Heckler & Koch M27 - First Impressions
By Miles Vining

Note:All dimensions, acronyms and official terms are from Marine Corps terminology and refrences.

There is no telling what small arms are doomed to shelf space and others to be revolutionary on the battlefield or home front. The M27 from Heckler and Koch and its civilian version, the MR556, are current examples from which their impact is still being measured. With the M27’s current employment with the United States Marine Corps and deployments to Afghanistan, only time will tell if this new weapon will be a game changer or not.


Finding the perfect balance between firepower, weight, reliability and ammunition capacity has constantly been a challenge for Light Machine Gun (LMG) development. These support weapons for the traditional infantry squad have usually been a compromise among these four factors. The BAR lacked the magazine capacity to be truly successful, while the M60 gained the infamous nickname of the “Pig” due to its excessive weight and bulk. The M249 Squad Automatic Weapon (SAW) came very close to being the exemplary LMG but quickly lost its glory through its high malfunction rate and weight. Recently, the United States Marine Corps decided upon a solution that takes the Squad Automatic Weapon to whole new level.

Several years ago, while observing a Marine unit conducting pre-deployment training on Range 410 Alpha in Enhanced Mojave Viper, Twentynine Palms, California, a high-ranking officer watched a squad clear a trench as part of the training exercise. The squad’s SAW gunners established a support-by-fire position while the squad rushed into the trench and continued on with the range. After it was over, the officer asked the battalion Gunner (Chief Warrant Officer - an expert on Infantry small arms and tactics) why the SAWs couldn’t come into the trench with the main effort. The answer given was that the SAWs would slow the squad down and could not be effective in the trench because of the gun’s weight and open bolt operation. Finding this tactic detrimental to the way Marines fight today, the officer and battalion gunner decided to act. Requests were made to the firearms manufacturing community and a competition for a new squad LMG ensued.

The competition was designated the “Infantry Automatic Rifle” and the Marine Corps made it very clear that it had to fill the place of the SAW but also be a lighter and more portable weapon. Changing the designation from SAW to IAR showed that the Marine Corps was dedicated in finding a mobile automatic platform instead of being burdened down with the old technology. It had to weigh less than 12.5 pounds and accept the US standard 30 round magazines. It had to fulfill the function of the SAW but also be lighter and more mobile. Six commercial companies accepted the challenge, and three made it down to final testing: FN Herstal, Heckler & Koch (H&K), and Colt. FN’s contender was a modified SCAR; H&K’s and Colt’s weapons were both modified versions of their respective entries into the Black Rifle market. All except H&Ks were open bolt. After months of exhaustive testing, H&K came out on top. Trumping its competitors in areas of precision, reliability and malfunctions, the H&K submission produced outstanding results. Accuracy was unparalleled compared to the other two. In fact, it is reputed to be the second most accurate weapon in the Marine Corps inventory after the M40A5 sniper rifle. Designated as the M27, H&K had proven itself once again.

In 2010, Marine Corps Systems Command bought an LRIP (Low Rate Initial Production) quantity of M27s slated to replace or complement M249 SAWs in four Infantry Battalions and one Light Armored Reconnaissance Battalion (LAR). All units had the opportunity to train and deploy with the M27 throughout 2011 and into 2012 in the War on Terror. The M27 is operating so well in combat that the Marine Corps has already ordered the full contract quantity. The current recommendation is to replace all the former SAWs with M27s throughout the rifle platoons but current individual assignments are at the discretion of the company commanders.


Due to the M27s commonality with the M16/M4 rifles, user operation is similar. Instead of direct impingement, it is gas piston operated. It has a free floating barrel, and uses a more efficient bolt than an M16A4. These are the only major functional differences to the standard issue M16A4 that all Marines are familiar with. Cleaning the weapon is made much easier by the gas piston that keeps a good portion of the carbon out of the bolt carrier and upper receiver. Also, unlike the M16A4, the M27 is highly ambidextrous. Sling mounts, fire selector, and charging handle can all be made left or right handed with little modification. Point target range is 550 meters while area targets are 700 meters and maximum range is 3,938 yards. The Fleet Marine Force (FMF) chose the 16.5” barrel.

The butt stock is similar to the M4 four position collapsible stock except that it is less sluggish and is six position. Unlike an M4 stock, it is easily removed by depressing the position toggle. It has one circular and two lengthwise sling keepers mounted at the rear allowing a diversity of slings to be used. The butt pad is rubber. Fully extended, the M27 is 37 inches (M16A4 length: 39.63 inches) and with the stock collapsed it is 33.66 inches (M4 collapsed length: 30 inches).

