The AAI Corporation was founded in 1950, as Aircraft Armaments, Inc., and has long been involved in advanced firearms design, taking part in a number of the US military’s previous small arms programs. Throughout the Cold war AAI was involved in the US Army’s search for a new advanced infantry weapon system. Before we examine the AAI ACR, it is important to understand the context in which it evolved.
The Special Purpose Individual Weapon (SPIW) program, an off-shoot of Project SALVO began in the early 1950s and ran until the late 1960s. During the SPIW program AAI developed a series of designs, including an entire family of weapons, which used flechette technology. These culminated with the XM19 rifle, or SFR – Serial Flechette Rifle. The XM19 represented the pinnacle of over a decade of flechette technology development, however, the end of the US war in Vietnam saw the need for SPIW disappear and the program was wound down.
In the early 1970s SPIW essentially morphed into the Future Rifle Program, but with the end of US involvement in Vietnam, this also proved a failure. During the early 1980s the US Army awarded development contracts to both AAI and Heckler & Koch to develop caseless ammunition and a weapon system capable of firing it. While H&K G11 is no doubt the better known of the two weapons, AAI’s Caseless Weapon, while a move away from flechette technology, was also an interesting design.
Firing a variety of ammunition the AAI design was capable of firing a high cyclic rate 3-round burst at 1600-1800rpm. The ACR program summary report noted that the AAI Caseless project was feasible and only lacked development funding to make it a reality, as the design was much simpler than the G11.
AAI were one of six companies to respond to the ACR program’s Request for Proposals, released in September 1985. AAI’s ACR was an evolution of the earlier SFR/XM19 rifle. The weapon AAI submitted was gas-operated, fed from a 30-round box magazine, and fired a brass cased flechette round in either single shot or a high cyclic rate three round bust – fired at a cyclic rate of ~1800rpm.
AAI’s ACR fired from a closed bolt and used a muzzle device to reduce muzzle climb during burst firing. The 1990 ACR Program Summary report explains how the rifle’s gas system worked:
“…incorporate an ‘entrapped gas’ operating system. Gun gases enter a cylinder, drive a piston to power the system, and prevent any leakage of propellant gases and residues into the other mechanism parts.”
AAI developed a polymer saboted steel 10.2 gr ‘sub-calibre’ flechette which fitted within a standard M855 brass case. As a result the rifle used a proprietary magazine to avoid the accidental chambering of conventional 5.56x45mm rounds. The flechette rounds had a muzzle velocity of 4,600 ft/s with propellant produced by the Olin Corporation.
The rifle was designed to mount a quick detachable 4x optic and also had a white-highlighted shotgun-style rib sight along the barrel to aid snap shooting. The rifle was one of the longest entries with an overall length of 40 inches or 101.6cm. Interestingly, rather than a push-button magazine release, AAI opted for a large paddle release.
AAI’s rifle borrowed some of its external ergonomic characteristics from the M16A2, then in service. With a moulded polymer pistol grip and butt, forming part of the lower receiver, shaped to mimic the M16’s. It also utilised the M16’s sling loops and butt plate.
According to the ACR program summary the AAI entry proved to be a “mature design which performed in a reliable fashion” during the field trials. It was regarded as a weapon with known reliability with a flechette round superior to the Steyr, the other flechette-based entry.
Today, AAI continue to develop both small arms and other defence technologies. Now a part of Textron, they are currently involved in the US Army’s Lightweight Small Arms Technologies (LSAT) program.
Specifications (From 1990 ACR Program Summary):
Length: 40 inches / 101.6cm
Weight: 9.39 lbs / 4.26kg
Sights: Iron or 4x optic
Action: Gas operated
Calibre: 5.56mm brass cased flechette
Feed: 30-round box magazine
You can find out overview article on the ACR program and all of the rifle here.
Advanced Combat Rifle, Program Summary, Vol.1, ARDEC, 1992 (source)
‘Revisiting the SPIW Pt. 1-3’, Small Arms Review, R. Blake Stevens, (123)
The SPIW The Deadliest Weapon that Never Was, R. Blake Stevens & E.C. Ezell (1985)
Our thanks to the collection that holds these wonderful examples of the ACR rifles
With so few primary or secondary sources on the ACR program available, this article relies heavily on the 1990 program summary report written by the US Army Armament Research, Development and Engineering Center (ARDEC). Over the next three articles we will examine the AAI, Colt and Steyr ACR entries. The H&K entry was covered earlier – here.
