Heckler & Koch HK33

Heckler & Koch’s first 5.56×45 rifle, the HK33, was introduced in the late 1960s as a response to the emergence of the new 5.56x45mm round and the introduction of the FN CAL. The HK33 is little more than a scaled down version of HK’s successful 7.62×51 G3. Developed by Tilo Möller, the HK33 used the same roller delayed blowback action and shares most of the G3’s features.

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Left & right views of the HK33 (Matthew Moss)

It has a stamped receiver and uses the same plastic furniture and pistol grip/trigger mechanism housing as the G3. The rifle is 39 inches or 92cm long and is by no means a light weapon, weighing around 4kg or 8.7 lbs. The HK33 feeds from 25, 30 or 40 round proprietary HK magazines.

The rifle came in main two main variants a full length version with a fixed stock, which could be fitted with a collapsing stock, and a shortened K-variant with a shorter barrel. The weapon came with either a safe, semi and full auto or safe, semi, 3-round burst fire control mechanism.

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HK factory brochure showing the variants of the HK33 (Heckler & Koch)

The HK33 was not adopted by the West German Army, however, it did see extensive use with Germany’s federal state and police forces and the Bundeswehr special forces. While it wasn’t adopted at home it was a successful export weapon with dozens of countries purchasing and adopting the rifle. France tested the improved HK33F in the Army 1970s and although it performed well the FAMAS was adopted instead. A production license was sold to Thailand who adopted the HK33, purchasing 40,000 rifles and the license to manufacture 30,000 more. Thailand also developed their own unique bull pup version of the rifle, the Type 11.

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HK33 field stripped (Matthew Moss)

Malaysia also purchased 55,000 HK33s and the Spanish Guardia Civil used them for a time. The manufacturing rights for the HK33 were also sold to Portugal for production at Fabrica Militar de Prata and to Turkey where it remains in production at MKEK.

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A comparison of the HK33’s bolt with the later HK G41 (Matthew Moss)

HK produced the HK33 from 1968 through to the late 1980s. It also provided the basis for the HK53 5.56 ‘submachine gun’ which we have covered previously. It was also the basis of the less successful G41, which we’ve also covered in a full length episode, you can find this here. The similarities with the HK33 are easy to see but the G41 has a number of subtle changes.

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Specifications (from 1985 factory brochure):

Overall Length (with fixed stock): 36in /92cm
Barrel Length: 15.7in / 40cm
Weight: 8.7lbs / 4kg
Action: Roller-delayed blowback
Capacity: 25, 30 or 40-round box magazine
Calibre: 5.56x45mm


Bibliography:

Full Circle: A Treatise on Roller Locking, R. Blake Stevens (2006)

HK33 Factory Brochure, c.1966 (source)

HK33E Factory Brochure, c.1985 (source)

Heckler & Koch G41

In 1981, Heckler & Koch introduced what would be their last infantry rifle that used their tried and tested roller-delayed blowback action, the HK G41. In October 1980, following NATO’s smalls arms and ammunition testing during the late 1970s, a meeting of NATO Armament Directors, agreed to standardise to the 5.56x45mm round favoured by the United States since the mid-1960s. Standardisation Agreement (STANAG) 4172 saw NATO standardise on the Belgian/FN SS109 ball round. At the same time Draft STANAG 4179 proposed adopting US 30-round M16 magazines as the standard 5.56 magazine pattern, while this proposal wasn’t ratified the M16’s magazine became the de facto standard.

At this time Heckler & Koch were engaged in a major engineering project to develop the G11 caseless ammunition-firing individual weapon. Their main offering for the 5.56x45mm rifle market at the time was the HK33, a rechambered version of the 7.62x51mm G3 developed by Tilo Moller, which was introduced in 1965. The HK33, however, used a proprietary HK magazine and was not compatible with the M16’s magazines. In 1977, as the NATO trials began and it became clear that 5.56x45mm would be adopted, HK began to develop what would become the G41. In 1979 with initial development completed HK submitted 18 G41s for testing with the West German Army. It wasn’t until 1981 that HK introduced the G41 onto the market.

