Notes from the HK Grenade Launcher Armorer Courses (Part 1)

[Marine0303]

Due to the amount of information provided and the word count limit for posts on this forum, I have split this report up into two separate posts. Part II: HK High Velocity Grenade Launcher: GMG, can be found here:

Notes from the HK Grenade Launcher Armorer Courses (Part 2)

Part 1: HK Low Velocity Grenade Launchers: HK69, HK69A1, MZP1, MZP1A1, HK79, HK79A1, AG36, GLM, M320, HK169 and HK269

This past week, I completed the last of the current Heckler and Koch Armorer Courses. A process that I spread out over a three year period, in some ways, I saved the best for last. Four the last four days I completed the HK Grenade Launcher Armorer Courses, covering both their low velocity and high velocity offerings. I’ll begin with the earliest models, which were covered on the first day, the HK69, HK69A1 and MZP1.

These three variants of the same basic design represent stand-alone, single-shot, break action launchers, firing a wide variety of 40mm x 46 caliber low velocity cartridges. Designed and produced during HK’s delayed roller locking bolt gun period, these launchers share similar rolled and stamped steel receiver manufacturing. Their simplicity of design, robustness, reliability and safety are why these are still found in active use across the US and foreign countries.

First came the HK69. The designation does not represent the year it was designed or entered service, but an early HK weapon categorization. The numerical system used at the time relied on the numbers 1-9 to represent different types of weapons as well as different calibers of ammunition. The first number, 6, represented stand-alone grenade launcher, while the second number, 9, represented the 40mm x 46 caliber cartridge.



The A1 designation reflects an upgrade over the original model, with three minor modifications. First, the barrel elbow spring, which pivots the barrel open and closed, was upgraded to a more robust version. Second, a striker assembly (hammer) safety was added (more on this later). Lastly, on the HK69, the rear sight screw was drilled and tapped completely through the top of the barrel. It was found that over time, the overpressure associated with firing the weapon was causing the rear sights to shift. In the A1, the rear sight screw did not penetrate through the barrel, thus eliminating that issue.



Next came the MZP1 or Multi-Purpose Pistol. Functionally, it was identical to the HK69 except for its markings and its sighting system. Intended to be used in a law enforcement role, where the need to launch high explosive rounds at distance was not viable, the long range ladder sight was removed and in its place, a short range flip up rear sight covering ranges from 50 to 100 meters. The only other difference between the models is the buttstock. The HK69 and HK69A1 both have a convex rubber recoil pad, equal distance on each end from center line. This allows the shooter, when aiming through the tall ladder sight, to roll the weapon through the full range of motion, while pressed into his shoulder. Since the MZP1 utilized a much smaller sighting system and therefore less of a need to roll the weapon, the top portion of the recoil pad was significantly reduced. As with the HK69A1, an A1 variant of the MZP1 was also produced, with the same upgrades. Below, you will see an example of this weapon and the date code markings show that this weapon was produced in 2002.



Since we’re on the subject of the sighting system, I’ll go ahead and cover that in depth here. Shown below is the dual sighting system of the HK69A1. As you can see, at the base is the flip up short range sight. In its lowered position, it incorporates a three dot, partridge system (in tandem with the single dot of the front sight post) and represents the 50 meter setting. When flipped into the up position, the shooter must elevate the barrel and front sight slightly to utilize the 100 meter setting. For distances beyond 100 meters, the ladder sight is extended and you can see the notches in which the front sight is placed within at ranges for 150 to 350 meters. This large amount of barrel elevation is a factor of the significant arc of flight pattern that the 40mm x 46 caliber cartridge travels when fired. The final two dots at the very tip of the ladder sight are luminescent and correspond with a single luminescent dot, which is blocked in this photo by the 250 meter setting on the ladder sight (if you look closely, you can see the base of that sight midway along the barrel just under that 250 meter setting. This section of the sighting system was used at night for firing high angle flare projectiles. Anyone who has ever served in the infantry and conducted illumination supported live fire attacks will appreciate this feature.



Here are close up photos of the rear sight in the folded down, 50 meter setting and then the raised 100 meter setting.





Shown below is the rear sight of the MZP1A1. The short range sight remains the 50 meter setting, but in this photo of the flipped up sight, you can see two three dot, partridge options, the lower one designating 75 meters and the higher position for 100 meters. The sight base midway down the barrel does not contain the luminescent single dot of the HK69A1 for the flare sighting system, again, as the MZP1A1 was not intended to fill that role. Instead, a blank filler fills that position.



Sight adjustments for both windage and elevation are made from the rear sight, in a similar fashion as that of the G3/MP5 series. Utilizing the diopter sighting tool (phillips head portion), on the top screw for elevation adjustments and the side screw for windage adjustments. Each click on either screw, in either direction, moves the strike of the round approximately 2 inches at 100 meters.