In the early 1980s the US Army began looking into what form a replacement for the M16A1 might take. The Joint Service Small Arms Program undertook a study and found that in the long term a “technology base should be developed to support a significant improvement in capability.” This meant the US infantryman’s next rifle would move away from conventional ammunition and actions.
The Advanced Combat Rifle program began in January 1985, to foster the development and select a rifle that would give troops a distinct advantage on the battlefield. The project’s ambitious aim was to address the human shortcomings of the average soldier in the field. It was found that combat stress, fear and fatigue negatively impacted on a rifleman’s ability to hit a target once engaged in combat.
The ACR program sought to compensate for this by maximising hit probability when engaging fleeting targets in battlefield conditions. The program called for:
“an enhancement in hit probability of at least 100 percent at combat ranges over the baseline performance of the M16A2 rifle… at extended ranges, the improvement required will be considerably greater than 100 percent. The weapon will be expected to enable the rifleman to detect rargets at ranges greater than 400m in offensive action and at least 1000m during the conduct of the defense.”
This was a tall order, calling for a weapon with an optic and the ability to engage long range targets, which were envisaged to be wearing body armour, but also engage fleeting targets. But the ACR program was far from the US military’ first ambitious small arms project.
The ACR program built on the Special Purpose Individual Weapon (SPIW) program that had been established in the 1950s to produce the next generation of infantry weapon capable of firing busts of flechettes at extremely high rates of fire to improve hit probability. This task proved technologically insurmountable during the 1950s and 60s. The SPIW program ended in the late 1960s, but was followed in the early 1970s by the Future Rifle Program which also proved a failure. Despite these failures the programs helped to push small arms technological boundaries.
In the video below, produced by ARDEC for the US Department of Defence, we see the ACR program briefly explained and the various rifles introduced with some firing footage:
The approaches used by the companies that entered the ACR competition varied greatly. Ranging from rifles with complex buffer systems to weapons that fired duplex and flechette rounds.
The first Request for Proposals was released in September 1985, with six companies successfully submitting proposals. These companies, which were awarded a Phase I contract, were: AAI Corporation, Ares Incorporated, Colt’s Manufacturing Company, Heckler & Koch (H&K), McDonnell Douglas Helicopter Systems (MDHS), and Steyr Mannlicher. In 1987, following Phase I of the program the entries from Ares and MDHS were dropped due to ‘hardware immaturity’ – the concepts were not developed enough. Both companies appealed and were allowed to enter designs to Phase II but neither was sufficiently developed to compete in the later trials and testing.
Each company approached the program’s aims in a different way. Two utilised flechette technology, which had been developed during the SPIW program, with the AAI using a brass cased round while the Steyr ACR used a polymer case. Colt’s entry used a duplex round with two projectiles stacked in the cartridge case. Heckler & Koch’s G11 used a complex buffer system to reduce felt recoil after firing a ‘hyper burst’ of three rounds at ~2,000 rounds per minute.
Lets take a look at the individual weapon systems:
AAI Corporation had long been involved in advanced firearms design, taking part in the US military’s previous programs. The AAI ACR was an evolution of the earlier SFR/XM19 rifle. AAI’s ACR was gas-operated, feeding from a 30 round box magazine and fired a brass cased flechette round in either single shot or a high cyclic rate three round bust.
It fired from a closed bolt and used a muzzle device to reduce muzzle climb during burst fire. AAI developed a polymer saboted steel 10.2 gr flechette which fitted within a standard M855 brass case. As a result the rifle uses a proprietary magazine to avoid the accidental chambering of conventional 5.56x45mm rounds. These rounds had a muzzle velocity of 4,600 ft/s.
The rifle was designed to mount a quick detachable 4x optic and had a white-highlighted shotgun-style rib sight along the barrel to aid in snap shooting. The rifle was one of the longest entries with an overall length of 40 inches or 101.6cm.
According to the ACR program summary the AAI entry proved to be a “mature design which performed in a reliable fashion” during the field trials.