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Left and right profile views of the G41 (Matthew Moss)

While continuing to use the same roller delayed blowback operating system as the G3, HK33 and MP5, the G41 embodied a number of improvements. While still using a stamped metal receiver it utilised 1mm thick high tensile steel rather than the 1.2mm thick steel used by the HK33. This helped to lighten the receiver. The new rifle also used a lighter bolt assembly, paired with a new recoil spring which comprised of five wound strands around a central coil, rather than a single coil, which had a longer stroke. This acted to lower the felt recoil. The G41, however, had a higher rate of fire at around 850 rounds per minute compared to the 750 rounds per minute of the HK33.  Some of the G41’s bolt geometries were reworked and a new extractor was added.

The G41’s lower receiver was redesigned to allow the rifle to feed from STANAG magazines rather than HK’s earlier proprietary magazines. The cocking lever and forward assist were taken from the HK21A1 (XM262) general purpose machine gun, developed for the US SAW trials.

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HK G41 (top) and HK33 (bottom) field stripped (Matthew Moss)

It also had a new more triangular polymer foregrip and added a plastic dust cover to the ejection port, a NATO pattern optics mount (meeting STANAG 2324) replaced HK’s claw-mount system, and a spring-loaded folding carrying handle near the centre of balance was added. Importantly it also added a last round hold open device and a bolt release catch, on the left side of the lower receiver.

The usual thumb serrations on the side of the bolt, for pushing the bolt home, were replaced by a prominent forward assist, similar to that found on the M16A1 and other HK weapons such as the HK21 light machine gun and the PSG-1 sniper rifle. HK sales literature described it as a ‘low noise’ forward assist and the manual describes the “quiet cocking of the weapon” – essentially riding the cocking handle back into battery and then pushing the forward assist to lock the action, the system is not as ‘low noise’ as advertised.

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Right side of the G41, note the addition of a forward assist and dust cover (Matthew Moss)

Another important feature of the rifle was the inclusion of a three-round burst setting alongside semi and fully automatic. The G41 could mount a standard G3 bayonet, fit an M16 bipod and had a flash hider designed to enable it to fire NATO standard rifle grenades. The 40mm HK79 under barrel grenade launcher could also be mounted to all variants of the G41, simply swapping it out for the polymer forend. HK referred to this set up as the G41-TGS or ‘Tactical Group Support system’.

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Spread from a 1985 HK promotional product brochure showing the various G41 configurations (HK)

The G41 came in a number of variants with designations A1 to A3. The base rifle had a fixed buttstock and its rifling had 1 turn in 7 inches with a right-hand twist, in a 18.9 inch barrel. The A1 had a 1 in 12” twist barrel and fixed buttstock. The A2 had a collapsing, single position stock and 1 in 7” inch twist rifling, while the A3 had 1 in 12” inch twist rifling. The 1 in 7” rifling was optimised for the new SS109, while the 1 in 12” optimised for the US M193 round. There was also a shortened G41K model which had a collapsing stock and a 15 inch barrel available with both rifling types.

One of the main issues with the G41 was its weight. Despite efforts to lighten the sheet metal receiver, it weighed more than its predecessor the HK33. According to measurement data compiled by researcher Nathaniel F, unloaded the G41 weighs in at 4.31kgs or 9.5 lbs, this is a full pound heavier than the HK33. A contemporary M16A2 weighed 3.39kg or 7.5 lbs while the Spanish CETME L, a similar stamped receiver rifle chambered in 5.56×45, weighed 3.72kg or 8.2 lbs. The rifle eventually adopted by the Bundeswehr, the HK G36, weighed 3.13kg or 7.3 lbs.  The G41K with its collapsing steel stock wasn’t much lighter, weighing 4.3kg or 9.5 lbs, according to HK sales literature. Another potential issue may have been reliability with the move to the STANAG magazine rather than the optimised proprietary HK magazines may have introduced some issues.

