Live Fire: L2A3 Sterling SMG

In this episode we bring you our first live fire and slow motion footage! Matt had the opportunity to fire a British L2A3 Sterling submachine gun and Vic captured some great video. The Sterling was adopted by the British military in 1954 and standardised as the L2A3 in 1956.

Designed by George Patchett, at the Sterling Armaments Company, development began towards the end of the Second World War. After a decade of development and testing the British Army adopted the Sterling. It remained in service into the 1990s and Sterling produced and sold the gun overseas until the company closed in the late 1980s. Licensed versions of the Sterling were made in Canada and production continues today in India.

While the Sterling Armaments Company, the original developers and manufacturer of the gun, produced L2A3s for the government and the commercial market most of the British Army’s Sterlings were made by the government owned Royal Ordnance Factory in Fazakerly near Liverpool.
The gun featured in the video is a Fazakerly-made British Army L2A3, the magazine is also of the slightly simplified government pattern.

slow motion Sterling smg
Frame from the slow motion footage showing a spent 9x19mm case being ejected from the L2A3 (TAB)

In this episode we look at the firing cycle of the L2A3 and how the weapon works. The Sterling uses a standard blowback action and this footage shows it firing in semi-automatic. We can see the breech block travel forward, strip a round from the magazine and chamber it. The round is fired and the breech block then travels rearward again before repeating the cycle.

In future videos we will discuss in-depth the design, development and history of the Sterling.

We would like to thank Graham over at www.slomocamco.com for the loan of the brilliant slow motion camera which captured this great footage!

British Trials Browning Automatic Rifle

During World War One the British Army had been early adopters of the light machine gun concept, recognising the mobility and firepower offered by the Lewis Gun as early as 1915. Despite the Lewis Gun’s proven track record after the war a lighter weapon was sought.

In the final months of World War One the US had begun fielding the Browning Automatic Rifle, Model of 1918, in what they had envisaged as a ‘walking fire’ role. Relatively soon after the war British Ordnance began the search for what they termed a ‘light gun’. They took an interest in the BAR ordering 25 Colt Model 1919 commercial guns for testing and evaluation at a cost of £1,575 in November 1920. According to James Ballou’s book on the BAR, Rock & a Hard Place, the serial numbers of these guns ran between C-100374 to C-100398. The Colt Model of 1919 differed little from the earlier US military model, the principle changes were the lack of a flash hider and the use of relocating of the recoil spring to the butt, acted on by a transfer rod, from inside the gas cylinder tube.

This batch of guns was adapted to chamber the rimmed British .303 round, necessitating a curved magazine, a .303 barrel, an adapted bolt, extractor and ejector. In April 1921 the BAR along with four other light machine guns (the Madsen, Beardmore-Farquhar, a Lewis Gun and strip and magazine fed Hotchkiss guns) at the School of Musketry at Hythe.

Colt Model 1925
Colt Model 1925 Browning Automatic Rifle (Royal Armouries)

The Browning fared well in the testing with the evaluating officer stating that for a “light gas-operated weapon the Browning has done remarkably well…” In fact the Browning was selected as first preference out of the five weapons tested. The testing board felt it was suitably light and would be the cheapest to manufacture. The board made a series of suggestions to improve the BAR for British service:

  1. Move the cocking handle to the right side of the weapon
  2. Fit a light bipod which is height adjustable 
  3. Ejection port and magazine well dust covers
  4. Gas regulator hole to be clear of threads of regulator
  5. Improved method of fixing position of gas regulator
  6. Stronger  butt
  7. Magazine well capable of receiving Lee-Enfield rifle magazines

No further action was taken until 1927 when it was decided that the Superintendent of Design should adapt several Brownings to improve the weapon for British service.  According to Jame Ballou’s book these new modified BARs were not all from the original batch of test guns, at least one was a Colt gun purchased through FN.