Specifications (From ACR Program Summary):
Length: 40 inches / 101.6cm
Weight: 9.39 lbs / 4.26kg
Sights: Iron or 4x optic
Action: Gas operated
Calibre: 5.56mm brass cased flechette
Feed: 30-round box magazine
Colt’s Manufacturing Company
Check out Vic’s video on the Colt ACR and an article with further detail here [Coming soon]
Colt’s entry was perhaps the most conventional of the designs submitted. Based on the rifle the program sought to replace. Colt’s ACR was essentially an improved M16, which fired both conventional 5.56x45mm ammunition as well as a new 5.56mm duplex round. While the duplex round increase hit probability at shorter ranges, it impacted long range accuracy requiring the additional use of conventional M855 rounds.
It incorporated a variety of improvements including a new oil/spring hydraulic buffer to mitigate recoil. A reshaped pistol grip and a hand guard which mounted a sighting rib for snap shooting. The weapon had a flat-top upper receiver which was railed so a 3.5x optic (an early ECLAN) or a more conventional sight/carrying handle could be fitted.
The rifle’s collapsible six position telescopic butt stock was an improved version of that offered with Colt’s carbines. When at full extension the Colt ACR was the longest rifle tested, at 40.6 inch or 103 cm long. A distinctive proprietary muzzle brake compensator designed by Knight’s Armament was also added.
During testing one of the duplex rounds was not properly seated inside the cartridge case and when fired became lodged in the barrel and during the course of fire and the weapon’s barrel blew when another round was fired. This was addressed by a slightly larger propellant charge. Some of the features developed for the ACR entry were later employed in the M16A3 and later A4.
Specifications (From ACR Program Summary):
Length: 40.6 inches / 103cm (extended) and 36.7 inches / 93.2cm (collapsed)
Weight: 10.3 lbs / 4.67kg
Sights: iron or 3.5x optic
Action: Direct gas impingement
Calibre: 5.56mm duplex round & M855 ball
Feed: 30-round box magazine
Heckler & Koch had been involved in the West German Bundeswher’s attempts to create a next generation infantry weapon. The result was the G11, the G11 had been in development since the late 1960s and by the time it was entered into the ACR program it had evolved into a complex weapon unlike any other. Utilising a gas-operated, rotary breech to fire self-contained caseless 4.73×33mm projectiles. The rotary breech chamber was introduced as a means of clearing misfired, broken or defective cartridges from the enclosed system. Simplicity was sacrificed to achieve reliability.
The US had awarded H&K a contract to develop caseless ammunition, optics and the salvo concept in 1982. With the G11 in development they then entered the ACR program. The bullpup H&K was the shortest of the weapons entered into the trial at 29.5 inches / 74.9cm. It was equipped by a variable 1-3.5x optic designed by Swarovski.
The revolutionary ammunition was developed by Dynamit-Nobel AG.
The 4.73x33mm, 51gr round which was finalised comprised of a solid propellant material body which encased a primer, booster, projectile and a plastic nose cap. Dynamit-Nobel developed the High Ignition Temperature Propellant (HITP) in an effort to prevent accidental ignition (cook-off) of the ammunition’s outer propellant body. The ACR program summary notes that “the majority of the malfunctions/stoppages experience in the field experiment were ammunition related.”
The H&K ACR fed from a single stack, horizontally orientated 45-round magazine which sat above the barrel.
The G11 used a counter-recoil buffer mechanism to allow high rates of burst fire – hyper burst. When firing three round bursts the weapon could send the rounds downrange at a rate of ~2,000 rounds per minute, only when the last round has left the barrel does the barrel and action begin to recoil inside the stock along a central guide. The recoil impulse was then quite strong. When in sustained fire the rate of fire is closer to ~460 per minute. A more detailed explanation of the G11’s action can be found here.
Check out Vic’s video on the Steyr ACR and an article with further detail here [Coming soon]
Steyr-Mannlicher’s bullpup entry uses a gas piston driven rising chamber mechanism which rises and falls to chamber rounds as the action cycles. The Steyr ACR, like AAI’s entry, fires flechettes but Steyr’s are housed inside a cylindrical polymer case. The bullpup Steyr was the second shortest at 30 inches (76cm) and the lightest of the rifles submitted weighing 8.5 lbs (3.86kg).
