HK416 Rifle System

 HK416 Rifle System

Caliber :　5.56 × 45mm NATO

At the 2004 Gun Show held in Las Vegas, USA on February 11, HK exhibited several new products. In addition to the XM8 and P2000SK, there was also a series of carbines collectively called "HKM4" (note: not HK's "M4", but "HKM4") . This weapon is actually a modification of the M16 series rifles. It was named HKM4 instead of HKM16 probably because the name M4 has more commercial value. At that time, many companies produced and sold rifles with similar appearance and names to M4, which made Colt extremely dissatisfied. In April 2004, it first attacked HK and Bushmaster and filed a lawsuit in court. Colt won the lawsuit against HK, and it may be for this reason that HK was forced to abandon the name "HKM4" and change the name of this series of products to "HK416", where "4" probably refers to M4 and "16" probably refers to M16.

HK416 was re-launched in February 2005, and a new rail handguard was adopted, making the appearance of HK416 quite different from the original HKM4. However, on December 8, 2005, a federal district court judge in Maine ruled in favor of Bushmaster, which resulted in Colt losing the exclusive right to use the "M4" trademark. But for HK, this result is meaningless. Now HK's promotional materials do not even mention the HKM4 prototype gun at all, and only call it the "416 prototype."

The earliest HK416 promotional image and logo. This model is now only called the 416 prototype.

HK M4's gas system. Since the gas system takes up a lot of space, the double-layer aluminum heat shield in the upper handguard was changed to a single-layer one.

HK416 gas system

According to the information provided by HK American company's official website, the development plan of HKM4 started in 2002. But according to the project leader of the plan, Larry Vickers, who retired from the Delta Force (officially referred to as CAG, i.e. "Combat Application Group", see my previous article " Delta Force - Rumors and So-called Insider ") , the HK416 project can be traced back to 2001. At that time, Jim Schatz, who was in charge of military products at HK, happened to visit the Delta Force for an unrelated matter. Larry Vickers learned from him that after HK improved the reliability of the British SA80 (L85/L86) weapon system, it came up with the idea of ​​improving the M4A1 carbine, and at that time the Delta Force put the issue of improving the M4A1 carbine on the agenda.

The M4 series carbines, which are widely used by special forces, have always been controversial. The family is popular for its good ergonomics and high shooting accuracy, but its reliability in harsh environments is always criticized - if you can always keep the gun lubricated, use only military-spec bullets (such as M885 and M193), use a magazine in good condition, and shoot in semi-automatic mode, the M4 series carbines will work well. But when you continue to shoot in full-automatic mode for a long time and do not maintain these guns diligently, you will be in trouble. However, the battlefield environment determines that special forces often have to use the gun beyond the limits of the design. In addition, many M4A1 carbines equipped by the US special forces at that time were also facing the problem of over-service, that is, even if they did not replace new weapons, they needed to purchase a batch of new M4A1s. Therefore, the Delta Force planned to take this opportunity to try to choose a new gun.

The Delta Force spent a lot of money to test any short weapon they could find, including various AR-style short rifles and non-AR weapons such as G36C and SIG SG552, and finally came to a conclusion: no weapon can meet all their requirements-perhaps some models perform well under certain conditions, but not suitable for all situations. Of course, another reason may be that they are already accustomed to AR-style weapons and cannot fully exert their combat skills when using another weapon. Shortly after these studies began, Larry Weeks discovered that HK was considering providing a product improvement project for the M4 carbine, and HK hoped to get the US government model M4 series carbine for analysis and improvement, just like their previous SA80 project plan. Larry Weeks reported to his superiors, but the US government was unwilling to spend a penny on this project, and also determined that even if the project was successfully developed, the government had no obligation to purchase the product. Whether the Delta Force liked the product or not, they could abandon the project at any time. This result means that HK's research work must be completely self-financing, which is different from the XM8 program. The US Army paid for the development and purchase of the XM8 sample gun test, so even though the XM8 program has been canceled, HK itself has not suffered much loss. However, HK still decided to take over the M4 carbine improvement plan, so after signing a legal memorandum, the US government provided HK with the military carbines they needed for their research in order to carry out the project.