Also shown below is the barrel assembly completely disassembled; a very simple design.



The weapons are operated by a single action trigger system, requiring the user to first cock back an exposed hammer. A very stout trigger pull of between 13 and 20 pounds is the result of a heavy hammer strut spring, but was incorporated to ensure reliable ignition without the fear of light primer strikes. 40mm x 46 cartridges utilize heavier primers than conventional rifle or pistol cartridges, which require more force to detonate.

Mounted in line and forward of the hammer is the barrel locking lever. Actuating it, releases the barrel for a top open break.

The stock is a very simple but robust design. Simply rotating the recoil pad 90 degrees and pushing forward collapses the stock to a space under the barrel. Then rotating the recoil pad back 90 degrees locks the stock in the closed position. To extend the stock, you just reverse the process.

As with all HK designs, safety is a primary factor. Besides the ambidextrous safety selectors, which when set in the safe position block the rearward movement of the trigger, two additional features prevent accidental firing.

First, a spring-loaded striker assembly (hammer) safety (part of the A1 upgrade) is positioned between the rear of the breach and the hammer. When the hammer is cocked, the locking plate is pushed up, where it blocks the hammer’s striker assembly from making contact with the primer of a chambered cartridge by blocking the firing pin hole into the breach. Only when the trigger is pulled is the locking plate released and under spring tension does it drop out of position, allowing free forward movement of the hammer.

Second, a drop safety within the trigger assembly prevents the weapon from accidental hammer release by drops or blows in case the hammer is cocked and the safety is off. At rest, the drop safety pivots behind the trigger and blocks its rearward movement. Only when the trigger is actuated does the drop safety pivot and allow the trigger and trigger bar to begin movement and out of contact with the pivot point on the sear.

Most of you HK fans are familiar with the markings that are placed on each of the weapons. A familiar sight is the “Eagle N”, a quality control stamp, with the N representing Nitro Cellulose or smokeless powder. In the photo below, an additional and rarely seen marking has been placed just to the right of the “Eagle N”. This “Eagle J”, with the J representing the code for repair or modification, shows that at some point this particular weapon was sent back to HKO for some sort of work. A deeper research utilizing the serial number would tell that tale.



Also shown above are the half-moon cutouts on the rear of the barrel, which were incorporated to more easily remove a spent cartridge casing after firing, especially when gloves are worn.

As with all of the HK weapons, I am always impressed with the tools and gauges that are produced to support and maintain the weapons. Shown below are several of the gauges for the HK69 series, the firing pin protrusion gauge, bore erosion gauges and the headspace and timing go and no go gauges. The first checks to ensure that the weapon does not have too much or too little contact from the hammer to the primer. Too much can make a very bad day and too little can cause light primer strikes. Neither is something you want with sensitive fuse munitions. The bore erosion gauges check to ensure that the barrel is still within spec and it is incredible how far the gauges would have to pass down the barrel before it was deemed out of spec; again an obvious nod to how well HK produces barrels. The last gauges ensure that the breach face is set properly to support the cartridge.



Though not covered in detail during this course, I would be remiss if I did not also discuss another rare grenade launcher system from roughly the same period, the HK79 and HK79A1. Again, in the weapon designation code system of the time, the 7 represented attached grenade launcher and the 9 represented 40mm x 46 caliber cartridge. These under-slung launchers were based loosely off the HK69, but used in a similar format as the US designed M203. The HK79 was designed for use with the HK G3 and originated from a Norwegian request. The HK79A1 followed and was designed for use with the HK33 and later G41 rifles. Both systems are very simple to mount. You simply remove the standard handguard, and put the launcher in its place, held simply by the rear area of the barrel, against the rifle’s receiver and the single takedown pin at the front. Sadly, both systems are also awkward in nature, at least in my opinion. Unlike the M203, in which opening, loading and closing the breach also cocks the weapon for firing, the HK79 and HK79A1 require the weapon to be cocked separately.

I was able to locate a HK79 and HK79A1 in the Gray Room and mounted the HK79 on a G3 in order to run it through a function check. The photos below will illustrate the following.