The Steyr ACR borrows its ergonomics from its conventional forebearer, the AUG. With a moulded green plastic stock and a similar pistol grip, trigger and safety layout. Unlike the AUG, however, the ACR uses an AR-15 style charging handle located at the rear of the sight mounting block. The rifle could be fitted with a variable 1-3.5x optic.
The rifle does not use a conventional bolt, instead it has a rising chamber, as a result the rifle fired from an open bolt. A live round only entered the chamber after the trigger had been pulled, thus reducing the potential for cook-offs. Spent polymer cases were pushed out of the chamber and ejected from an opening just in front of the magazine well.
Feeding from a 24-round box magazine, made from the same translucent material used in conventional AUG magazines. The magazine goes from double stack to single stack, to allow it to feed reliably, as a result the capacity had to be shortened. A high capacity drum magazine was planned but not provided for the trials. The polymer case held a fin stabilised 9.85 gr flechette with a moulded four piece sabot which broke up soon after exiting the muzzle. This was identified as a shortcoming as it risked hitting nearby troops.
After several years of development, while the Army organised testing, the four firms delivered their prototypes in 1990. During Phase III the rifles were tested on the specially built Buckner Range – designed to recreate field conditions and create fleeting targets at various ranges. The M16A2 was used as a baseline weapon throughout all of the tests which included safety and engineering testing, lethality tests and testing in field conditions.
Initially planned as an all-services test both the US Navy and Marine Corps pulled out of the ACR program in 1987, leaving the Army and Air Force. With the testing complete it was found that none of the rifles proved to be significantly more lethal or effective than the M16A2 they were pitted against. The program summary put a rather positive spin on the program’s failings, concluding that despite the increased hit probabilities not being attained as a technology base program, the ACR program was a success. The soldiers taking part in the field tests performed better than expected and “the baseline performance of the M16A2 rifle was better than anticipated in terms of hit probability.”
The report concluded that the program had helped push small arms technology forward, noting that while flechettes proved to be too inaccurate for an individual weapon,
“The feasibility of caseless and lightweight plastic-cased ammunition has more than been demonstrated in this program. Few problems were experienced with the [H&K] caseless rifles in the test. The past technical barriers of cook-off and vulnerability have now been overcome. …plastic cases cannot be used in conventional weapons like the M16A2, but with weapons specifically designed for it, complete plastic cases are feasible.”
With the end of the ACR program the school of thought moved towards the use of high explosive and airburst munitions by individual soldiers. The Objective Individual Combat Weapon program ran throughout the early 1990s and while it lead to the adoption of some new weapons, such as the M320 grenade launcher, it also failed in its goal to create an integrated individual weapon system.
Advanced Combat Rifle, Program Summary, Vol.1, ARDEC, 1992 (source)
‘Revisiting the SPIW Pt.3’, Small Arms Review, R. Blake Stevens, (source)
Our thanks to the collection that holds these wonderful examples of the ACR rifle
In the late 1970s James Sullivan, one of ArmaLite’s former chief designers and one of the men responsible for the M16, began developing a new light machine gun for a company in Singapore. The Ultimax 100 is a 5.56x45mm, gas-operated magazine-fed light machine gun. It uses a short stroke gas piston system that acts on a continuously recoiling bolt.
Sullivan was originally approached to develop a new select-fire intermediate cartridge rifle for the Singaporean military. Working with Chartered Industries he developed a very lightweight light machine gun. Sullivan was especially interested in recoil mitigation and developed the Ultimax’s bolt to travel rearward without ever hitting a buffer or the receiver. This greatly lowers perceived recoil and makes the weapon much flatter shooting.
The Ultimax fires from an open bolt (which uses a multi-lug rotating bolt head) and has a non-reciprocating charging handle. It’s buttstock can be removed to make the weapon even more compact. The absence of a buffer in the butt allows the weapon length to be reduced to just 81cm (32 inches), making it an excellent weapon for jungle or urban combat. The Ultimax is also extremely light for a squad automatic weapon, weighing approximately 4.7kg unloaded, and around 6.5kg when loaded with a 100-round drum.
