History of the Heckler & Koch 40mm Grenade Launcher

History of the Heckler & Koch 40mm Grenade Launcher

The HK M320 40mm grenade launcher.

Until recently, the field of 40mm grenade launchers was almost exclusively dominated by the M203.  With the recent adoption of the Heckler and Koch M320 by the U.S. Army, a look back at Heckler and Koch’s legacy 40mm systems is in order.  First designed in the late 1950’s, the 40mm grenade system was a stop gap system to bridge the distance between grenades thrown by hand, and the employment of light mortars.  Hand grenades are limited by the distance the infantryman can throw the grenade, typically about 25 meters.  A mortar is capable of dropping rounds as close as 60 meters from the firing position, but the weight of the system and ammunition present logistical and load bearing issues for light infantry.  Clearly, a smaller and lighter weapon system was needed to bridge the gap.  Enter the 40mm grenade.

The HK69: the Original H&K Grenade Launcher
The HK69 grenade launcher is a stand alone, single-shot, shoulder-fired, breech-loaded weapon.  The receiver incorporates the barrel assembly, firing system, and trigger mechanism.  Configured with a rifled barrel, the barrel is hinged at the front of the receiver and rotates upward and away from the receiver, much like an over/under shotgun.  Like a shotgun, the oversized latch to the rear of the receiver (and what appears to be the weapon’s hammer) is actually the barrel release mechanism.  By pushing the barrel release latch to the rear, the barrel is unlocked from the receiver, and springs open under spring tension.   The system lacks an ejector because one is not needed; the additional engineering and weight was deemed unnecessary for a single shot weapon.  Instead, the barrel breech is cut to allow the user to pull the spent cartridge from the breech of the barrel.  This design element has continued throughout the HK 40mm system design, and can still be seen within the current M320 design.

Weighing in at 5.75 pounds, the HK69 distinguished itself from the XM148 and the M203 in that it utilized a break action, similar to a shotgun.  This design proved fruitful, and has lived on as one of the most useful designs in 40mm systems.  The M203 was limited to a round approximately 5.25 inches in length – if the round was any longer in length, the M203 receiver interferes with the loading of the 40mm round in the M203 barrel.  Unlike the M203, the HK69 has no issue accepting oversized 40mm rounds.  Because the barrel swings upwards and away from the receiver, the barrel is not obstructed by the receiver.  This design element has also continued to the present, and can be seen with slight variation within the Heckler and Koch M320 weapon platform.

The safety mechanism on the HK69 is a lever system, on the left side of the receiver, with large markings to show whether the weapon is rendered safe, or ready to fire.  The safety blocks the trigger bar from releasing the hammer; in this manner, the weapon may be safely carried loaded, hammer cocked, with the safety on.  Not one to trust mechanical safeties, potential users may consider carrying the weapon in Condition 2 (hammer down on a loaded chamber) as a better alternative.

The HK M320 mounted on an HK 417 rifle. The HK M320 is interchangeable between rifles without special mounts or hardware. (Photo courtesy of Heckler and Koch.)

The hammer on the HK69 is external to the receiver and is exposed for manual manipulation.  When needed, the hammer can be quickly cocked, rendering the weapon ready to fire.  In the event of a misfire, the weapon can be quickly re-cocked by engaging the hammer.  The trigger on the HK69 is surprisingly light.  Given the design as a single action trigger, perhaps the responsive trigger should not be surprising.  When shooting the family of Heckler and Koch 40mm weapons, the HK69 had the best trigger system, far exceeding the double action only triggers found on later Heckler and Koch systems.

The HK69 utilizes a polymer pistol grip, and a lightweight tubular telescoping metal stock.  Sling swivels are available for use with a sling.  The system is strictly a stand-alone unit, and cannot be mounted to a host weapon in the same manner as the HK79 weapon system, or other future HK 40mm systems.

Operation of the HK69
Loading and unloading the HK69 is intuitive and easy.  To open the barrel, grasp and rotate the oversized barrel release mechanism to the rear.  The barrel opens under spring tension.  Loading the weapon is as easy as dropping the desired 40mm round into the breech of the barrel.  Unloading the weapon is equally easy by utilizing the semi-circle relief cuts within the breech to grasp the cartridge base.