Just forward of the magazine and magazine well on the G3 is the cocking lever for the HK79. Horizontally T-shaped, you simply pull it backwards slightly to cock the weapon. Then, just forward of the cocking lever, and horizontally mounted is a push through safety, similar to that found on a Benelli M1 Super 90. White paint on one side and the easily identifiable red marking (“you see red, you’re dead”) on the other. Forward of that and mounted on the bottom of the launcher, is the barrel release lever. Actuating it swings the barrel open below the safety and cocking lever. Now here is where the awkwardness really comes into play. Unlike all other sighting systems, which are positioned on the left side of the weapon, on the HK79 and HK79A1, these are found on the right side of the hand guard, a front post and rear ladder set both flip up, but the shooter is then forced to look over the right side to aim. This is further complicated by the fact that the trigger is on the left side above the barrel, a push button mounted midway along the length and easily misrepresented as a barrel release lever. I found that operating this weapon was about the least intuitive of any HK design I have encountered, still an interesting design that saw service with several countries and which lead to the next launcher in my training.

Day two of this Armorer Course had us transitioning, much as HK itself had done from the tried and true stamp steel weapons, to the production utilizing revolutionary space age polymer and aluminum construction. For us, this began with the GLM or Grenade Launcher Module, the next generation stand-alone and weapon mounted low velocity grenade launcher family. This actually covers a wide range of variations, the GLM, AG36, M320, HK169 and HK269, but all are just slight modifications of the basic model.

So, we’ll start with the G36 program, which called for a capability to mount a grenade launcher to the family of weapons (specifically the G36 and G36K). Like the G3 and HK79 program before it, HK designers created a system where the standard forearm was removed and the AG36 was replaced, held in place at the rear by niches in the rifle’s receiver and at the front by a retaining pin mounted through the barrel mounted gas block or, in those rifles that did not have this unique gas block, a gas block adapter mount.

In this photo, you can see the mounting point on a standard G36 barrel.



And in this photo, you can see the adapter mount for this G36K.



Our training primarily focused on its successor though, the GLM, so I’ll cover this in more depth. The GLM, with almost three inch shorter barrel than the AG36, is an incredibly lightweight, modular and simple design. Simple to produce, simple to maintain and simple to operate.





The most unique feature of the GLM is its modularity. Though the weapon itself, barrel and trigger assemblies, are the same, it is the top receiver that allows maximum flexibility. Though shown above in stand-along format with extendable stock option, HK designers put great thought into its design and provided multiple mounting positions and mounting inserts. Shown below are mounting inserts for the M16 with standard forearm, M16 with Knights Armament Company RAS, M4 with standard forearm and M4 with Knights Armament Company RAS.



Here you can see the GLM top receiver with the standard forearm M4 inserts (front and rear) and then with the GLM mounted.





Next, is the GLM top receiver with the M16 with the Knights Armament Company RAS inserts (front and rear) and then with the GLM mounted.





And here, you can see the GLM mounted on the M4, M16, HK416 and then the AG36 mounted on the G36. Now that the majority of G36 rifles have been outfitted with new picatinny forearms, we are seeing the AG36 replaced with the GLM as well, utilizing an updated picatinny mount.



Another neat feature of the GLM, which is mounted into the top receiver, is an adjustment tool. This allen wrench, which tucks away in a recess at the rear of the receiver, has allen head sizes on either end for use in adjusting the large and small screws of the weapon. Specifically, if you want to change the mounting option on the top receiver, you use the large side. If instead, you want to adjust the sights, you use the small size.



That leads us to the sights. Like the HK69 that preceded it, the GLM incorporates a ladder sighting system. A small flip up front sight and rear flip up ladder sight are housed within a mount which can be positioned on either the left or right side of the GLM, depending on the desires of the user. Simply removing four mounting screws, reversing the orientation and remounting the screws is all it takes. The photo below shows me with the weapon’s allen wrench mounted in the front sight and a torque wrench (used simply for efficiency) at one of the take down points.



This next photo shows the sighting system now mounted on the right side of the GLM.



Again, placing the front sight within the partridge recess of the corresponding rear sight distance will allow a shooter to engage targets from 50 to 350 meters. Elevation changes are made from the front sight, with one 360 degree turn in either direction moving the strike of the round approximately 13 inches at 100 meters. Windage changes are made from the rear sight, with the same deviations.



You might ask, what is the difference between a GLM and the M320, in use with the US Army? Besides the designation markings, the main difference for the M320 is the requirement and adaptation to mount the Day/Night sight from L3; not something usually seen in use after all. A hefty procurement of approximately 45,000 units by the US Army, to replace their aging M203s, the Marine Corps is also debating jumping on that contract as well.

The other variants of the GLM are the HK169 and HK269. Functionally the same, with the main difference being that these weapons are stand-alone launchers, with no capability to be mounted to a weapon. The original HK169 was offered with the same G36 folding stock. It even has the small clip on the right side of the receiver with which to hold the stock in its closed position. But by simply drifting out the stock pin, you can replace that stock with any of the upgraded G36 stock options.





The HK269 is a product improvement, which incorporates a loaded chamber indicator and the ability to set the weapon up to either open from the left or right side. All previous variants of the GLM only opened from the left.