While the MkII Ultimax has a fixed barrel, the MkIII has a quick change barrel which releases by pulling a catch the the rear and simply twisting the barrel and pulling it forward. Unlike other machine guns the bolt can remain forward when the barrel is being removed.
The Ultimax feeds from either an adapted STANAG magazine or a 100 round drum magazine, which has a controlled internal feed rather than a belt. The drum was co-developed by Sullivan and Bob Waterfield. The weapon’s rear pistol grip is similar to the Stoner 63 weapon system’s (which Sullivan had also worked on) while the smaller, grooved front pistol grip is reminiscent of the classic Thompson submachine gun’s.
It is said that Singapore’s government would not allow the Ultimax to be entered in the US’ Squad Automatic Weapon trials as the US government had refused them the technical package for the M16. As a result the FN Minimi won the trials and was adopted as the M249. Those who have fired both claim that the Ultimax would have given the Minimi more than a run for its money. Despite this the Ultimax has seen action around the world and has been in service with the Singapore Army since 1982.
An updated version was offered in the US Marine Corps’ Infantry Automatic Rifle trial but was beaten by Heckler & Koch’s HK416, now the M27. ST Kinetics, formerly Chartered Industries, continues to improve and produce the Ultimax with the Mk8 introduced in 2012.
Vic brings us the second part of his special episode looking at the story of the AR-10, with a very unique run down of various variants of Eugene Stoner’s weapon. Vic runs us through every production model made by Artillerie Inrichtingen as well as several special prototypes and transitional models.
After a recap look at an example of a Hollywood-made rifle Vic shows us how the AR-10 worked using an instructional cutaway model. Throughout the video Vic examines all of the major production guns, beginning with an early A.I. production gun that incorporates the same ‘beer can’ muzzle device as the original American-made rifles. Vic then takes us through a series of rifles that represent the evolution of the design.
Beginning with the Cuban model, with its pencil profile barrel and top mounted gas tube. This model was also trailed by both the Dutch Army and the German Bundeswehr. Later in the video Vic gives us a quick look at the various German trials rifles the FAL (G1), the SIG 510-1 (G2), the H&K/CETME (G3) and the AR-10 (G4).
Vic follows the Cuban model with a look at the Sudanese Model, with its bayonet lug sleeve, and the Guatemalan variant which swaps out the bayonet lug for rifle grenade launching capability. The Sudanese military ordered 2,508 rifles from A.I.
In addition to these Vic also gives us a look at an extremely rare prototype carbine, a sporter model (the AR-102) and a prototype squad automatic weapon with a heavier profile barrel. Vic then takes us through the features of the final A.I.-made variant, the Portuguese or NATO model. The rifle was officially adopted by the Portuguese army’s Caçadores Páraquedistas (paratroops) and saw action in Angola, Portuguese Guinea and Mozambique.
Vic then takes a look at a series of rare variants and one-offs, including a rifle with green furniture made for Prince Bernhard, the Royal consort to Queen Juliana of the Netherlands, and a heavy barrelled magazine-fed squad automatic rifle with a rubber butt-pad and additional folding carrying handle.
To round out the story of Artillerie Inrichtingen’s involvement with the AR-10, Vic is lucky enough to take a close look at an M1 Garand adapted to feed from surplus AR-10 aluminium waffle magazines. This concept was developed to equip the NATRES, the Dutch Army Reserve, and was based somewhat on the Italian Beretta BM-59. Vic shows us both a very early prototype BM-59 and one of only two A.I. Garand adaptation prototypes.
In this first part of a TAB special episode examining the history of the ArmaLite AR-10 Vic discusses the early origins, history and development of the now legendary 7.62x51mm rifle. At the heart of this episode is a remastered version (certainly the best currently available online) of the c.1958 ArmaLite/Fairchild promotional film that features Eugene Stoner and shows many of the early ‘Hollywood’ Armalites in action! The first part of this special documentary concludes with Vic examining a Hollywood-made AR-10B (the last iteration of the US-made AR-10s).
Much has been written about the AR-10, Eugene Stoner and the genesis of the AR-15’s parent rifle. It’s a design which owes much to many: Stoner, George Sullivan, Melvin Johnson and later the engineers at Artillerie Inrichtingen.