The improvement work started with observing the high-speed video of the carbine's action function. After carefully observing the weapon's firing cycle, a series of improvement projects were put on the work schedule. HK's engineers highly praised some design features of the AR-15/M16/M4 weapon system. From the beginning, they said that they would retain as many good features as possible of the weapon and only add some necessary improved features. However, there was a key component directly taken from the SA80 project that was adopted early because there was already a ready-made product. This was the new magazine improved by HK for the SA80.

HK was dissatisfied with the reliability of the M16 magazine, so when developing the G36, it used a completely new magazine that was not compatible with the NATO 4179 standard magazine. Although many companies have developed universal but reliable 4179 standard magazines, HK had to first consider the Bundeswehr's operating habits of using the G3 for many years because the G36 was originally developed for the German Wehrmacht. However, when improving the SA80, HK designed a new magazine to improve the reliability of feeding because the British Ministry of Defense required that the old and new magazines must be compatible. This new magazine still meets the NATO 4179 standard and looks very similar to the straight-bend-straight aluminum magazine of the M16, but it uses a steel full-curved magazine structure. Larry Weeks first introduced the new SA80 magazine to the United States in 2000 after visiting HK for the ill-fated HK-1911 project. He ordered 200 magazines for Delta Force to test and evaluate, which ultimately led to all units under the United States Special Operations Command (USSOCOM) deciding to use HK's steel magazines.

Interestingly, in 2007, the U.S. Army conducted a sandstorm environment comparison test on the M4, HK416, XM8 and FN SCAR. Although the M4's performance was far lower than the HK416, which ranked third, the test report pointed out that there was no need to replace the standard rifle, but recommended the use of new magazines. It can be seen that the magazine problem itself is one of the reasons for the high failure rate of the M16.

The outer shape of the bolt cam groove of the upper receiver of the Hk416 is cylindrical, while the traditional AR15 is square.

Although the HK416 steel magazine is relatively heavy, it is highly reliable. Therefore, the US Department of Defense ordered a large number of HK416 magazines to replace some of the M16 aluminum magazines.

HK416 steel magazine used by the US Navy Special Forces on the Mk18

The problem of feeding reliability was solved so easily, so the remaining gas system was the main target of HK. At the beginning, the main effort was to transplant the short-stroke gas piston system used in G36/XM8 to M4, which was the crux of a series of problems with M4. When the gunpowder gas enters the gas chamber through the gas hole, the piston moves backward under pressure. When the sealing rod at the front end of the piston is pulled out of the exhaust hole, the remaining gas is released from the exhaust hole in front, but the piston will continue to move under the action of inertia. After pushing the bolt assembly for a distance, the piston stops moving and returns under the action of the live rod spring, while the bolt frame drives the bolt assembly to continue recoil by inertia until the entire automatic cycle is completed. This new gas device is not only more reliable than the direct gas device of traditional AR-style weapons that is easy to be "dirty", but also greatly reduces the number of maintenance times for users. This also makes it only require a low level of maintenance during long-term field operations, especially suitable for special forces.

HK416 still uses many original parts of M4, such as bolt and extractor. But the improvement of gas system has extended the service life of these parts that are about to expire. Heat is the hidden killer that HK engineers found in the direct gas system of AR-style weapons. People who have been in contact with AR-style weapons know that the heat brought out from the gas tube enters the bolt frame, which not only makes the lubricant dry and volatilize quickly, but also forms carbon deposits and dirt in the bolt, which greatly reduces the service life of important parts in the action mechanism. After adopting the piston gas system, the action parts of the gun obviously "cool down" and greatly extend their service life. In the test, a HK416 fired more than 26,000 rounds. No part of the gun showed any type of damage due to such frequent use, and the barrel was very long-lived. This means that heat will not enter the action mechanism through the gas piston system. After firing multiple magazines in full-auto mode, you can directly touch the piston rod's recoil spring and the bolt handle with your bare hands (HK likes to disassemble the gun immediately after shooting in various videos promoting the HK416, allowing visitors to touch the bolt with their bare hands). According to Kyle Defoor, who retired from DEVGRU, the biggest benefit of switching to a gas piston is that it solves the "over gassed " problem after installing a silencer on a short AR (including the M4 and Mk18 CQBR ).

