Sometimes all is not as it seems. That was the case when we examined this Steyr AUG. From the barrel and bipod it appeared to be an AUG in an HBAR or Heavy Barrel configuration but on closer inspection we found that it was in fact a rifle receiver, bolt and bolt assembly and chassis that had been paired with an HBAR barrel assembly.
Vic with the Steyr ‘HBAR’ (Vic Tuff)
Ordinarily, the HBAR could be modified to fire from an open, rather than closed, bolt. This example has the standard AUG progressive trigger for semi and full-auto. It does not have the modified bolt carrier, striker or trigger mechanism.
The HBAR has a 4x optic, rather than the rifle’s 1x, while the HBAR-T can be fitted with an optic like a Kahles ZF69 6×42.
A dedicated ‘LMG’ marked AUG stock and bolt carrier (Vic Tuff)
Adoption of the AUG HBAR does not appear to have been widespread and Steyr don’t currently list it as an option amongst their upgraded AUGs. For more Steyr we have previously examined a Steyr AUG SMG conversion and a Steyr MPi 81. We’ll take an in depth look at the AUG and AUG HBAR in the future.
Overall Length: 35.5in (90cm)
Barrel Length: 24.4in (62cm)
Weight: 8.6lb (3.9kg)
Action: Gas operated, rotating bolt – the HBAR typically fires from an open bolt, but this rifle-based example fires from a closed bolt.
Capacity: 30 or 42-round box magazines
Calibre: 5.56×45mm
Developed in the late 1960s and introduced in 1969/70 the MPi 69 was Steyr’s entry into an already crowded European submachine gun market. Heavily influenced by the Israeli Uzi it had a bolt which telescoped over the barrel and fed from a box magazine that was inserted through a magazine well-come-pistol grip.
The MPi 69 weighed 6.5lbs (2.93kg) unloaded and had a polymer lower receiver into which a stamped metal upper inserted. Unlike the Uzi it had a collapsing, rather than folding stock, similar to the M3 submachine gun’s, and was cocked not by a handle but by pulling the sling (which was acted on the bolt) to the rear.
Steyr MPi 69 (Rock Island Auction Company)
The MPi 69 remained in production into the early 1980s when it was replaced by the improved MPi 81. Moving away from the slick-cocking ‘gimmick’ the MPi 81 had a conventional, non-reciprocating, charging handle on the left side of the receiver. The MPi’s polymer lower allows it to be a pound lighter despite being slightly longer as a result it also balances better than the standard Uzi carbine.
Steyr MPi 69 diagram (Steyr Manual)
The MPi submachine guns fed from 25 or 32 round box magazines and both guns had a heel-type magazine release paddle in the base of the pistol grip. They also shared their magazines with the AUG 9x19mm submachine gun conversion. Check out our earlier video on the Steyr AUG conversion here.
Steyr MPi 81 (Rock Island Auction Company)
The MPi submachine guns fire from an open bolt and had a 10in barrel and has a push through safety with settings for safe, semi and full auto and unlike the Uzi it does not have a grip safety – simplifying manufacture.
The MPi also has a progressive trigger which when set to full-auto will allow the user to fire semi when pulled to the first stage and full when pulled fully to the rear. While the MPi 69 had a cyclic rate of around 500 per minute, the MPi 81 increased this rate to ~750rpm.
Steyr MPi 69 disassembly diagram (Steyr Manual)
The MPi can be field stripped by simply rotating the receiver end cap up 90-degrees and pulling the bolt out the rear. The gun can be further stripped but the moulded polymer lower receiver can be difficult to remove from the upper. Like the Uzi the barrel nut is unscrewed to remove the barrel.
The MPi 81 fully disassembled (Vic Tuff)
It is unclear just how many MPi submachine guns were produced but they didn’t see any significant contracts beyond a few small sales to police forces and militaries.
The MPi 81 remained in production into the early 1990s when it was replaced by the smaller and more compact Steyr TMP in 1992. In turn the TMP design was sold to B&T a decade later.
Our thanks to the collection that let us take a look at this MPi 81 and to our friend Miles Vining for sharing some of his shooting footage of the MPi 81 with us, check out his video here and more of his work at www.silahreport.com.