ArmaLite, formed by George Sullivan with the help of Richard Boutelle, President of the Fairchild Engine and Aircraft Corporation, began work on the first AR-10 prototypes in 1955. Designed by Eugene Stoner, using his patented direct gas impingement system. Stoner patented this system in 1956, with the patent being granted in September 1960 (US #2,951,424).
The AR-10 had an aluminium-alloy forged receiver, an in-line stock, polymer furniture and chrome-lined steel parts. While conventional steel barrels were the norm an ill-fated attempt to use an aluminium/steel composite barrel during US Army evaluations proved disastrous when the steel inner parted from the aluminium outer and caused the barrel to burst. As a result of these weight saving efforts the rifle weighed just ~3.4kgs/7.5lbs unloaded. The Armalite AR-10 had a side mounted gas tube, a top mounted charging handle and fed from 20-round box magazines. One of the most interesting features was the large aluminium muzzle device, fitted to some ArmaLite-made Rifles, which reduced sound and flash.
In 1957, ArmaLite sold the AR-10 manufacturing rights to the Dutch small arms manufacturer Artillerie Inrichtingen, while US manufacture was licensed by Colt in February 1959. With minimal financial returns Fairchild sold their interests in ArmaLite in 1962.
Featured in the first part of Vic’s special episode on the AR-10 is an original Armalite/Fairchild promotional film, originally filmed in 16mm, that dates from around 1958. While a version of this film has been shared online for a number of years it is grainy, washed out and of relatively low audio quality. Vic reproduced the very rare promotional sales film in the 1990s onto VHS (a process he explains in the video). He has managed to take an original VHS copy and digitally remaster it to regain some of the original’s clarity and detail.
The promotional film was originally used by salesmen to showcase the AR-10 to potential clients and features Hollywood-produced guns. Both Stoner and Charles Dorchester (ArmaLite’s production manager) are seen in the film demonstrating the AR-10. The rifle’s action, function and controls are explained and various variants, including rifle and light machine gun, are demonstrated. The demonstration segment included a sub-zero test, covering in sand and much and Stoner himself dumping 5 magazine’s through the rifle in quick succession. The promotional film concluded with demonstrations of firing rifle grenades and a belt-fed AR-10.
Vic concludes the first part of the AR-10 overview episode with an examination of an AR-10B rifle held by the Netherlands’ Nationaal Militair Museum. In the second part of the episode Vic will look at nearly a dozen AR-10 variants made by Artillerie Inrichtingen (A.I.) between 1957 and 1961.
Vic kicks off his series looking at the US Army’s ACR trials rifles with a look at, not one but two versions of, Heckler & Koch’s advanced caseless ammunition assault rifle – the G11. This video is an introductory overview, we’ll be delving into the G11’s insanely intricate and wonderfully complex action in later videos!
There are few experimental weapons that have cultivated myth and reputation like Heckler & Koch’s G11. The product of decades of research and development into what was hoped would be the next evolutionary step in small arms design. The G11 was Germany’s attempt to combine advanced caseless ammunition with a weapon system which could increase the average infantryman’s hit probability. The G11’s action has three distinct modes of fire and uses a complex action and buffer/recoil system to achieve a high rate of controlled fire.
The program began in the late 1960s as part of a NATO initiative, however, it became a primarily Bundeswehr project and over two decades the design evolved substantially. The project sought to increase the hit probability of the individual infantryman. Heckler & Koch’s approach to this problem was the most radical. Working with Hensoldt to develop an integrated optical sight and with Dynamit-Nobel to create a new kind of ammunition.
Numerous studies and theoretical designs were worked up but by the mid-1970s the base design of what would become the G11 was cemented. The design team included Gunter Kastner, Dieter Ketterer, Tilo Moller and Ernst Wossner – all of whom are credited in H&K’s 1976 patent protecting the G11’s rotary action.
The G11 went through dozens of iterations throughout the 1970s and 80s, with the first firing prototypes ready by 1974. Both the design and the ammunition also went through a number of changes.
The revolutionary ammunition was developed by Dynamit-Nobel AG.
The 4.73x33mm round which was finalised comprised of a solid propellant material body which encased a primer, booster, projectile and a plastic nose cap. Dynamit-Nobel developed the High Ignition Temperature Propellant (HITP) in an effort to prevent accidental ignition (cook-off) of the ammunition’s outer propellant body.