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The bolts of the HK G41 (top) and HK33 (bottom), note the redesigned extractor, forward assist serrations on the bolt carrier and the G41’s thicker but shorter recoil spring (Matthew Moss)

Following NATO’s decision the early 1980s saw a large number of countries looking to replace their ageing 7.62x51mm battle rifles. Sweden began to look for a 5.56x45mm rifle to replace its licensed version of the G3, the Ak4, in the late 1970s. HK could initially only offer the HK33 but the G41, tested later, was also rejected by the Swedes in favour of FN’s FNC. Italy sought to replace the BM59 with a more modern rifle and HK entered into an agreement with Luigi Franchi which saw them offer both the original HK configuration and the develop their own, slightly modified version, the Franchi mod. 641, but the Beretta AR70/90 was selected. Similarly, in 1984 Spain decided to adopt the indigenously developed CETME L. In 1986 the HK G41 was also submitted to the Irish Army’s trials to replace the FN FAL, it was beaten by the Steyr AUG. Initially West Germany had hoped to procure up to 20,000 HK G11 rifles per year, with a total of 224,000 in service by 2003.

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HK’s G11 and G41 (Matthew Moss)

The collapse of the Soviet Union and the subsequent reunification of Germany saw Federal budgets stretched and the G11 programme was subsequently abandoned entirely. The Bundeswehr still needed a suitable rifle to replace the G3 and in the 1990s sought a lighter weight rifle. HK felt their HK50 project, in development since the mid-1970s was a better bet than the heavier G41, and following Bundeswehr trials the G36 was subsequently adopted in 1997. Sadly, I have not been able to get a hold of any of the trials reports from the nations that tested the G41, so can not say with certainty why the countries mentioned above rejected HK’s rifle.

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Graphic from HK’s manual for the G41 (HK)

From photographs of members of the Turkish Gendarmerie special operations group training at the Foça Commando School, dating from the early 2010s, it appears that Turkey either purchased a number of G41s or Turkey’s state-owned defence manufacturer, MKEK, produced an unknown number under license.At some point in the 1980s the British Army also tested a small number G41s with serial numbers #11131, #11832 and #11833 remaining in UK collections.

Denmark’s elite Jaegerkorpset and Froemandskorpset used the G41 for a time and Argentina’s special forces, including the Grupo de Operaciones Especiales, have also been photographed with both HK G41s and G41A2(collapsing stock) fitted with the TGS package comprising of the HK79 under barrel grenade launcher.

Argentine commandos with HK G41
Argentina’s Grupo de Operaciones Especiales on parade with G41s and the G41-TGS, grenade launcher package (source)

The G41 represents the last evolution of HK’s infantry rifles using the roller delayed blowback action. It comes from a period when HK were developing what they hoped would be the next generation of small arms technology and with the collapse of the G11 programme and the lack of interest in the G41 the company faced financial uncertainty throughout the early 1990s. HK’s move away from the roller delayed blowback action to a more conventional gas operated rotating bolt system, combined with lightweight polymers, in the G36 proved to be more successful than the ill-fated G41.

If you enjoyed the video and this article please consider supporting our work here.


Specifications (standard G41 rifle model):

Length: 39in (99cm)
Weight (unloaded): 4.31kgs or 9.5 lbs
Barrel Length (not including flash hider): 17.7in (45cm)
Action: Roller-delayed blowback
Calibre: 5.56x45mm
Feed: 30 round STANAG magazines
Cyclic Rate: ~850rpm


Bibliography:

The World’s Assault Rifles, G.P. Johnston & T.B. Nelson, (2016)

Die G11 Story, W. Story, (1993)

Full Circle: A Treatise on Roller Locking, R. Blake Stevens (2006)

The 5.56 Timeline, D. Watters, (source)

1985 HK Brochure on the G41 Series (via SAR Archive)

HK G41 Owner’s Manual (via SAR Archive)


Our thanks to the collection that holds this rifle for their kind permission to examine and film it. Please do not reproduce photographs taken by Matthew Moss without permission or credit. ©The Armourer’s Bench, 2019.

Stripping the HK G11

Our thanks to the collection that holds the G11 for the privileged and nerve-wracking opportunity to field strip it and take a look inside. If you’d like to know more about the history of the G11’s development you can check out our video and full blog on it here. Vic has done a great series of videos looking at the G11 and the other prototype rifles from the US Army’s abortive Advanced Combat Rifle trials – you can find those here.


In this blog we’ll take a closer look at some of the G11’s components, for a demonstration of dissassembly and and explanation of how the rifle works in principal check out the video above.