The original M16, after installing a silencer, will cause too much gunpowder gas to enter the bolt due to the change in the chamber pressure in the barrel. This will make the above reliability problems more serious. In addition, gunpowder gas will leak backwards from the bolt handle and hit the shooter's eyes (the problem of gas overflow can actually be solved by optimizing the internal design of the silencer. Some special forces purchased SureFire's SOCOM556-RC silencer and installed it on the Mk18 CQBR and were surprised to find that the feeling of gunpowder gas hitting their faces was gone) . Sometimes users have to replace the bolt handle with an enlarged size and airflow deflection device to prevent the leaking gunpowder gas from hitting them. This problem is most serious on the M4A1 with a shorter barrel, especially the CQBR. But units such as Delta and DEVGRU have almost used silencers in most of their operations in recent years, so they pay special attention to this advantage. Because the HK416 will never have this problem no matter what silencer is installed.

In addition, another improvement to the bolt is the addition of a firing pin safety. The AR-style bolt is designed to use a floating firing pin. Since there is no firing pin spring, the firing pin will move forward under the action of inertia when the bolt is closed, thereby hitting the primer of the bullet in the chamber. On the traditional M16, this force is not enough to fire the primer, and only a small pit will be knocked out. This is the same as most military rifles (such as AK, G36, etc.). The probability of accidental discharge when locked is quite low, unless inferior ammunition is used, such as bullets with protruding primers, or the primer is particularly soft. However, since the recoil speed of the HK416 bolt is much greater than that of the original M16, a recoil spring with stronger spring force must be used accordingly, which leads to an increase in the forward force of the HK416 bolt when it is recoiled. In order to avoid the possibility of accidental discharge when locked, HK company added a firing pin safety to the HK416 frame so that the firing pin will not hit the primer at the moment of locking.

One thing that must be made clear is that HK was not the first to use a gas piston device on an AR-style rifle. Before HK, the American RROC company had already launched an AR-style rifle that used an AR18 gas device, but it did not make a big impact in the market. Earlier, when Taiwan developed the T64 ( the prototype of the T65 rifle ) in 1975, it also transplanted the AR-18 gas device to the M16 rifle. This was because the propellant produced in Taiwan was much "dirtier" than that in the United States, and the combustion residue was large, and the failure rate was higher when it was directly used on the original M16 structure. However, this innovation of Taiwan did not attract the attention of other AR-style gun manufacturers. However, the T64 may only be the earliest design to transplant the AR-18 piston system to the AR-style rifle, but it is still not the earliest piston AR design, because the earlier piston AR was the 703 prototype gun developed by Colt in 1969 .

HK M4's technology is not original, there have been similar products with M16/M4 modified gas devices. In fact, Taiwan's T65 standard rifle is also a similar product with M16+AR18 gas device.

HK416 is a short-stroke piston AR rifle. Although it is not the first, it has set off a trend: Colt, LMT, KWRC, POF and other AR weapon manufacturers have each launched a series of AR products with short-stroke gas pistons. In addition, some companies have launched some "gas-blowing to piston" modification kits on the market. However, it should be noted that the design of modern firearms is a domino effect. For example, the 703 gas -piston M16 developed by Colt in the 1960s made many changes, even the size of the receiver. Since HK416, many other "gas-blowing to piston" solutions on the market have simply replaced the gas tube with a piston device. However, the original design of M16 did not consider the use of a piston device. If the piston is used to push the frame directly without making corresponding changes to the frame and the receiver, the unlocking force and the recoil spring tension will not be in the same line, generating torque on the frame. For example, when someone tried the PWS Mid-Length modification kit, the gas ring weld broke. Another person also had the piston rod bend and deform when trying the ARES modification kit, and broke a bolt handle. The HK416 has made many adjustments to the center of gravity, frame structure, and receiver, so it is both reliable and durable.

After completing the improvement of the gas system and related parts such as the bolt, HK engineers began to shift their attention to the rail system. They designed a four-way rail handguard system that can keep the barrel free floating so that various standard accessories and sighting systems can be installed. In addition, in order to make room for the gas device, the top of the HK416 handguard needs to be raised. In order to make the handguard and the rail height on the top of the receiver consistent, the top of the HK416 receiver is higher than that of an ordinary AR.

X-ray of HK416. The top of the receiver is raised to be flush with the upper rail of the handguard. The upper rail of the handguard is higher than that of traditional gas-blown AR to make room for the gas guide.