The G11 fed from 45 or 50-round horizontal, single stack box magazines which fed rounds into the action at 90-degrees. The rounds were then rotated into alignment with the breech by the rifle’s action.
The rectangular shape of the Dynamit-Nobel ammunition was more efficient and better suited to storage than conventional circular rounds. The positioning of the magazine along the top of the weapon, parallel to the barrel, also in theory helped minimise the rifle’s profile and reduce encumbrance for the soldier equipped with the weapon.
The G11 is a gas-operated weapon with gas being tapped from the barrel, to cycle the rifle’s cylinder drive system, which rotated the breech through a series of cams and gears. At the heart of the G11 is a complex rotary action. Rotating actions themselves are not a new concept with the earliest dating back to the 17th century, such as the Lorenzoni system.
The G11’s rotating breech was patented in late 1976 by Heckler & Koch. While our initial video does not go into detail on how the G11 operates, we will be covering this in later videos, this article will explain the action in more general terms.
Below are two diagrams showing the internal layout and major components of the G11 from a March 1982 draft of the ‘Rifle, 4.92mm, ACR’ armourer’s manual (source). It shows the major assembly groups and also a component list for the breech assembly.
From the diagram we can see the various action parts which feed the projectile into the breech, lock the action and ignite the round. We can also see the counter-recoil system beneath the barrel.
The G11 used a counter-recoil buffer mechanism to allow high rates of burst fire. When firing three round bursts the weapon send the rounds downrange at a rate of ~2,000 rounds per minute, only when the last round has left the barrel does the barrel and action begin to recoil inside the stock along a central guide. When in sustained fire the rate of fire is closer to ~460 per minute.
The buffer spring below the barrel is compressed as the recoiling barrel and breech assembly moves. In sustained fire the buffer spring is partially compressed with each round, but in burst fire the buffer is compressed to its maximum hitting before the buffer housing (which is when recoil from the burst is felt by the operator), this is described as having the barrel and breech assembly ‘float’.
To ready the weapon to fire a magazine was loaded into the magazine channel on top of the G11, a magazine dust door, which automatically closed when unloaded, was depressed as the magazine was pushed home. The cocking handle on the left side of the butt was then actuated. The operator rotated the handle 360-degrees counter-clockwise until the weapon was cocked (essentially like winding a clock). The same process will eject any rounds left in the chamber once the magazine has been removed.
Gas tapped from the barrel cycles the cylinder drive system with gas pushing a piston back to act on a series of gears which rotated the rotary breech from horizontal to vertical to allow a new cartridge to drop into the breech. There was a vent for high pressure gas underneath the butt stock this prevented pressure build up and mitigated some of the thermal build up.
The G11 K1 was tested by the German Army in the late 1980s with adoption planned for the early 1990s. Heckler & Koch continued to develop the G11, entering the G11 K2 into the US Army’s Advanced Combat Rifle (ACR) trials alongside entries from Steyr, AAI and Colt [all of which we will examine in upcoming videos]. However, the fall of the Berlin Wall in 1989 and the collapse of the Soviet Union in 1991 meant that West Germany no longer had the huge amount of funds needed to field the G11. At the same time the ACR program ended inconclusively and the G11 project was finally abandoned.
The extreme complexity of the design, the inadequacy of the weapon’s ergonomics and its inevitably high production cost casts doubt on whether the G11 would ever have seriously been considered for widespread adoption. Regardless of this the G11 is a fascinating footnote in small arms history representing a false start along a technological avenue which, with the Lightweight Small Arms Technologies (LSAT) program, may still prove fruitful. Heckler & Koch and Dynamit-Nobel’s ambitious design marks one of very few serious and potentially successful attempts engineers to overcome the plateau that firearms technology is currently stuck on.
At the end of the Second World War the British Army had two primary infantry machine guns: the Bren light machine gun and the Vickers medium machine gun. These weapons had proved their worth, the Bren was especially well liked and the venerable Vickers continued to be a reliable workhorse.