Unlike the HK69 that preceded it, which was single fire operated, requiring the user to cock the hammer back before firing, the GLM uses a double action trigger system. The major benefit of this trigger system is that the weapon is cocked and fired with one pull of the trigger and if the chambered cartridge fails to fire on the first strike, the user can simply pull the trigger again. With a weapon, like the M203, the user would have to open the breach, careful not to eject the cartridge, and then reclose the breach, in order to recock the weapon before a second shot could be attempted.

Again, the trigger pull is very heavy, the result of a very stiff hammer strut spring, and the need for a harder strike on the primer of the 40mm x 46 caliber cartridge. With practice though, you get used to its heavy nature.

Like many of their other products, ambidextrous controls are present on the GLM, with both safety selectors and a barrel locking lever, which can be operated from either hand.

Safety, as always, is a primary focus in the design. The safety levers, when set on safe, through a position on the safety axle, block the rearward movement of the hammer to cock and fire. Likewise, a drop safety prevents accidental firing by blocking the forward movement of the hammer assembly until the trigger is pulled, sweeping the drop safety out of position. A hammer/striker block, which pivots with the movement of the trigger bar, also prevents the hammer/striker from penetrating into the breech face until the trigger is pulled. Finally the barrel locking lever serves double duty to prevent out of battery fire. A notch in the side of the barrel allows the rear portion of the barrel locking lever to rest within it when the barrel is closed and completely in battery. If the barrel is not fully in battery, the barrel locking lever is forced down and in that position, blocks the rearward movement of the trigger.

Each also GLM comes with a barrel cover. Tethered to the weapon by a short length of red cord and designed to protect the barrel, especially in dusty environments, it is a “shoot-through” item. Actually, the over-pressure associated with firing a round would blow the cover off before the actual cartridge ever made contact with it.

A picatinny rail on the bottom of the receiver offers the ability to mount different types of forward grips. Having something to grip on the front of the weapon really helps when shooting in the stand-alone format, which is how most of the users these days prefer to employ the GLM. Though mounted on a rifle may look good, it adds quite a bit of weight to the combined weapon, as well as offsets the overall balance. Many SOF units carry the GLM on a bungee type sling or in a specially designed holster, only drawing it when additional firepower is needed.



Breaking down the GLM to its individual parts and putting it back together is relatively simple. Of course, this is aided by several unique HK tools, without which the job would be much more complicated and possibly painful. Shown below is a combination tool and carrier for use in disassembly and reassembly of the trigger mechanism. From one side, it appears to be just a plastic box.



Yet, from the other side and opened, it divulges several smaller tools (two small punches, a combination punch and roll pin holder, an assembly pin and a hammer strut assembly/disassembly tool) and then fits around the grip of the trigger assembly.



Here, with the tool still in place in the grip, you can see the hammer strut assembly/disassembly tool alongside of the recently removed hammer strut and hammer strut spring.



And here, is a tool (I don’t even want to know how much this costs) designed to assist in reassembling the barrel stop pin, axle and spring.



Lastly, I always enjoy the unique cutaway representations that are part of the HKO’s Apprentice Program. The GLM did not disappoint; this model with the special titanium stock option that was designed for a special customer. The left side view shows a chambered dummy round and the trigger mechanism, with the heavy hammer strut spring, trigger bar and sear.





In this photo, you can see the hammer/striker assembly at rest and where it moves to make contact through the breach face.


Part II: HK High Velocity Grenade Launcher: GMG, can be found here:

Notes from the HK Grenade Launcher Armorer Courses (Part 2)

[Marine0303]

Digging back through old photos, here is a picture taken during combined training in Germany between US Marine Force Recon and German KSK, utilizing the HK69A1 to mark for close air support, dropping inert munitions.

[AGG]

Thanks for the excellent review and pics!!!

Tony

[skullbox]

I like seeing the pictures of some internals that are very similar to parts used in small arms. I saw what looks like a longer "UMP barrel pin" and slightly shorter "UMP stock pin." Another thing that looks the USP lockout key and a spring that looks like a UMP hammer spring. Great pics and thanks for sharing this as most of us will probably never see these in the flesh.

[Marine0303]

I like seeing the pictures of some internals that are very similar to parts used in small arms. I saw what looks like a longer "UMP barrel pin" and slightly shorter "UMP stock pin." Another thing that looks the USP lockout key and a spring that looks like a UMP hammer spring. Great pics and thanks for sharing this as most of us will probably never see these in the flesh.

Agreed, it has been fun as I have progressed through my training and experience to see what parts and functions have carried over from one weapon to another. Sometimes, unexpectedly, you get pleasantly surprised.

[Hami]

And there it is, the coolest picture you have ever posted!