 5.56mm as the next NATO cartridge with the designation 5.56x45 NATO. The Belgian SS109 loading (designated M855 in U.S. production) was chosen; this contains a hard steel element near the bullet tip and is heavier at 62-grains. The muzzle velocity is lower but the velocity loss is reduced, providing significantly improved long-range performance and penetration. However, complaints about a lack of terminal effectiveness of the “green tip” M855 have been going on since Somalia in the early 1990s. As a result, some limited use has been made of the MK262 heavy-bullet loading and work on developing more effective bullets continues - the latest example being the MK318.

The British have recently conducted tests of the effectiveness of 5.56mm ammunition and have determined that it is highly dependent on the impact velocity, which is directly linked to barrel length. The standard L85A2 rifle (20 inch barrel) has been found to have an effective range of 300 metres, while the L110 Para Minimi (about 14 inches - similar to the M4 Carbine) is only effective to 200 metres. Furthermore, experience in Afghanistan has revealed that 5.56mm bullets have negligible suppressive effect. Finally, U.S. experiments have revealed that 5.56mm bullets have poor barrier penetration and also sometimes fail to yaw on impact, inflicting only minor injuries. These findings provide ammunition to those who believe that the 5.56mm is fundamentally too small, and argue for a larger and more powerful cartridge.

The Search for the Optimum Caliber

An attempt to design an optimum military rifle round took place in the UK around 1970. The preferred solution was in 6.25mm caliber, firing a bullet of 100-grains at 2,680 fps. Tests revealed that this matched the 7.62x51 in penetration out to 600 meters and remained effective for a considerably longer distance, while producing recoil closer to the 5.56x45. However, the increasing use of the 5.56mm round meant that the 6.25mm stood no chance of being selected by NATO.

Immediately after the British 6.25mm experiments, the U.S. Army identified a need for an LMG cartridge which could reach out further than the 5.56mm M193. Various experiments resulted in the 6x45 SAW (Squad Automatic Weapon) which fired a relatively heavy 105-grain bullet at a velocity of 2,520 fps for optimum long-range performance. The SAW was abandoned in favour of the promised long-range loading for the 5.56x45 (which eventually arrived as the M855) and because fielding two similar calibers at squad level was felt to be inefficient.

Since 2000, two new attempts at a better rifle cartridge have been made. First on the scene was the 6.8x43 Remington SPC (Special Purpose Cartridge), which was a joint effort between Remington and a group within USSOCOM. After testing various calibers they settled on 6.8mm as having the best blend of characteristics. The 6.8x43 typically fires a 115-grain bullet at 2,590 fps. It not only demonstrates far superior terminal effectiveness and barrier penetration than the 5.56mm at short range; its advantage increases with range.

The other new cartridge is the 6.5x38 Grendel. Normally firing a 123-grain bullet at around 2,520 fps, this matches the 6.8mm in power but the heavier, more aerodynamic bullet matches the energy delivered by the 7.62mm M80 ball at long range, offering the potential to replace the 7.62x51 as well as the 5.56x45. Weight, power and recoil of these new cartridges are both roughly midway between the two existing service rounds.

Recent experience of asymmetric warfare in Afghanistan has re-emphasised the importance of effective small-arms fire, and at much longer ranges than expected. A British Army study has shown that more than half of all small-arms attacks by the Taliban (using weapons in 7.62x54R caliber such as the Russian PKM LMG) take place at between 300 and 900 metres. That is beyond the effective range of 5.56 mm weapons and has led to the allocation of 7.62mm machine guns and even sniper rifles to foot patrols, despite the unwelcome extra weight of guns and ammunition.

Over the next decade several NATO countries will be selecting new rifles, including the USA and the UK. This provides a rare opportunity to reconsider the ammunition they will be using. The ability of cartridges in the 6.5-7mm range to greatly improve on the 5.56mm, plus match the long-range performance of the 7.62mm with less weight and recoil, combine to make a strong case for one new, general-purpose rifle/MG round. Will the opportunity be seized this time? Watch this space!

(Anthony G Williams is an independent consultant, co-editor of Jane’s Ammunition Handbook, and co-author with Maxim Popenker of “Assault Rifle: the Development of the Modern Military Rifle and its Ammunition.” He maintains a website at www.quarry.nildram.co.uk)

This article first appeared in Small Arms Review V13N7 (April 2010)
and was posted online on April 13, 2012


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