The adapted BARs had carrying handles, flash hiders, bipods, Lewis Gun-style pistol grips, new rear sight and protected front post, an ejection port dust cover and a redesigned butt stock. A number of other changes were also made including switching the charging handle to the right (this change was found to be less necessary with the addition of a pistol grip).

26262
Specially adapted British 1925 Trials BAR (Royal Armouries)

While the modified BAR’s came fairly close to being adopted the principle problem remained the weapon’s limited 20 round magazine. Various larger magazines such as a 40-round box magazine from Colt and a 30-round drum were considered. By 1930 several new light machine guns had appeared and the Browning was beginning to look obsolescent. The Czech vz. 26 would eventually be adopted as the Bren.

We recently had the opportunity to examine what we believe to be a British trials BAR. Vic examined the gun finding that rather than a commercial Model of 1919, purchased for the first set of evaluations, it was marked as a Model of 1925. Interestingly, however, rather than resembling a Colt M1925 it had all the characteristics of an earlier M1919.

TAB 303 BAR (2).Movie_Snapshot
A still from Vic’s video showing the disassembled .303 Model 1925 (TAB)

The gun examined, serial number C-102723, falls outside of the serial range James Ballou states belonged to the 25 original .303 BARs. While it is marked M1925 the gun shares none of the characteristics of an M1925 – lacking the reshaped wooden foregrip, stubby pistol grip and rate of fire reducer. It does, however, have the 1919’s style of stock, foregrip and its relocated recoil spring. Additionally, the gun has had a folding carry handle, very similar to that of the later British trials BARs, added.

With little solid information available there could be a number of reasons for this. Perhaps the BAR Vic was able to examine was purchased for the later trials (between 1925-30) and it underwent minimal alterations – there is some variation between the documented surviving examples. The discrepancy between parts and the model name is curious. It is possibly a mix of parts were used to assemble the weapon during experimentation with configurations and an M1925 receiver was used as the basis of the gun but it was assembled with an M1919 barrel and furniture.


Specifications:

Length: ~115cm / 45 in
Weight: .303 M1919 approximately 7kg, later trials guns between approximately 7.5-8.5kg
Sights: M1917 Rifle sights
Action: Gas-operated, rising bolt lock
Calibre: .303
Feed: 20-round curved box magazine


Bibliography:

The Browning Automatic Rifle, R.R. Hodges, (2012)

Rock and a Hard Place: The Browning Automatic Rifle, J.L. Ballou, (2000)

Video from the Institute of Military Technology showing a .303 M1919 BAR (source)

Colt Advanced Combat Rifle

This is the final of three introductory videos looking at the US Army’s ACR prototypes. We will be revisiting these rifles later to show disassembly and how they worked. You can check out our introduction to the H&K G11 here, our look at the AAI ACR here, the Steyr ACR here and  you can also find our in-depth ACR Program overview article here.

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.

DSC_0141
Colt ACR rifle submission Left and right side views of the Colt ACR (Matthew Moss)

It incorporated a variety of improvements including a new oil/spring hydraulic buffer to mitigate recoil. This resulted in a major decrease in the weapon’s recoil, Colt suggested as much as a 40% mitigation. A reshaped pistol grip and a hand guard which mounted a sighting rib for snap shooting – this stemmed from recommendations from the Human Engineering Lab. The weapon had a flat-top upper receiver which incorporated a weaver rail so a 3.5x optic (an early ECLAN) or a more conventional sight/carrying handle could be fitted.

DSC_0139
(Matthew Moss)

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 (MBC) designed by Knight’s Armament was also added. The Knight’s MBC reduced the rifle’s report by 13.5-decibels and also played an important role in recoil mitigation.

DSC_0138
Close up of the Knight’s Armament designed muzzle device (Matthew Moss)
DSC_0137
Right-side close up of the rifle’s receiver and rail mounted Eclan sight (Matthew Moss)

Colt’s duplex rounds were developed by the Olin Corporation and placed two projectiles nose to tail. The projectiles were copper jacketed steel penetrators. In theory the lead projectile would strike at point of aim while the second would strike somewhere near point of aim with in a theoretically limited area of dispersion. The forward round was 35gr while the second was slightly lighter at 33gr.

