Hk 121 Heckler Kochs Hk 121
Military Guns

Heckler & Koch’s HK 121

[schema type=”product” url=”” name=”HK 121 Machine Gun” description=”As the successor of the MG3, The HK121 opens a new era of universal belt fed 7.62 mm x 51 machine guns. Compared to others, the gas operated HK121 offers an intelligent and contemporary build standard, with numerous technical and ergonomic innovations.” brand=”HK” manfu=”Heckler & Koch” model=”HK 121″ ]

At first glance this is a most impressive weapon. “Heckler & Koch” has been developing this machine gun since 2005, after it went through massive development management restructuring. MG4 5.56×45 was already being produced and the company wished to compete its offer with a universal machine gun of 7.62×45 calibre. Due to the events and experiences in Afghanistan, the Bundeswehr (German Federal Defence) required high firepower weapons that use old standard NATO calibre. First trials were done in 2010, in Meppen Military Technical Centre. After finishing touches, Bundeswehr approved the weapon confirming its safety and functionality, thus giving the green light for serial production.

Youngest Gun of the Family

Compared to MG3, HK121 has a distinctly different frame and a free barrel. To be frank, HK121 is visually very similar to MG4 and it is obvious they are members of the same family. HK121 is more than buffed up, larger calibre version of MG4 however. Unlike MG3 and MG4, where the housing is made from pressed sheet metal, HK121’s consists of two moulds of cast steel as well as a single adjoining block. These parts are then connected through special patented procedure, all of this should reduce the manufacturing expenses compared to the older methods. Also, this new procedure allows for better firearm accuracy. Although HK offers a warranty to the service life of the housing of 50,000 bullets fired, tests have shown that that limit is significantly higher. In addition, outer olive-brown varnish provides excellent camouflage.

Heckler Koch Hk 121 Heckler Kochs Hk 121

Old Belts Fit Just Fine

Another advantage of the new “Heckler & Koch” machine gun is its lower weight when compared to its predecessors. Depending on the model, it can weigh from 9.9 kg to 11.2 kg, making it much easier to carry and use than MG3. This is especially notable when it is being used during patrols and terrain sweeps. Its light weight makes shooting it standing up almost as easy as lying down. Designer have anticipated the use of M12/DM60 disintegrating belts. These machine guns easily use the hanging 250 rounds belt that by itself weighs 7 kg. Older 50 rounds metal D1 belts are also compatible with this weapon, despite the fact they were originally used by the Wermacht. HK however, does not accept responsibility for problems and malfunctions of the machine gun if those old belts are used.

Barrel of Pride

Robust, cold forged barrel covered with a special protective layer looks quite imposing. For the sake of comparison, during normal firing tempo, the MG3 barrel can fire around 400 DM151 steel core rounds. G-8 rifle can fire around 1000 shots of the same ammunition, while the barrel of the new HK121 can endure 1500 rounds in frequent firing regime. Simple math tells us that HK121 barrels will last over four times longer than those of MG3. “Heckler & Koch” offers barrels in three lengths: standard 550 mm, infantry 460 mm and mounted 663 mm.

There is significantly less danger from the barrel overheating or accidental firing of the bullet in overheated chamber; it can happen only after the 300 DM111A1 rounds are fired and if the ambient temperature is greater than 20 ° C. HK121 does not require frequent barrel replacements as was the case with older machine guns. For example, MG3 barrel mist be replaced after 150 rounds of live ammunition. HK121 on the other hand, needs it only after 200-250 rounds. Not so much because of the overheating, but to preserve barrel longevity. If recommended firing limits are observed, the barrel can last much longer. The barrel can be replaced quickly and easily, even without help. The replacement procedure can be completed in just a few seconds without the need for protective gloves.

Ammunition is belt fed, with the belt being fed from the left side of the weapon, same as with MG3 and MG4. Unlike MG3, that uses delayed recoil and has a locked seal with a rotating bolt and a gas piston. This operating system has proven its worth on the FN MAG machine gun, so it is no surprise HK used it as early as with MG4.

Hk121 s Heckler Kochs Hk 121

Rate of Fire and Accuracy

While the effective combat range of HK121 is 600 m, when mounted it can shoot accurately up to 1200 m. “Heckler & Koch” company guarantees the shooting diameter of 30 cm, in single fire mode at the distance of 100 m, with 10 fired rounds of soft core DM111A1 ammunition. For the sake of comparison, MG3 would make a 59 cm diameter at the same distance. HK121 has made a significant improvement concerning machine gun accuracy. Rate of fire is lower than the incredible 1200 rpm of the MG3. HK121 can fire in three different modes: 600, 700 and 800 rounds per minute. Rate of fire can be changed quickly and without any special tools, just by changing the amount of gas released. The slower rate of fire significantly increases both accuracy and the service life of the weapon, making it more than a worthwhile compromise; especially if one takes into consideration reduced bullet consumption, often a critical factor in combat situations when an infantry group needs to hold position for an extended period of time.

Ambidextrous selector lever

Handling this machine gun is easy not just for shooters who have experience with MG4, those used to MG3 should not have any trouble either. Loading mechanism is similar, with the caveat that handling HK121 seems easier and more comfortable because it requires less strength. First you need to pull the locking bolt back, and then release it so it slides forward. Next, you need to open and lift the housing cover and insert the belt into the slot designed for it. Then you just need to close the cover and you are ready to open fire; but only if the safety is off. Unlike MG3, HK121 has an ambidextrous selector lever and it can be easily turned off or on, whether it’s loaded or not. This is the first machine gun in the world to offer that capability. For additional security, it uses an indicator that shows the loaded state, if there’s a single bullet in the barrel this indicator pokes out of the housing cover, that way you can both see and feel it. Also, if a bullet jams in the barrel, the next one will force it out without the barrel bursting in the process. And most importantly, the weapon continues with normal operation afterwards.

Heckler Koch 121 Heckler Kochs Hk 121

Adaptable for any Situation

Housing cover of HK121 has long NATO STANAG rails, which allow for mounting of all mechanical and optical sights, including night vision accessories. The cover itself is strong enough to bear significant weight, i.e. everything you can think of putting there. However, there is more to it than rails and sights, new H&K machine gun can adapt to various personal preferences and requirements. Various barrels, folding and telescopic stocks, armguards (with or without levers), bags for empty bullet casings and bags with rolled 50, 60, 100 or 12 rounds ammo belts. So, anyone can make an optimum configuration that suits their needs. In addition, the designers have resolved the problem with easily misplaced small parts.

Old MG3 kits can still be used on the new HK121. If you replace the belt feeder, you can use the plastic box with 120 rounds or the ammo drum with 50. Also, HK121 can be mounted on all mounts meant for MG3, even vehicular ones. Besides that, H&K offers the machine gun in the mounting variant, with a far more resilient barrel, greater muzzle velocity and range of up to 1500 m.

Future of Infantry Weaponry

It is certain that no long time MG42/MG3 shooter will give up their gun easily and replace it with the new one. Many veterans were loath to use MG4, even when it was meant to complement rather than replace the MG3 But this weapon is a different story, it is similar enough to MG3 and almost identical to MG4, excepting the larger calibre, that it should not be a problem for old time veterans to adjust, when we add many improvements and new cutting edge enhancements that are likely to become standard for infantry armaments in the future, the decision seems like no brainer.

Primary Weapons Systems is another firearms manufacturer dedicated to quality and state-of-the-art technology.

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author avatar
Jeffrey Stevens
Jeff is a passionate collector with curated selections of historical firearms, from derringers to Civil War cannons. Besides collecting them, he also loves researching and writing about them.
January 31, 2013
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