Firstly, lets take a look at the exterior of the rifle. The weapon has a box-like polymer coated outer shell. The shell is made up of three parts, with the butt assembly and forend locking into the centre assembly which includes the pistol grip, trigger mechanism and optical sight. The forend and butt are locked into the centre assembly by plastic locking tabs. While stiff and somewhat difficult to depress the tabs are reportedly prone to breaking.

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Left side view of the G11 (Matthew Moss)

Before we look at the G11’s internals lets take a look at the shell components. Here we can see the inside of the forend, we can see a metal (aluminium I believe) barrel tube into which the barrel slides.

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Close up of the the inside of the G11’s forend (Matthew Moss)

Below is a photograph of the rear of the centre assembly looking forward, the small white circle (sadly slightly out of focus) is the bushing the barrel protrudes through into the forend.

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The G11’s centre assembly houses a metal guide rail and magazine guide as well as the trigger mechanism (Matthew Moss)

Next we have a view of the inside of the rifle’s butt assembly. Note the scuff marks on the inside where the centre assembly has scrapped the plastic. We can also see the locking tab windows which are on the top and bottom of the butt.

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A view inside the G11’s butt stock (Matthew Moss)

Inside the butt we can see the ‘toothed wheel’ and ‘sealing gear’ which are turned when the cocking piece is rotated. These plastic pieces act directly on the action. Behind that is the gas escape valve, which will tap off excess gas if over pressure problems occur with the rifle.

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A close up of the sealing gear and toothed wheel that interface with the cocking handle (Matthew Moss)

The first step to disassembling the G11 is ensuring the weapon is clear by pushing the cleaning brush up into the breech.

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Close up of the G11’s cleaning brush, housed inside the pistol grip (Matthew Moss)

Lets now take a look at the rifle’s action up close, below we can see the G11 with its forend and butt assembly removed. Next to it is the breech cylinder and control disk.

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The G11 field stripped (Matthew Moss)

Here are some photos of the action from various angles:

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A view of the action from the rear. We can see the striker assembly, clamping plate, ejector lever and cylinder retaining catch (Matthew Moss)
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From the right side of the gun we can see the two gears which work the breech cylinder – the spur gear and the actuating gear (Matthew Moss)
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On the underside of the action we can see the rear of the clamping plate, the slide – which is slightly worn, and the sear projecting below it (Matthew Moss)

Here’s some close ups of the breech cylinder and control disk:

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The top of the control disk, which has to be removed before the breech cylinder can be (Matthew Moss)
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Underside of the control disk (Matthew Moss)
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Top view of the breech cylinder (Matthew Moss)
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A view of the square chamber which is a replaceable part which is held in the breech cylinder by a circular retaining spring – seen on the right (Matthew Moss)
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The base of the breech cylinder with notches where the actuating gear interfaces (Matthew Moss)

Here are some close ups of the various parts of the action:

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A close up of the rifle’s spur gear – which gives the G11 its almost clockwork appearance (Matthew Moss)
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Another close up of the underside of the action (Matthew Moss)
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Close up of the end of the barrel, with the square outline of the breech chamber visible – the G11’s caseless ammunition was rectangular but the projectile was round in diameter (Matthew Moss)
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Another shot of the rear of the action showing the striker / firing pin assembly and spring  (Matthew Moss)

According to the 1989 armourer’s manual, provided for the ACR trials, the G11 is made up of a total of nearly 450 individual parts. 144 of those make up the G11’s breech assembly.

With the breech and barrel assembly removed from the centre assembly here’s a diagram I put together showing most of the component parts of the G11’s action:

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G11 Breech & Barrel Assembly Diagram (Matthew Moss)

Next lets take a look at the G11’s barrel assembly with its recoil management system and gas piston:

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A bird’s eye view of the G11’s breech and barrel assembly, note the barrel markings (Matthew Moss)
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A side view of the breech with the cylinder and control disk in position (Matthew Moss)
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A view of the housing of the recoil mitigation system, on the other side is the gas piston system (Matthew Moss)

Finally, here’s a photo of the G11 broken down into its major component assemblies: magazine, forend, centre assembly breech & barrel assembly and butt stock:

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G11 field stripped (Matthew Moss)

If you enjoyed the video and this article please consider supporting our work here.