In the second video Matt tackles the Heckler & Koch G11 and gives an update on the colouring book and the channel:
Thanks for watching chaps & thanks so much for your support in 2019, we greatly appreciate it. It’s been a busy year and we hope that you’ve all enjoyed our videos!
You can still pick up a copy of the ACR colouring book and the G11 sticker at www.armourersbench.com/shop. we’re very much looking forward to seeing your artistic sides when you send us some photos of your colouring to – contact@armourersbench.com.
The Armourer’s Bench are proud to introduce our very first ‘informative colouring (coloring) book’. Not only can you colour in the prototypes from the US Army’s Advanced Combat Rifle trials but you can also learn about the guns, how they worked, performed and the outcome of the trial as you colour!
Why a colouring book? Well, simply put, no one else has done one before! With the help of our brilliant illustrator, Lauren McInnerney, we put the book together to give you guys something a bit different, something fun!
We have a limited run of these little books and we will do our very best to get them our ASAP if you order them for Christmas.
The book includes detailed original illustrations of each of the four ACR guns: the AAI, Colt, Steyr and of course the iconic HK G11. The 8-page booklets are 8×6″ (or A5 sized) and are available now from our website for $6.00, plus shipping.
All the funds raised from the sale of the books will go toward supporting TAB through 2020.
But wait! That’s not all! We also have some extremely cool new stickers available. These 4″ cutout vinyl stickers feature the TAB logo on an illustration of the G11.
And last but not least we also have a small run of TAB logo badges available too!
The Steyr AUG or Armee Universal Gewehr (Army Universal Rifle), is one of the earliest Bullpup military issued rifles (if not the earliest) adopted by a military, i.e. the Austrian Military as the Stg77 in 1977. Other early bullpups being the British L85 (SA80), and the French FAMAS. The AUG went on to be adopted by the Australian military and eventually licence built there as the Austeyr F88, the New Zealand Defense Forces, Irish Army, and various other military and police forces worldwide.
Belgian Federal Police officer with AUG 9x19mm SMG (source)
In 1990, Steyr developed the first variant of the AUG/9mm Carbine and a 9mm conversion for the AUG-A1 rifle. The conversion consists of a new bolt group, barrel and magazine-well insert. The AUG/9mm Carbine uses the standard 25 round or 32 round magazines from the Steyr MPi 69/81 submachine gun series which is also a Steyr product. Whilst the conversion of standard rifles with the conversion kit is perfectly viable there were difficulties with the standard ejection port due to fired cases rebounding back into the action and also striking the firer!
The 9mm conversion ‘kit’ was replaced with the second variant of the ‘dedicated’ AUG Carbine in 9mm with an improved magazine-well adapter and an ejection-port shield or barrier, this could also be retrofitted on existing 5.56mm housings as an improved conversion kit including an ejection-port shield. However, in 1995 a dedicated AUG /9mm Carbine was introduced with the ejection-port shield molded as an integral part of its stock/housing (the marketing of the 9mm conversion kit being discontinued).
Steyr AUG-SA 9x19mm Carbine Conversion (RIA)The latest iteration of the weapon the Steyr AUG A3 XS, note the lack of ejection port on the left side and the picatinny optics mounting rail (source)
The AUG/9mm Carbine the barrel does not have a flash suppressor, but has a threaded section behind the muzzle to allow the mounting of aftermarket suppressors etc. The barrel mounts exactly the same as the 5.56mm barrel but does not have a gas tappet system as the 9mm carbine functions as a closed-bolt, blowback. The bolt of the 9mm variant is integral with what is normally the bolt carrier in the standard AUG, the bolt face is machined directly in the bolt carrier face.
Belgian Federal Police officer with AUG SMG with ejection port case deflector (source)
Users of the 9mm variant are mostly police or security forces, notably the Kuwaiti Military Police fielded the 9mm SMG/carbine for some time until surplused a few years back. Ironically the 9mm SMG/carbine is fielded by the Belgian Federal Police whilst the Austrian Gendarmerie used to field the FN (Belgium) manufactured UZI!
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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.
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.
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.
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.
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)
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.
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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’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 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)
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 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)
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.
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.
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)
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.”
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.
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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
Left and right side views of the Steyr ACR, note the small AUG-style (Matthew Moss)
The Armourers Bench 