Colt's 5.56mm Duplex round (US Army)
Colt’s 5.56mm Duplex round (US Army)

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.

Another negative to the Colt entry was that, in addition to having to carry two types of 5.56mm ammunition,  its duplex round offered no improvement in weight and was infact slightly heavier than standard M855 ammunition. While the hydraulic buffer, muzzle device and furniture were not used later, some of the features developed for the ACR entry were later employed in the M16A3 and later A4. These included the selector configuration and the flat-top upper receiver.

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

You can find out overview article on the ACR program and all of the rifles here


Bibliography:

Advanced Combat Rifle, Program Summary, Vol.1, ARDEC, 1992 (source)

‘Revisiting the SPIW Pt.3’, Small Arms Review, R. Blake Stevens, (source)

The Black Rifle II, C. Bartocci, (2004)

Our thanks to the collection that holds these wonderful examples of the ACR rifles


Please do not reproduce photographs taken by Matthew Moss without permission or credit. ©The Armourer’s Bench 2018

Steyr Advanced Combat Rifle

This is the second of three introductory videos looking at the US Army’s ACR prototypes. We will be revisiting these rifles later to show disassembly and how they worked. You can check out our introduction to the H&K G11 here, our look at the AAI ACR here and  you can also find our in-depth ACR Program overview article here.

By the mid-1980s Steyr-Mannlicher were already leaders in unconventional small arms designs. In 1977 the Steyr AUG was adopted by the Austrian Army becoming the first generally adopted bullpup service rifle.  As such Steyr-Mannlicher’s entry was inevitably a bullpup. Designed by Ulrich Zedrosser the rifle used a gas piston driven rising chamber mechanism which rose and fell to chamber rounds.

DSC_0118
DSC_0115 Left and right side views of the Steyr ACR, note the small AUG-style (Matthew Moss)

The rifle’s action is described in a 1988 patent (US #4949493) granted to Zedrosser, it explains that ” chamber member, which is separate from the barrel… is reciprocable between a firing position and a loading position in a direction which is transverse to the longitudinal direction of the barrel.” This means that the chamber rises and falls, with the rifle firing from an ‘open bolt’.

The patent goes on to explain the weapon’s action:

When the chamber member is in its loading position its chamber is freely accessible and at one end communicates through a loading opening of the firing block with the interior of a magazine holder and at the other end communicates through an ejection opening of the firing block with an ejection shaft. For the performance of the loading and unloading operation, a slider is provided, which is movable in the longitudinal direction of the barrel and carries a feeder, which is movable from a first end position… when the chamber member is in its loading position, and the movement of the chamber member from its loading position to its firing position is adapted to be initiated before the feeder reaches that end position in which the feeder extends into the loading opening.
Steyr_ACR_layout_schematic
Patent drawing showing the Steyr ACR’s bullpup layout (US Patent Office)

One of the other patents (US #4817496) protecting the design explains the weapon’s gas system:

In order to provide a gas drive which is particularly simple and functionally reliable, light in weight and compact, the barrel is provided with a collar or the like, which constitutes a stationary pneumatic piston, and the pneumatic cylinder consists of a sliding sleeve, which surrounds the collar and is longitudinally displaceable between stops.

US4949493-1
Patent diagram showing the Steyr ACR’s action (US Patent Office)

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, magazine release, 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 and the stock extends further forward to encompass the barrel and gas system. The rifle could be fitted with a variable 1.5x to 3.5x optic or use iron sights.

DSC_0150
Comparison of the Steyr ACR with the earlier AUG (Matthew Moss)

As discussed earlier the rifle does not use a conventional bolt, instead it uses 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.

Steyr's Polymer Cased Flechette round (US Army)
Steyr’s Polymer Cased Flechette round (US Army)

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.