Bibliography

HK G11- ACR. Armourer’s Manual for Maintenance of Repair of Rifle, 4.92mm, ACR, March 1989 (source)

‘Rifle, 4.92mm, ACR’ Operator’s Manual (source)


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

Heckler & Kock MP5K Briefcase Gun

 

 

Officially designated by Heckler & Koch as the ‘Spezialkoffer’ or Special Case, the Briefcase Gun, sometimes referred to as the Operational Briefcase, is a clandestine weapon system designed for personal protection details. The ‘Special Case’ was introduced in the late 1970s offering the firepower of an MP5K in a concealed package which could be rapidly brought into action.

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A view of the case’s exterior (Matthew Moss)

While the MP5K is already a compact weapon that can be carried concealed under a coat or tucked under the arm, the Special Case, in theory, allowed the weapon to be carried in an instantly accessible way. One H&K leaflet stated that the case retains “approximately the same rapid readiness to fire” as an unconcealed submachine gun. The case had the added advantage of being able to be operated with just one hand.

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A view of the case open with MP5K mounted (Matthew Moss)

To build the brief case Heckler & Koch turned to Hofbauer GbmH, a German manufacturer that specialises in extrusion blow moulded protective cases for tools and equipment, to make the case body. The case is made from black plastic moulded over an aluminium body with a stainless steel locking clasps and a strip of silver trim tape around the lower half. Inside on the right hand rim of the lower half of the case is the case maker’s marking ‘Hofbauer Boss Flanegg’.

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Close up of the case’s Hofbauer markings (Matthew Moss)

Inside the case Heckler & Koch used a modified STANAG claw mount, with a modified release lever, that was normally used to mount optics on G3s and MP5s. The claw mount system holds the weapon in place and a firing mechanism connects a trigger in the briefcase’s handle to the weapon’s trigger inside. The weapon itself is an MP5K, the example we’re examining today has a ‘SEF’ selector and the contoured stahl G3 griffstück (pistol grip assembly). The MP5K was first introduced in 1976, reportedly developed following a request from the security detail of a South American head of state.

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The case’s HK MP5K (Matthew Moss)

The muzzle of the MP5K’s 4.5 inch barrel fits into a tube or shroud in the left side of the case. Below the weapon is a clip to hold a standard plastic MP5 cleaning kit. While inside the lid of the case there is a clip to hold a spare magazine.  The MP5K-PDW, introduced in the early 1990s, will not fit into the case as the muzzle and folding stock prevents it from fitting.

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A close up of the cases muzzle ‘tube’ and rubber muzzle cap (Matthew Moss)

The trigger in the case’s handle works through a series of linkages which connect it with the MP5K’s trigger. Pulling the external trigger upwards pulls an linkage forward which in turn acts on a pivoted arm which pulls the weapon’s trigger. The case has a built in safety on the left side of its handle. When pulled to the rear with the thumb it moves a blocking bar backwards and allows the trigger, inside the handle, to travel upwards to fire the weapon. There is some variation to the trigger mechanisms with a slightly dog-legged, rather than straight, trigger arm being introduced to allow the use of MP5Ks with ambidextrous selectors.

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The cases’s handle disassembled, showing the trigger mechanism (courtesy of Nicholas Chen)

Once fired the spent cases are deflected down into the body of the case and can only be removed once the case is opened to reload or remove the weapon from the case. There is no ejection system built into the case.

In addition to the case we have examined in this video/article, there is also another version based on a leather satchel-style briefcase, known as the ‘Spezialtasche’ or Special Bag. Instead of the moulded plastic case the MP5K is held inside a leather case with a ‘reach-inside opening’, which allows the user to put their hand inside the case and hold the pistol grip and operate the weapon’s controls. The gun is still held in the same kind of cradle claw mount but the leather case does not have the integrated trigger in its handle. The upper half of the case, held in place by four snap buttons, could come free of the lower section to allow the MP5k to quickly be accessed for reloading and removal from the claw mount.