In order to provide long service life, HK also uses cold forged barrels, and uses high-quality European steel to manufacture barrels of 4 different lengths, including 10 inches, 14.5 inches, 16.5 inches and 20 inches. HK's promotional materials claim that the HK416 barrel has a quick-release function, but it is not really quick-release. It means that compared with traditional ARs, as long as the barrel is clamped in a vise, it can be disassembled. The barrel of a traditional AR does not have a flat surface for vise mounting, so special tools are required.

The AG36 under-hook grenade launcher originally developed for the G36 was also improved and named the AG416 Enhanced Grenade Launcher Module (EGLM, later finalized as the M32 GLM by the US military ). The AG416 EGLM can be quickly mounted under the handguard of the HK416 without any tools. At the same time, HK also modified the shape of the HK416 magazine well so that it can use the SA80A2 blank magazine. This blank magazine is also a product of HK's SA80A2 upgrade plan. There is a baffle at the front of the magazine so that only short blanks can be loaded into the magazine, so as to avoid the accident of loading the wrong live ammunition when blanks should be used for training. There is a yellow button in front of the magazine body. When the magazine is inserted into the SA80A2, the button will be pressed down by the front wall of the magazine well so that blanks can be loaded into the chamber. However, this design is often complained by some users, because although the HK416 magazine well can accept USGI magazines, it cannot use some magazines with a large front arc, such as PMAG. Moreover, these users will not buy SA80A2 blank magazines, so this safety feature is meaningless to them. Therefore, HK company modified the design of the magazine well on the latest HK416A5 , making it universal for all magazines that can be used for M16.

Both the original HKM4 and the later HK416 have been subjected to extensive live-fire testing in harsh environments, such as at the U.S. Army's Yuma Desert Proving Ground in Arizona, to test the effects of these improvements. In the best and worst gun conditions, all types of military and civilian ammunition were used, and all lengths of barrels with (or without) silencers were tested, and it was found that multiple parts of its action mechanism had significant improvements in reliability.

The finalized HK416 was also tested by the Delta Force. After one of the first batch of HK416 carbines with a 10-inch barrel successfully passed a 15,000-round durability test, the Delta Force placed a formal order for the first batch of hundreds of HK416 10-inch barrel weapon systems. So when will the HK416 be equipped to the troops? The earliest official public news was reported in the U.S. Army Times on March 1, 2007, which mentioned that the Delta Force planned to purchase a batch of HK416 upper receivers to modify the existing M4A1. The U.S. Federal Procurement Notice (No. FA5270-07-R0009) on March 28 showed that 84 sets of HK416 10-inch upper receiver kits had been purchased for the 1st Special Forces battalion of the Delta Force stationed in Ryukyu. However, according to Larry Weeks, the first batch of HK416s delivered had left the Oberndorf factory in July 2006 and were immediately put into combat use. The leader of the Delta Force gave a speech at the weapons factory ceremony, praising it as one of the most successful projects undertaken by the force and the buyer.

After the HK416 was equipped to the troops, the Delta Commandos found some defects that needed to be improved. One of them was that when the accessories were installed on the heavy handguard, the center of gravity of the entire gun would be very forward. While ensuring that the sustained firepower of the HK416 could be maintained to meet the requirements of a large number of fully automatic shooting in the specific tactical environment of USSOCOM, HK's engineers redesigned a lighter barrel, which successfully reduced the weight by about 7 ounces, alleviating the problem of the center of gravity being too forward - but it was not completely solved, and the top-heavy problem of the HK416 was still quite serious. Therefore, the SMU units under JSOC (commonly known as Tier 1, including the Army's Delta and the Navy's Special Operations Research Group, or DEVGRU) are basically not equipped with HK416 models above 14.5 inches, and most of them are even equipped with 10-inch models.

The reason why the HK416 is top-heavy is not only because the piston is heavier than a thin gas tube, but also because the ordinary model of the HK416 was directly installed with a thickened heavy barrel. Therefore, even the light barrel produced for the US special forces is thicker than the ordinary AR barrel.

The 10-inch barrel, the top one is a lightweight barrel designed for the US special forces order, and the two pictures below are the barrels of the ordinary HK416

The normal 14.5-inch barrel is a heavy barrel. The large round hole under the gas ring is used to install the HK GLM grenade launcher.