ACR Program Summary recognised the Steyr ACR entry as “the simplest weapon, the simplest round, and the most cost effective approach of any of the ACR contenders.” The report noted that the weapon’s “greatest current deficiency is its poor round to round dispersion characteristics.” This was a criticism levelled at both the flechette firing entries, it essentially ended the US Army’s interest in flechette firing individual weapons, relegating the concept to larger area effect weapon systems.

Specifications (From ACR Program Summary):

Length: 30 inches / 76cm
Weight: 8.5 lbs / 3.86kg
Sights: Iron or variable 1-3.5x optic
Action: gas-operated, rising chamber
Calibre: 5.56mm plastic cased flechette
Feed: 24-round magazine

You can find out overview article on the ACR program and all of the rifles here


Bibliography:

Advanced Combat Rifle, Program Summary, Vol.1, ARDEC, 1992 (source)

‘Revisiting the SPIW Pt. 1-3’, Small Arms Review, R. Blake Stevens, (123)

Steyr’s ACR entry was extensively protected by various patents:

US #4944109
US #4817496
US #4930241
US #4949493
US #4916844
US #4760663
US #4739570
US #4941394

Our thanks to the collection that holds these wonderful examples of the ACR rifles


Please do not reproduce photographs taken by Matthew Moss without permission or credit. ©The Armourer’s Bench 2018

AAI Advanced Combat Rifle

This is the first of three introductory videos looking at the US Army’s ACR prototypes. We will be revisiting these later to show disassembly and how they worked. You can check out our introduction to the H&K G11 here. You can also find our in-depth ACR Program overview article here.

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.

4 guns from AAI's family of weapons 60s SPIWs
AAI SPIW family of weapons from the early 1960s (Reproduced in Stevens & Ezell’s SPIW Deadliest Weapon)

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.

AAI's Caseless Ammunition Rifle (US Army)
AAI’s Caseless Ammunition Rifle, another image available here (US Army)

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.

Left of the AAI ACR rifle (Matthew Moss)
Left-side view of AAI Corporation’s ACR entry (Matthew Moss)
AAI Corp ACR rifle (Matthew Moss)
Right-side view of AAI’s ACR entry (Matthew Moss)

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.

DSC_0146
An AAI Corporation ACR marked serial number 20 (Matthew Moss)

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.

Front end of AAI ACR (Matthew Moss)
The fore-end of the AAI ACR, note the front sight post and muzzle device which reduced muzzle climb during burst firing (Matthew Moss)

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.

AAI ACR Ejection Port (Matthew Moss)
Close up of the right-side of the AAI ACR, note the ejection port and moulded plastic case deflector, selector level, paddle magazine release and sight mount (Matthew Moss)

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.


Bibliography:

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


Please do not reproduce photographs taken by Matthew Moss without permission or credit. ©The Armourer’s Bench 2018.

Advanced Combat Rifle Prototypes

4 ACR program Rifle (Matthew Moss)
The four rifles tested during the final phases of the ACR program, AAI, Colt, H&K, Steyr (Matthew Moss)

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.

US Army Future Sldier 1959
US Army’s 1959 Future Soldier Concept, with M14 (LIFE)

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

AAI Corp ACR rifle
AAI Corporation’s ACR entry (Matthew Moss)

Check out Vic’s video on the AAI ACR and an article with further detail here

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.

Diagram showing AAI's saboted flechette round inside a 5.56x45mm M855 case (US Army)
Diagram showing AAI’s saboted flechette round inside a 5.56x45mm M855 case (US Army)

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

Colt ACR rifle submission
Colt’s ACR entry (Matthew Moss)

Check out Vic’s video on the Colt ACR and an article with further detail here

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.

Colt's 5.56mm Duplex round (US Army)
Colt’s 5.56mm Duplex round (US Army)

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

Heckler & Koch's G11K2, ACR entry
Heckler & Koch’s G11K2, ACR submission (Matthew Moss)

Check out our full article on the G11 and our introductory video showing two examples of the weapon partially disassembled here

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.

g11round5
Diagram showing the composition of the G11’s telescoped caseless ammunition (source)

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.