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Late 1970s H&K product sheet for ‘Spezialkoffer’ or Special Case & leather ‘Spezialtasche’ or Special Bag (source)

As you would expect aiming a briefcase is no easy feat, the Special Case was intended for engaging targets at very close ranges or gaining initial fire superiority, suppressing a target long enough to either deploy the MP5K properly from the case or extricate the principal being protected. One of the major issues with the case is naturally limited access to the weapon which makes changing fire more, clearing stoppages and reloading impossible without opening the case – which can only be accomplished by opening the case’s two locking clasps, which in a contact situation would take precious seconds of fumbling.

Here’s what appears to be some vintage promotional footage showing the case in action:

 

A substantial number were sold, especially to Middle Eastern countries. During the 2003 Invasion of Iraq, the troops from the US 7th Infantry discovered a cache of 24 H&K Briefcases untouched, like new in their wrappings, bought by Saddam’s regime. Heckler & Koch continue to offer the case, two models are currently listed on their website: the original briefcase, now referred to as ‘Schießkoffer’ or ‘shooting case’, and a quick deploy ‘Zerfallkoffer’ case (offered for both the MP5K and the MP7) .

If you enjoyed the video and this article please consider supporting our work here.


Specifications (taken from H&K data sheet c.1984):

Case:

Case External Dimensions: 17.24×4.25×12.67in (438x108x322mm)
Weight of case without MP5K: 3.3 lbs (1.5kg)
Weight of case with unloaded MP5K: 7.72lbs (3.5kg)
Weight of case with MP5K + 60 rounds: 14.88 lbs (6.75kg)

Weapon – MP5K:

Length: 12.8in (32.5cm)
Weight (unloaded): 4.4 lbs (2kg)
Barrel Length: 4.5in (11.4cm)
Action: Roller-delayed blowback
Calibre: 9x19mm
Feed: 15 or 30-round magazines
Cyclic Rate: 900 rpm


Bibliography:

Full Circle: A Treatise on Roller Locking, R. Blake Stevens (2006)

The Gray Room, J. Phillips (2010)

‘HK Operational Briefcase: German design, MP5 included’,  Guns.com, C. Eger, (source)

‘H&K MP5K Briefcase: Luggage you can fire’, TFB, R. S., (source)

‘Review: H&K MP5K Briefcase And My Modifications’, TFB, N. Chen, (source)

H&K MP5 brochure c.1985, via Small Arms Review Reference Library (source)

H&K Special Case datasheet c.1979, via Small Arms Review Reference Library (source)

H&K German factory datasheet c. late 1970s for cases, via Small Arms Review Reference Library (source)


Special thanks to the collection that allowed us to examine and film the HK Special Case.

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.

If you enjoyed the video and this article please consider supporting our work here.


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

Heckler & Koch HK53

In 1968 Heckler & Koch launched the HK33, chambered in 5.56x45mm, to compete with Colt’s AR-15/M16. The HK33, and later HK53, used the same roller-delayed blowback action developed for the G3 in the mid 1950s. However, few major contracts were forthcoming with the German military opting to continue using the 7.62x51mm G3.

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Heckler & Koch HK53 (with ‘navy’ lower reciever) brochure c.1987 (source)

Due to the modularity of the HK33′s design users could replace the butt of the standard rifle with a collapsible telescopic metal stock. H&K also subsequently designed a carbine version of the full-length HK33, the HK33K with a telescopic metal stock and 12.7 inch barrel. In the mid-1970s H&K began development an even shorter version. The result was essentially an intermediate calibre submachine gun similar to the Colt Commando and the Soviet AKS-74U. H&K designated this new weapon the HK53, it used the same telescopic stock as the HK33K and MP5 and a cut down 11 inch barrel, the HK53 also utilised a polymer forearm similar to the MP5s.

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Contemporary promotional photos dating from 1985 (source)

Like the HK33, the HK53 fed from 25, 30 or 40 round box magazines. The weapon weighed just over 3kg (7lb), almost a 1 kg less than its parent rifle the HK33. Unlike the HK33, the HK53 has a four prong flash hider. A number of police forces and militaries adopted the HK53 for a variety of roles. Special forces units around the world including the British SAS, Royal Military Police Close Protection Unit and Royal Marines, designated the L101A1 in British service, who typically used it during close protection duties and operations involving close quarter battle.