The M27 has a three position fire selector; Safe, Fire, and Auto, with the traditional H&K pictograms for each. Controls are on both sides of the receiver. The pistol grip is very comfortable and has a polymer pebbled surface to enhance grip. There is a battery compartment in the pistol grip that is held in place by a pivoting slider and the grip itself is more ergonomically designed than the standard M16A4 pistol grip. The magazine well has a flared opening that aids in magazine insertion but prevents Magpul PMAGs from being fully inserted. This leaves room for further magazine improvement if any manufacturer is up to the challenge. The weapon serial number is stamped upon both the upper and lower receivers right above the magazine release catch and left side safety in traditional European fashion. All M27 serial numbers begin in “USMC” and H&K proof marks are to the left of the serial number on the upper receiver.

The upper receiver has a 12 o’clock rail that is interconnected with the Free Floating Rail System (FFRS) by a U-shaped lug. A captive locking screw adjacent to the magazine well additionally secures the FFRS. To take the FFRS off, grasp the bolt carrier with the thumb or index finger on the extractor in order to turn the strongest lug into a screwdriver. An important reason for a finger being on the extractor in such a position is that only the strongest lug is engaged and not the weak ones opposite the extractor. After only a quarter turn, the bolt carrier is unnecessary; hand strength is sufficient enough to complete disassembly. Only the 12 o’clock rail is marked with reference numbers up to 42 while the 3, 6, and 9 o’clock rails are left blank. Unfortunately, few attachments can be mounted directly underneath the handguard screw due to its proximity to the 6 o’clock rail.

The M27 also comes with H&K rail protectors that take up most of the rail when mounted. They are secured at the end of the protector with a plastic indent. These too have a polymer pebble surface and provide good grip. There is no permanent sling mount but all M27s come issued with a rail mounted sling mount that uses a single screw to secure it in between rails. The ejection port cover is polymer. The charging handle has an extended release lever and pins so that it can switch to the other side. Right above the chamber on the left hand side of the barrel, it reads “HK 5.56mm” alongside an H&K proof mark. The bird cage flash hider can mount all attachments that an M16A4 can such as Blank Firing Adaptors (BFAs), muzzle caps and Bayonets (bayonet stud is included for the USMC OKC3S bayonet).

The bolt carrier and gas piston system are the true “moneymakers” of the M27. Their design is what makes the gun run so well and so reliably. The bolt carrier is similar enough to an M16A4 for it to lock into one and chamber a round. Whether or not the hybrid weapon will function reliably is unclear. On the flip side, a M16A4 bolt carrier cannot fit in an M27. The firing pin retaining pin is captive while the firing pin has a spring that keeps the bolt forward. This spring prevents accidental discharges should the weapon be dropped.

The gas piston system consists of the piston rod, piston and gas block. The piston rod has a captive spring and its lateral movement is no more than an inch at the most. The piston is the dirtiest part of the weapon after firing and is simple to clean. It fits into the gas block, which has a vent port facing downrange on top of the barrel. The gas vent is larger in diameter than the HK416 but this change in design made a significant improvement in reliability and is expected to save the Marine Corps in excess of several hundred thousand dollars.

The M27 comes with three sighting systems; Back Up Iron Sights (BUIS), Squad Day Optic (SDO), and the Ruggedized Miniature Reflex (RMR). The Sight Unit, SU-258/PVQ Squad Day Optic was created for the M249 SAW with a contract from Trijicon in 2009 but has been since mounted on the M27. It is a 3.5x35 machine gun optic that is mounted to the rail via LaRue Tactical throw mount with duel locking lugs. It has Tactical Tough flip up dust covers and comes with an Anti-Reflection Device (ARD, known as a honey comb for its pattern) screwed onto the objective lens. The reticle is an illuminated horse shoe around a center dot with a small post below. For distances of 100 and 200 meters the aiming markers are the top and bottom tips of the dot respectfully. For 300 meters it is the tip of the illuminated post and further ranges are marked on down the mil scale below the tip. The crosshair mil scale goes out to 35 mils on the horizontal lines and 40 mils on the vertical lines. On the vertical range scale there are range estimation stadia lines (Bullet Drop Compensator) that can provide accurate range estimation based on the shoulders of an average sized man (19 inches). It also has brackets for vehicle estimation both side and frontal views by using the tires.

On top of the SDO is the RMR, a small reflex sight intended for engagements under 100 meters. Unlike the M240B MDO (Machine Gun Day Optic) RMR, which is rail mounted to the optic, the RMR is screwed in and cannot come off except with the use of tools. An important aspect of the RMR is that the dot is rather large in the holographic image and proper cheek wield cannot be maintained while acquiring a sight picture. A gunner must take careful measures to secure a proper zero and maintain it with good muscle memory. The RMR uses adjustment dials that require a flat blade and don’t have a dust cap. The SDO has turn knob adjustment dials with dust caps.