The M27 IAR's "heavy" barrel is actually the same outer diameter as a normal barrel, but with two less notches.

Of course, perhaps the old round plastic handguard can also solve this problem. Although many manufacturers produce replaceable AR-style handguards, the HK416 has changed the barrel installation interface, and the size of the piston device is higher than the original gas tube, so other AR handguards cannot be used on the HK416. For this reason, the SMU units found some other companies to help them design lightweight handguards that can be used for the HK416 (see [ HK416 lightweight handguard ]).

In addition, according to several interviews with HK managers on the HK German official website, there was a mention of a HK416A6 with a heavy barrel. If it really exists, then for the HK416 whose original "normal" barrel is a heavy barrel, this "heavy" barrel should be a more super-heavy structure. However, no pictures of the HK416A6 have been found so far.

HK is currently selling the complete HK416 on the market, and also provides upper receiver kits including barrels and bolts, which can convert existing weapons into HK416. Since the M16 receiver is designed to be unstressed, its service life is particularly long. The US military is very stingy when it comes to saving money. For example, the Mk18 CQBR equipped by the Navy Special Forces was originally equipped with the upper receiver provided by the factory to the existing M4A1 lower receiver. Later, the Navy purchased a large number of new "factory" complete guns and directly used the M16A1 lower receiver in stock. This can also explain why the Delta Commandos stationed in Ryukyu only purchased the upper receiver of the HK416. However, since the upper and lower receivers of the original guns are more closely matched, although it is possible to only replace the upper receiver components including the bolt, it is generally recommended to buy the whole gun. The biggest obstacle hindering the US military from purchasing HK416 is the origin issue. As a countermeasure, HK USA signed a contract with Wilcox Industries of the United States in 2007, with HK providing machines and technology to jointly produce HK416/417 and its semi-automatic civilian models MR223/308 sold in the North American market.

These are the appearances after only replacing the HK416 upper receiver

Combine POF's P416 lower receiver with HK416 upper receiver

HK416 upper receiver plus LMT lower receiver

These are photos of the HK416 upper receiver being replaced with the AR lower receiver.

It is said that the special forces SMU directly under JSOC (Joint Special Operations Command) prefers to choose HK416 as their first choice for new carbines, rather than FN SCAR, which is being promoted by USSOCOM and NSWC (Naval Special Warfare Center). This is the impact brought about by the Delta Force after purchasing the first batch of 500 HK416s. Many units such as DEVGRU, Green Berets, and Air Force PJ have begun to try out or equip HK416. Later, the DEVGRU members who participated in the "Spear of Poseidon" operation to assassinate Bin Laden used HK416 in the operation. Some rapid response units of the Army, such as the Asymmetric Warfare Group (AWG), also used HK416, but later the high-level Army was dissatisfied with this and asked to hand it over, which caused disputes. After the launch of the 7.62mm NATO caliber HK417, the HK416/417 gun family has become a strong competitor to the FN SCAR gun family. There is no detailed comparative test data on the superiority of these two series of weapons, but the aforementioned sand test conducted by the US Army in 2007 was not a comprehensive comparative test, but in addition to reliability, it also compared shooting accuracy. In the accuracy competition, the HK416 ranked first, with a slightly smaller dispersion than the SCAR and M4A1, and much better than the XM8.

Judging from the equipment situation in recent years (until 2013), the US special forces are equipped with more 5.56 HK416 and 7.62 SCAR Mk17, but not 7.62 HK417 and canceled 5.56 SCAR Mk16. It seems that although FN SCAR has better ergonomics, HK416 is exactly the same as traditional M16 in operation and does not require adaptive training. Therefore, it is the choice of frontline special forces to replace M4 series with HK416 with the same operation method and replace M14 series with Mk17 with better ergonomics. As for conventional forces, except for the Marine Corps equipped with M27 IAR , there is no chance to use HK416 (AWG has been handed in).

In 2011, HK launched the HK416 IC to participate in the US Army's "Individual Carbine" (the meaning of "Individual" is not "independent" literally, but "individual") bidding program , which intends to use a new carbine to replace the current M4 MWS. In addition to the HK416 IC, the sample guns participating in the IC program bidding include Remington ACR-IC , FN's FNAC , ADCOR's BEAR IC, Colt IC, LWRC's IC-A5, etc.