Specifications (From ACR Program Summary):

Length: 29.5 inches / 74.9cm
Weight: 9.15 lbs / 4.15kg
Sights: Variable 1-3.5x optic
Action: gas-operated, rotary breech
Calibre: 4.92mm caseless
Feed: 45-round single stack magazine

Steyr-Mannlicher

Steyr ACR Rifle
Steyr ACR entry (Matthew Moss)

Check out Vic’s video on the Steyr ACR and an article with further detail here

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.

Steyr's Polymer Cased Flechette round (US Army)
Steyr’s Polymer Cased Flechette round (US Army)

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.

Specifications (From ACR Program Summary):

Length: 30 inches / 76cm
Weight: 8.5 lbs / 3.86kg
Sights: Iron or variable 1-3.5x optic
Action: gas-operated, rising chamber
Calibre: 5.56mm plastic cased flechette
Feed: 24-round magazine


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.”

This last observation is something that is again now being developed in the Lightweight Small Arms Technologies (LSAT) program, which has now been linked with the US Army’s current Next Generation Squad Weapon program.

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.


Bibliography:

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 rifles


Please do not reproduce photographs taken by Matthew Moss without permission or credit. ©The Armourer’s Bench 2018

15-Inch Vickers Battery at Fortalesa Isabel II

Last summer I was lucky enough to visit the vast Fortalesa Isabel II which defended the port of Mahon, in Menorca. One of the fort’s most impressive sights is its huge 15 inch gun battery.

The Spanish island of Menorca, in the Balearic Islands, has a long and storied military history. The strategically important harbour of Mahon was historically the envy of the British, Spanish and French and was the reason for Fortalesa Isabel II’s construction. The for was the last major fortification built on the island, with the Spanish military beginning construction in 1850. A second phase of major improvements was made during 1853-1864. Work to improve and modernise the fort continued into the 20th century.

Fortalesa Isabel II main gate (Matthew Moss)
The ornate main gate of the fort, defended by a counterguard and rifle slits either side of the gate (Matthew Moss)

The Fortress is built on a beautiful rocky headland of La Mola at the mouth of the harbour and covers about a square kilometre. Construction was a massive undertaking and took over twenty years to complete, costing over nine million pesetas. The fortifications are some of the Mediterranean’s most impressive of the period.

The fort is a maze of tunnels, galleries, casements and buildings surrounded by a deep, dry moat. The fort’s first line of defence consisted of a moat 9 metres (30 feet) deep covered by rifle loop holes for infantrymen and embrasures for artillery. Interlocking fields of fire defend the landward approach to the fort’s main entrance, the Queen’s Gate.

Map of the La Mola peninsular and fort
Map showing the layout of the fort during the 19th century before the 15 inch guns were added (source)

Designed to dominate the entrance to the harbour the fortress was intended to hold 160 artillery pieces of various sizes, including Krupp guns and howitzers, many of these protected by strong stone casements. The fort’s armaments evolved overtime from muzzle-loaders to faster firing breech-loaders.

The Spanish continued to upgrade the fort’s guns over the decades mounting rifled guns and howitzers of various calibres ranging from 15cm to 30.5cm. In addition to the fort’s guns the defences also included mines in the harbour mouth and later a battery of shore launched torpedoes.

By the early 20th century the fort’s guns were increasingly obsolete against the backdrop of the naval revolution that saw Dreadnoughts come to dominate maritime warfare. With advances in naval architecture, armour and guns the Spanish government decided to purchase a number of massive 15 inch naval guns that could fire a 1,895 lb (860kg) shell up to 22 miles.