The weapon is cocked by retracting the hammer at the rear of the weapon.  The manual safety on the left side of the receiver should be pushed to the “fire” position.  The weapon is now ready to fire.

Two sight systems are employed on the HK69.  The first system utilizes a small, fold down blade sight capable to engaging targets at 50 to 100 meters.  For longer range accuracy, a folding ladder sight allows the user to engage targets out to 350 meters.  With a little practice and experience, it is possible to engage targets beyond the listed maximum range.

Final Analysis
Potential downsides of the HK69 included the all metal interface – the weapon seemed significantly heavier than any other 40mm grenade system, save for perhaps the HK79, when mounted to a G3 rifle.  The steel receiver has a tendency to get extraordinarily hot when exposed to desert firing conditions.  Presumably, the steel receiver would be equally cold if exposed to sub-freezing temperatures.  The same issues were not observed when test firing other systems.  Other downsides included the single-action only trigger.  Although the single action trigger was extraordinarily crisp when compared to other 40mm systems, the weapon has no provision to fire as a double action.  In the event the shooter forgets to cock the weapon, the weapon will not fire – the trigger simply releases the hammer – the trigger will not cock the hammer if the hammer is down.  Adopted by the German army in 1974, the HK69 was popular within the European community, but saw limited commercial success in the United States.  As a first generation 40mm weapon system, the HK69 is highly effective, easy to use, with the fire control mechanisms intuitive to most shooters.

The author test firing the HK 79 grenade launcher.

The H&K HK79: Competitor to the American M203
Partially based upon the HK69 design, the HK79, together with the XM148 and M203, brought significant firepower to the individual infantryman.  No longer limited to the engagement distance of hand thrown grenades, the individual infantryman could use his rifle as a mobile platform for indirect fire.  Similar to rifle grenades of World War II, the 40x46mm grenade system offered a larger payload and more advanced safety systems.  More importantly, rifle grenades of World War II relied upon blanked ammunition to launch grenades down range.  With the advent of the 40x46mm grenade systems, the individual infantry soldier could engage the enemy with a 40mm grenade with follow on fire from his rifle.  There was no longer a need for the soldier to carry ball and grenade launching rifle ammunition.

The HK79 was the German response to the M203.  Designed to be attached to German battle rifles, the HK79 was most commonly seen mounted to the G3 and HK33 model rifles, but could be adapted for mounting to most European designed rifles.  Because the system was based upon the design attributes of the HK69, there are design commonalities between the two systems.  Most notably, the HK79 is made primarily of steel, resulting in a heavy addition to any battle rifle.

The HK79 grenade launcher is a single-shot, shoulder-fired, breech-loaded weapon.  Like that HK69, the receiver incorporates the barrel assembly, firing system, and an unusual trigger mechanism.  Configured with a rifled barrel, the barrel is hinged at the front of the receiver.  Unlike the HK69, the HK79 barrel rotates downward and away from the receiver.  The practical effect however is the same – the barrel extends away from the any obstruction created by the receiver, allowing extra length 40mm rounds to be easily chambered.  Similar to the HK69, the barrel is released via an oversized latch on the left side of the receiver.  By pulling the barrel release latch to the rear, the barrel is unlocked from the receiver, and allows the barrel to open under spring tension.  Like the HK69 (and all HK 40mm systems) the system lacks an ejector – the barrel breech is cut to allow the user to pull the spent cartridge from the breech of the barrel.

Operation of the safety is achieved via a cross-bolt manual safety catch, a traditional round push through switch installed on the receiver, forward of the cocking mechanism.  The “safe” and “fire” positions are marked with red and white rings respectively; the weapon can be loaded and cocked with the safety set at either position.  Unlike the HK69, the fire control mechanisms on the HK79 are entirely different from any previous or subsequent 40mm grenade launcher.

Replacing the external hammer of the HK69 is the Hk79’s horizontal T-grip, at the rear of the receiver.  Similar in size and shape to the charging handle on an M16 rifle, the HK79 hammer is set by retracting the charging handle to the rear.  The charging handle also has the effect of resetting the trigger.  Like the HK69, the system can be re-cocked without unlocking the breech, in the unlikely event of a misfire.  In this respect, the HK79 is similar to the failed American XM148, which also used an external handle to charge the weapon.  However, the HK79 system is much more refined than the XM148 system as would be expected from German engineering.