In 2012, HK launched the HK416A5 in Europe . The HK416 IC has some similarities with the HK416A5, such as the gas regulator has two positions, the standard position (N) and the silencer position (S); the double-sided rate of fire selector, and the left and right sides can be linked. But in more details, the HK416 IC is closer to the old HK416, and there are many differences with the HK416A5. In addition, because the weight requirements of the IC project are relatively strict, in order to reduce weight, the HK416 IC uses a thin-diameter "pencil tube" in the barrel in front of the gas hoop, while the barrel behind the gas hoop still maintains the outer diameter of the heavy barrel, but the barrel surface is grooved to reduce weight. Such barrel features are not available on other models of HK416 (because almost all HK416s are heavy barrels, even the light barrels specially developed for the delta are still considered heavy barrels compared to the pencil barrels of traditional ARs) . It is hard to say whether the design of the double-sided rate of fire selector and gas regulator was inherited by the HK416A5? Or it is because when HK416 IC was launched, HK company had already started to make these improvements.

In 2013, the US Army canceled the IC project, but the HK416A5 received an order from Europe.

HK416 IC

The shape of the gas regulator is similar to the later HK416A5

Through the heat sink, you can barely see the grooves on the surface of the barrel.

The transparent plastic magazine of HK416 IC was later packaged with HK416A5 and finalized as G38 and sold to the German government

The military units that have been confirmed to be equipped or using HK416 include: the Special Forces KCU of the Netherlands Army (also equipped with HK417), the Turkish Army, the Italian Navy Special Forces, the Polish GROM, the Malaysian VAT69, the Indonesian Marine Corps' Counter-Terrorism Force Detasemen Jala Mengkara, and the Albanian BOS. In addition, the US Capitol Police Special Forces CERT, the Department of Homeland Security, the Idaho Drug Enforcement Administration's SRT, the Department of Justice, the Maine SWAT, the Nashville SWAT, the NASA SWAT, the Fairfax SWAT in Virginia, and the Trussville Police Department in Alabama are also equipped with HK416, while the Lake Wales Police Department in Florida is equipped with both HK416 and HK417.

The above-mentioned troops do not have many equipments because these units have few people. However, HK successfully won a contract worth 16.6 million US dollars in 2007 to provide 8,200 HK416s and related accessories and spare parts for the Norwegian army. In order to replace the original G3 rifles, the Norwegian army went through a rigorous new rifle selection test. Originally, only HK's G36KV3, Canada's Dimaco's C8IUR and Swiss Light Arms' SG551-SB could enter the final test stage, but unexpectedly, HK416 suddenly emerged and won the bid. However, the HK416 purchased by the Norwegian military is slightly different from the US military. This is an improvement made at the request of the Norwegian military. The main improvement is to modify the firing pin stop pin to prevent the firing pin from being lost during disassembly and maintenance. There is a unique gas regulator, and the hammer can be adjusted to the safety in any case (ready to fire or already fired). Considering that Norway will install a laser sight on the top rail, the aiming baseline seems to have been moved up.

The Norwegian HK416A3 is slightly different from the HK416A2 in most countries.

The Norwegian HK416 is named HK416A3. In fact, the HK416 equipped by Delta Force, SEAL Team 6 and other units before this was HK416A2, which was also the model widely purchased by many users before the launch of HK416A5. In addition, HK company will use different suffixes on the receiver inscription to indicate the country name, so the Norwegian model is called HK416N, the later French model is called HK416F, and the HK416D purchased by the US special forces actually refers to the original German model (except for the US Marine Corps' M27 IAR). The performance parameters of HK416D are as follows:

The development process of each series of HK416 is as follows:

The HK416 is a basic model, without a firing pin spring and firing pin safety;

The HK416A1 has a firing pin spring and firing pin safety, and only the left side of the receiver has a groove to accommodate the bolt handle limit hook;

HK416A2 has Over The Beach capability, which means that the gun can fire immediately after it is out of the water. HK has even made a promotional video for this.

HK416A3 is the Norwegian model;

The HK416A4 was changed to a two-stage trigger;

The HK416A5 was the first model to have major improvements;

The HK416A6 is said to be a heavy barrel version of the HK416A5;

The HK416A7 is the second model with major improvements.