In the late 1940s, the British Army recognised the Soviet threat to Western Europe. In 1947, Field Marshal Bernard Montgomery, the newly appointed Chief of the Imperial General Staff wrote a paper outlining rearmament plans based on intelligence estimates of how quickly the Soviet Union was likely to be ready for another full-scale war. Montgomery believed that Britain had just 10 years to develop new weapons and begin rearmament before the Soviet Union had recovered enough to launch an invasion of Western Europe. As such the British Army felt that rearmament needed to be complete by the late 1950s.
A number of large budget programmes were launched while small arms projects were also undertaken. These included the Infantry Personal Weapon programme which sought to develop a new intermediate calibre infantry rifle – the IPW programme later yielded Stefan Janson’s EM-2, a bullpup chambered in .280, which was briefly adopted as the Rifle No.9. The FN FAL was later adopted due to changes in political circumstances – a long, fascinating story for another article. The companion to the IPW programme was the development of a Sustained Fire Machine Gun also chambered in .280. The TADEN, a belt-fed derivative of the Bren firing the new .280 round was designed by Harold Turpin (‘T’), the Armament Design Establishment (‘AD’) and Enfield (‘EN’). With the abandonment of the IPW the TADEN was also abandoned but its design greatly influenced the later X11.
Another major small arms programme was the search for a new machine carbine (or submachine gun). This saw the testing of designs from Sterling, BSA and Madsen – with the Sterling finally adopted as the L2.
The other major small arms project was the programme to find a new section level machine gun. The German MG34 and MG42 had impressed the Allies during the war, so much so the US went as far as to clone it with the T24. After the abandonment of the EM-2 and TADEN machine gun the British issued a new specification for a lightweight sustained fire machine gun, chambered in the 7.62x51mm round recently adopted by NATO, in the mid-1950s.
The design team at the Royal Small Arms Factory at Enfield developed a belt-fed derivative of the Bren light machine gun. The X11 series of prototypes sought to convert the Bren’s proven design into a weapon capable of sustained fire. The X11 made a number of changes to the Bren included the addition of a detachable butt/grip/trigger assembly which could be swapped for a pair of spade grips and a paddle trigger for static sustained fire from a tripod. This resulted in the pistol grip being located much further back than the traditional Bren’s.
It appears that during the mid-1950s British military parlance described the General Purpose Machine Gun as a Sustained Fire Machine Gun (SFMG). From the available photographs it appears that the L4 and X11 use the same barrel with its distinct flash hider. The receivers of all the prototypes appear to be milled to attach the optical long range sight seen above.
The main drawback with the X11 was its feed mechanism. The feed slide was indexed by a rotating vertical feed shaft which was driven by the gas piston’s recoil. This created a considerable amount of friction within the action. It had the effect of causing failures to feed during adverse conditions testing and elevated firing tests. A series of four X11 prototypes were developed with Harold Turpin (co-designer of the STEN gun and later TADEN) working on the new gun. Each prototype appears to have a sightly different trigger configuration. The most interesting of these is a two-finger double-crescent trigger reminiscent of the MG-34’s – from the photographs it appears that the conventional selector lever, used in the X11E2, was replaced with a fire-selector system similar to the MG-34’s (upper crescent – semi-auto, lower crescent – full-auto). However, the trigger of the example of the X11E4 examined by Vic (serial number #11) was fully automatic only, despite its crescent shape.
Below are photographs of examples of the three types held at the Royal Armouries:
The X11 was tested against the M60, French AA-52, Swiss MG51, Danish Madsen-Saetter, German MG-3, and the Belgian FN MAG. The FN MAG, designated the X15E1 by the British, fared best in the trials with the X11 coming second due to its feeding issues. In January 1958, the British abandoned the X11 and moved to adopt the X15E1 general purpose machine gun, negotiating a license for its manufacture. The weapon was finally adopted as the L7A1 in 1961, with production at Enfield beginning in 1963. It seems that the Birmingham Small Arms Company were a latecomer to the competition having developed the another belt-fed Bren gun derivative known as the X16.
The Bren did continue in service after the switch to 7.62x51mm. In 1954, before beginning work on the X11, Enfield had developed the X10E1. Taking a Canadian manufactured 7.92x57mm Bren breech block and converting it to cycle the new round. The X10E1 was formally adopted as the L4. The L4 remained in service, alongside the L7, into the early 1990s. The L7 GPMG continues to be used by the British Army.