One of La Mola's 15 inch guns in position
One of the fort’s two 15 inch Vickers guns in position on Cape Espero (Matthew Moss)

Spain purchased 18 of these massive guns made by the British Vickers company, they had originally been designed for the cancelled Brazilian battleship Riachuelo. In Spanish service the guns were officially designated the Costa de 38.1cm Modelo 1926. During the 1930s the new coastal guns were installed on both the Spanish mainland and Menorca. Two guns placed in the Castillitos Battery, defending Cartagena, opened fire on a Spanish Nationalist fleet, during the dying days of the Spanish Civil War. While Menorca’s guns never fired a shot in anger, they acted as a deterrent.

The first guns reached Mahon in 1932, with a second arriving in 1936, these were mounted on the cliffs of Cape Espero on the La Mola peninsular. The guns were so huge they had to be transported to the fort on a specially built railway pulled by hand and traction engine. These formidable new guns brought Fortalesa Isabel II’s armament up to date, enabling it to protect Mahon from any modern warship.

15 inch gun being dragged by a traction engine through mahon
One of the massive 15 inch guns being pulled along its special track by a traction engine through the streets of Mahon (source)

The 15 inch (or 381mm) Vickers battery at the fort was positioned 70m above sea level and commanded the entrance to the harbour. Six guns were eventually sent to Menorca with two  placed on La Mola, two more installed in a battery at Favaritx (the remains of which can be seen here) in the north of the island and a pair at a battery near Llucalari in the south of the island.

While the guns at Favaritx were later removed, the guns at Llucalari remain. The fact that six of these massive and expensive naval guns were placed on Menorca shows its strategic value during the period.

Satellite photo of the 15 inch battery at Llucalari
Satellite photo showing Menorca’s other 15 inch battery at Llucalari (google maps)

The guns were mounted in barbettes which allowed the guns to traverse up to 300 degrees. The gun housing of the turret was armoured but while it would not protect the crew from a direct hit, it would protect against shrapnel. Below the guns were magazine stores for both cordite charge bags and projectiles, the machinery needed to rotate and move the gun and the motors to power it. Inside the turret were controls to open and close the breech, lift and lower the loading tray and aim the gun. The guns had a potential maximum range of 35km or 22 miles, however, the guns at La Mola lacked the necessary range-finding equipment to achieve this range.

Inside the 15 inch gun turret
A contemporary photograph showing the interior of the gun turret. A shell is sat on the loading try ready to be pushed into the breech. (source)

The ancillary buildings for the battery on La Mola are built just behind the two gun emplacements with offices, stores and barracks built in an old quarry. As well as the two main guns the battery was supported by four faster firing 6 inch Vickers guns.

15 inch Vickers gun firing in the 1980s
One of Menorca’s 15 inch guns firing c.1980s (source)

With the eruption of the Spanish Civil War in 1936, Menorca was initially held by the Republicans. But in 1939, the island fell to General Franco’s Nationalists and the fort’s military prison was used to house a number of prominent Republican prisoners. Throughout the Cold War the fort continued to be used by the Spanish Army as a training centre but the rise of air power, the invention of the cruise missile and nuclear weapons rendered the fort and its guns increasingly obsolete.

The last of Spain’s 15 inch guns were finally decommissioned in the mid-2000s, after nearly 80 years in service. Fortalesa Isabel II and her two massive guns never saw action, and today the site is maintained as an impressive museum which is well worth a visit.


Specifications:

Length: 18m or 59 feet
Weight: 86.9 tons
Action: breech-loading
Calibre: 15 inch or 381mm
Elevation -5 / +40 degrees
Traverse: 300 degrees
Rate of fire: 2 rounds per minute


Bibliography:

The Fortress of Isabel II on La Mola in Mahon Harbour (19th 7 20th Century), F. Fornals (2007)

The Conquests and Reconquests of Menorca, M. Mata (1984)

Guns of Cartagena, espele.net, (source)

‘Yo hice la Mili en La Mola de Menorca’, Facebook group with excellent contemporary photos (source)

www.fortalesalamola.com


Please do not reproduce photographs taken by Matthew Moss without permission or credit. ©The Armourer’s Bench 2018.