Turkey copied the HK416A2 in 2008 and named it Mehmetçik-1 . Later, it developed the 7.62x51mm caliber MPT-76 based on it 

10-inch upper receiver conversion kit

HK M4 undergoing reliability testing at the Yuma Proving Ground . One of the guns in the picture uses the upper receiver of the M16A2 instead of the HK-produced upper receiver.

HKM4 booth at the 2004 Las Vegas Gun Show

Model with 14.5- inch barrel

HK M4 during live-fire demonstration at the North Las Vegas Police Department shooting range during the gun show

16.5 - inch heavy barrel model

10- inch barrel model

The final HK416

HK416 piston system

HK416 14.5-inch carbine version

16-inch type

20-inch type

14.5-inch model with AG416 attached

HK416 10-inch CQB model and AG416 (AG36 changes its name for each gun model)

New stock introduced in 2008

                                          

New buttstock with storage space

10-inch model with new stock

14.5-inch model with new stock

16-inch model with new stock

20-inch model with new stock

Several HK416 models exhibited at SHOT SHOW 2006

The early HK416 ejection port dust cover was made of metal (left), but was later changed to plastic (right)

HK416/417 photographed by SMG Lee at SHOT Show 2007

HK416 exhibited at SHOT Show 2008 AAC's new flash hider and matching quick-release silencer on display at the SHOT Show 2008 HK416D exhibited by HK at the 2008 Association of the United States Army Annual Meeting, photographed by SMG Lee Visitors to the HK factory in Oberndorf test-fire the HK416 HK416 at the 2008 Paris Defense Exhibition ( provided by war correspondents ) HK416 at the HK Media Open Day in August 2011. The grenade launcher is not HK, but LMT's M203 style. Photos posted by some individual users on the HKPRO forum This is a civilian user who bought a HK416 upper receiver, combined it with an ordinary AR lower receiver, and engraved the HK inscription himself. A close-up photo posted by a user named Gewehr 416 on the HKPRO forum The barrel and gas guide device, this one is an ordinary heavy barrel Piston and piston rod details The hole through which the piston rod enters the receiver Bolt Group frame Bolt buffer Firing pin Photos of Norway announcing the upcoming adoption of the HK416 Turkish Defense Minister holding MKEK1 Türkiye's copy of HK416 MEHMETCİK-1 (or MKEK1) The Norwegian HK416 receiver is engraved with "HK416 N" Photos of the Norwegian selection: HK416 and its competitors HK416 using Simunition FX Marker Bullet

HK416 light handguard

As mentioned earlier, due to the heavy handguard of HK416 and the weight of the gas piston system itself, the center of gravity of HK416 is much more forward than that of traditional AR, which has been criticized by some special forces who are used to using AR. In addition, since the surface of the handguard is covered with Picatinny rails, you may need to wear gloves or install guards on the rails to improve the feel when operating. On the other hand, in recent years, a new trend has emerged in AR rail handguards - in the past, people wanted the entire handguard to be made of rails, but now only the rails are retained on the top of the handguard, and only screw holes for installing Picatinny rails are reserved at 3, 6, and 9 o'clock, and a small section of the rail is installed when needed. This can not only reduce weight, but also improve the feel. However, although there are many AR handguards on the market for users to choose from, none of them can be directly installed on the HK416. Although the barrel installation method of HK416 is the same as that of traditional AR, which is fixed by barrel screw, the thread extending from the front end of the receiver is longer than that of traditional AR. The purpose is to install HK416's own rail handguard. In fact, HK company deliberately designed some differences on HK416 from standard AR. Some designs are not for the reliability of changing to piston type, but to prevent users from purchasing other parts at will to assemble the gun.

HK416 barrel connection method The picture shows the barrel screw thread at the front end of the HK416 receiver. The length of this section is longer than the AR standard. The barrel screw sleeve of HK416 also has the function of fixing the handguard. The annular groove marked 2 in the upper figure is the bayonet for the handguard fixing bolt. The 3 and 4 marked in the lower two figures are the handguard bolts. The bolts can be loosened and the handguard can be removed by using the bolt as a wrench. Therefore, it is very easy to replace the handguard of HK416.