On live fire ranges the M27 has preformed flawlessly with sub- Minute of Angle groups typical. Transitioning from semi to auto is simple and very effective when switching from long range targets to quick bursts on close engagements. On a recent live fire training evolution, the unit’s M27s went through more than 300 rounds per gun in the span of an average of 20 minutes in completing an evolution. The author only experienced one jam, caused by a double feed while simultaneously gripping the magazine well and magazine.

The gun is extremely controllable on fully automatic provided a proper stance and proper technique is used. M27 gunners were engaging targets well out to 500, 600 meters with one shot hits and immediately taking out near targets of opportunity with bursts and magazine dumps. For Military Operations in Urban Terrain (MOUT), the M27 performed at the same level as an M4, if only a little longer and heavier (7.9 lbs unloaded). The RMR holographic sight was perfect for live fire kill house evolutions where Marines couldn’t afford to be tunneled into the SDO while in a MOUT environment.

But the M27 is not without drawbacks. Since the magazine capacity can barely match the rate of fire, gunners would routinely empty entire magazines in seconds only to reload and repeat. Marines were running through evolutions with an excess of sixteen magazines in pockets, pouches and whatever else was improvised. Many more magazines were split up among the squad to carry extra. In comparison, standard load for a rifleman is seven magazines and M27 gunners were carrying nearly three times that amount (21 non-tilt follower magazines). Magazine couplers helped with reloads but they take up space on flak jackets and in pouches. PMAGs will not work because of the frontal plastic bevel, which prevents full insertion into the magazine well. The bevel can be filed down to work but, this is highly questionable and against regulation. Questions have been raised on the use of drums designed for the M16A4. These may not work reliably in military operations overseas. They also cannot stand up to extreme temperatures that military equipment operates in. Surefire has just come out with 60 and 100 round magazines that work reliably in the M16A4, but not in the M27. Currently, Surefire is working to redesign the new magazines in order to work in the M27 as of March 2011.

Grippods were an issue as well. Some gunners had theirs broken within the opening minutes of evolutions. These fore-grip combinations are not designed to be used with machine guns, which need a rugged platform to anchor them to the deck. The Grippod does not provide enough elevation for a gunner to successfully engage targets at an incline. The Marine Corps has replaced the Grippod with the LaRue design bipod system. Also, it is worth noting that occasionally the screws on the LaRue throw lever mounts would come loose after an extended period of sustained firing.

The M27 barrel is not meant to be readily replaced if there is a hot barrel. Tests have shown that the sustained rate of fire is 36 rounds per minute (rpm) at 120 degrees Farenheit for a 600 round load. The cyclic rate of fire is 750-800 rpm (M249 SAW 850 rpm). Little guidance has been provided in the event of a hot barrel except for the shooter to be careful and conserve rounds. During the early testing of the M27 there was a torture test of the gun’s reliability that was called the “Wells Test” named after the Captain who implemented it. It took 1 minute and 36 seconds to fire through 22 fully loaded magazines all lined up next each other without a single malfunction. Yellow M4 BFAs are standard.

As in all weapons in the field, small parts begin coming off after extended use of the weapon both in evolutions and everyday use. Battery compartment covers, optic dust covers and ARDs have all been seen to come apart and off if not constantly checked. Most units have it as Standard Operating Procedure to secure serialized gear to the weapons with zip ties and 550 cord. Gunners must be wary of placement with such extremities because if positioned in certain areas they melt if in contact with the barrel (PEQ16) or interfere with disassembly of the weapon (SDO to FFRS).


The Heckler & Koch M27 has made a significant impact on the way Marine squads conduct operations. The M16A4 familiarity makes it perfect to issue to Marines already so ingrained with that weapon. Its reliability and weight take away the M249 SAWs principal drawbacks. Some have even speculated that this weapon is an indirect path that the Marine Corps is taking to get more reliable squad level small arms into the hands of Marines without going through the headache of replacing the M16A4. Such programs and rifles have faced opposition ever since their inception (SPIW 1960, ACR 1986, OICW 1990, XM8 2002, SCAR 2007). Overall, this is a very fine weapon and has definitely exceeded expectations. The grunts love it, and that is the most enduring compliment any firearm or piece of gear could earn.

(Special thanks to David Dimaruo, Tom Durwood, Edward Young and the Marines and Corpsmen of 3rd Platoon, Charlie Company, 1st Battalion, 9th Marines.)

This article first appeared in Small Arms Review V16N2 (June 2012)
and was posted online on April 20, 2012


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