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Contemporary promotional photo dating from 1985 (source)

As shown in various MoD Equipment Failure Reports dating from the early 1990s the HK53’s in British service suffered from repeated damage and failure of the carbines’ locking rollers. This issue arose when using a number of different ammunition types including brass cased blank ammunition (H&K recommend the use of their proprietary blank cartridges). Following a meeting between the Army Technical Support Agency’s Directorate of Engineering and H&K a new design for the locking pieces were developed. These changes “increased the roll of blowback force during the unlocking phase… in turn this will reduce the mean energy of the recoiling mass of breech block and carrier” this was intended to reduce bolt bounce. The Royal Military Police Close Protection Unit’s L101A1’s were also fitted with a new two stage buffer within a fixed stock. In British service the L101 was replaced by the L22A2 carbine and the L119A1 (C8 Carbine).

DSC_0843
HK53, stock collapsed, (Matthew Moss)

Due to its short length the HK53 also found itself pressed into the port-firing weapon role. Designated the HK53 MICV in this role the foregrip and stock was removed and a specially designed endcap and a spent case bag could be attachment. During its service life the HK53 went through a series of changes to furniture mouldings, buttstock types and fire selector options. It remained in production into the early 2000s, when Heckler & Koch replaced the HK33 and HK53 with the G36 and G36K.

If you enjoyed the video and this article please consider supporting our work here.


Technical Specifications (from 1987 H&K brochure):

Length (with stock extended): 76.5cm (30in)
Weight (collapsible stock, unloaded): 3.35kg (7.4lb)
Barrel Length: 22.5cm (8.5in)
Action: Roller delayed blowback
Calibre: 5.56x45mm
Feed: 25, 30, or 40-round box magazine
Cyclic Rate: approx. 700 rpm


Bibliography:

The World’s Assault Rifles, G.P. Johnston & T.B. Nelson, (2010)

Heckler & Koch HK33 & HK53 manual (source)

HK53 factory colour brochure, 1987, (via Small Arms Review Reference Library)

Itemised list of L101A1’s which suffered damaged locking rollers, MoD Equipment Failure Report, 15 Nov. 1994, (via Small Arms Review Reference Library)

Army Technical Support Agency report on receiver damage to HK53 and G3 rifles, 1996,(via Small Arms Review Reference Library)


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

Photos: Heckler & Koch G11 ACR

Here are a selection of external photographs showing the H&K G11 submitted to the US Army’s Advanced Combat Rifle trials in the mid-1980s. You can watch our introductory video featuring two G11s here.

Note: While this collection of images covers only the externals of the G11, rest assured that if and when we get the opportunity we will follow this up with hi-res photographs of the weapon disassembled!  UPDATE – We disassembled a G11!

1
Right side view of the G11, note the muzzle plug inserted into the barrel (Matthew Moss)
2
Left side view of the G11, note the small window in the magazine showing the follower spring (Matthew Moss)
3
Close up of the right side of the G11’s fire selector (safe – semi – hyperburst – full auto), trigger and grip which enclosed a ‘control brush’ used to check the chamber was empty and in cleaning (Matthew Moss)
4
Left side close up of the G11’s selector, trigger and pistol grip – note also the rifle’s designation,  serial number, presumably manufacturing date and calibre moulded into the weapon’s casing (Matthew Moss)
5
A view of the G11 from above – note the alignment of the magazine and the lack of later additional channels for spare magazines seen in some G11K2s (Matthew Moss)
6
Close up of the G11’s foregrip and sling loop and an empty magazine loaded into the weapon  (Matthew Moss)
7
Close up of the weapon’s rotating ‘cocking handle’and pressure valve, note the white arrow indicating the direction to twist the handle to cock the weapon – the plastic folding handle on this example has sadly broken off, a common issue with G11s (Matthew Moss)
8
Close up of the left side of the G11’s ‘central part’, as HK described it, into which the barrel and breech assembly slide (Matthew Moss)

Many thanks to the collection, which wishes to remain anonymous, that holds this example of the G11 for the opportunity to examine, photograph and film it.

If you enjoyed the video and this article please consider supporting our work here.


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