In short, if the special forces want to improve the center of gravity or feel, they must redesign a new handguard specifically for the HK416. To this end, SOCOM found Geissele Automatic, a well-known company for making match-level AR trigger groups ( both Mk12 and M110 use their triggers), and asked them to design a handguard that can be used for the HK416 (but there are also claims that the Delta Force directly asked Geissele for the request). In 2012, Geissele launched the SMR handguard for the HK416. This aluminum alloy handguard only retains the Picatinny rail at the 12 o'clock position, and only the screw holes for installing the Picatinny rail are reserved at the 3, 6, and 9 o'clock positions. A small section of the rail is installed when needed. Since a large section of the rail is removed and the length is slightly longer than the original, the appearance seems to be a little "slim". The barrel mount of the Geissele SMR Mk1 is made of special alloy steel and is about 2 inches long, which allows the SMR handguard to withstand about 1,000 pounds of pressure. But later Geissele found that this was unnecessary, so the barrel mounts of later models were changed to aluminum alloy. As for the long heat dissipation holes on the handguard, they have no additional function. Although Geissele later produced light handguards for ordinary ARs with heat dissipation holes compatible with accessory interface functions, such as the KeyMod interface on the Mk4 model and the Mk8 model using Magpul's M-LOK interface (in fact, Geissele also participated in the formulation of the M-LOK standard), the SMR handguard for HK416 has not been modified in this regard. Although the appearance makes people feel that the Geissele SMR is lighter than the original HK416 handguard, it is actually the same weight. Taking the 10.5-inch model as an example, the SMR handguard and the original HK416 handguard both weigh 12.6 ounces (about 357 grams). If the SMR is equipped with 3 sections of rails, it will be slightly heavier (414 grams).

Geissele Automatic's SMR handguard, the picture shows the 10.5-inch SMR

Comparison between HK original handguard and Geissele SMR handguard. It seems that SMR is a bit more "slender".

Taking the 10.5-inch model as an example, the Geissele SMR handguard is as heavy as the HK416 original handguard, and the SMR is slightly heavier after adding the rail.

Multiple versions of SMR in different periods

14.5-inch Geissele SMR handguard

Delta Force using SMR handguard

A Delta Sniper using an HK416 with an SMR handguard during a sniper match

Delta Force member Savard Ryan using the SMR handguard

HK416 RECCE rifle with SMR handguard

Remington's RAHG lightweight handguard for DEVGRU

HK416 with RAHG handguard installed, this should be DEVGRU

RAHG handguards of different lengths

Ding Ding's photography practice in 2015, a collection that domestic AR fans envy and hate. His HK416 was replaced with a RAHG handguard

This is the DDL handguard HK416 that SMGLee saw in the SEAL's gun arsenal

Some people say that this is a HK416 equipped with a DDL handguard by DEVGRU, but the DBAL laser pointer and Inforce tactical light installed on the gun are probably modified by civilian players themselves.

The HK416/MR223 lightweight handguard launched by MIDWEST has a heat dissipation hole on the surface that is also an M-LOK interface.

DDL's HK416 light handguard

On the other hand, Remington was also commissioned by the Navy DEVGRU, which is also a SMU, to design the same type of HK416 handguard RAHG (abbreviation of Remington Accessory Handguard). Remington RAHG also only retains the top Picatinny rail, and only reserves screw holes for installing the Picatinny rail at 3, 6, and 9 o'clock. The long heat dissipation holes on the handguard look like Magpul's M-LOK interface, but in fact they are just holes for pure heat dissipation and weight reduction.

Later, other companies also provided similar products, such as MIDWEST's MI HK416/MR556 handguard. However, the most popular HK416 or MR223 light handguards on the market are SMR and RAHG, which are said to be specially produced for SMU. In fact, in 2012, DDL (the main contractor of SOPMOD II ) also produced a small batch of round light handguards for DEVGRU, but there were no new orders after that. It is estimated that the troops did not like it after trying it. DDL handguards were also sold publicly on the market for a short period of time, but unfortunately there was a lack of orders from special forces, which is an important publicity gimmick in the civilian market, so very few people bought it, so DDL simply stopped production. It is difficult to find this type of product on the market now. Basically, the two main forces in SMU have different main light handguards. DEVGRU focuses on RAHG, while Delta focuses on SMR. Therefore, in most cases, you can judge which unit's SMU it is by looking at the handguard (but not absolutely).