By Christopher R. Bartocci

Last month we looked at Type’s A and B of Colt’s SCAR (Special operations forces Combat Assault Rifle) program. Both used the traditional gas impingement system as found in the M16/M4 family of weapons and fared very well in the trials. However, there was an unwritten requirement that SOCOM wanted a conventional piston operated weapon. They felt it would be more clean and reliable under the extreme circumstances that they operated under.

Colt set out to develop their own piston driven mechanism. Piston systems were nothing new to Colt as they had experimented with it many years ago. In the late 1960s to early 1970s, experimentation was going on at Colt, Rock Island and Winchester to develop a standard piston mechanism to deal with the problems the early rifles had with the switch-over to ball powder. This also was as a response to the publicity of the reliability of the AK47. In the end, a report in 1968 stated that the 10 prototype weapons performed about equal to the current M16A1 rifles. Colt developed the model 703 as a piston driven operating system. Although totally unlike the current SCAR design, it indicates that Colt had investigated this in the past. The 703 was a full-length rifle with a piston rod that was attached to the bolt carrier, much like the AK-type piston. By the time Colt had concluded the development of the 703, all the changes made to the M16A1 and ammunition made a piston-operated mechanism unnecessary.

The Colt 703 rifle when fired, the bullet would propel down the barrel, and gas was bled from the barrel into the gas cylinder created between the end of the piston rod and the front sight base. The piston rod, being attached to the bolt carrier group, would move rearward extracting and ejecting the fired cartridge case. When the bolt carrier group reaches it’s furthest rearward motion the buffer/buffer spring would drive the bolt carrier group forward stripping a round from the magazine, chambering it, and the bolt would lock into battery ready for the next shot.

Colt SCAR Type C

SOCOM’s unwritten requirement for a piston operated rifle was based upon their belief that this system kept the gun cleaner due to hot gasses not being blown into the bolt carrier causing fouling. This is especially true when being fired with a suppressor.

Colt began work to design their own piston system. With the requirement for a free-floated barrel, Colt opted to use their newly designed one-piece upper receiver. Keeping the legacy M4 platform was important as it was very user friendly. Once the shooter grasps the pistol grip, all manipulations of the selector and magazine catch can be made without manipulation of the shooters hand. The left hand will insert the loaded magazine a hit the bolt catch to reload. Due to the magazine dropping free and the bolt holding open on the last shot, reloading can be accomplished is seconds. An added benefit to keeping this platform was taking advantage of the existing familiarity of the operators’ use with the M4A1 carbine.

The SCAR Type C Upper Receiver

The upper receiver chosen was the Colt proprietary one-piece upper receiver. This allowed the barrel to be mounted to the receiver and permitted to free float; increasing accuracy as well as assist in cooling. The upper receiver utilizes a forward assist assembly, fired cartridge case deflector and an ejection port dust cover. There is a continuous Mil-Std 1913 rail that goes from the top of the charging handle area to the front sight base. This will allow the mounting of multiple optics including night vision, reflex sight as well as a laser. The side rails allow the operator to mount flashlights or other accessories. The bottom portion of the rail is removable allowing the mounting of a grenade launcher. When the standard cover with the rail is on, a vertical pistol grip may be installed. During testing, the newly designed Grip Pod Systems vertical pistol grip was used. This vertical pistol grip/bipod is made of 7075 T6 aircraft aluminum, the same as the Colt SCAR receivers. The bottom of the grip turns into a spring-loaded bipod with a push of a button. When the operator drops to the prone position and engages the bipod, the carbine has a stable base for aimed firing. When the bipod is engaged and the weapon shouldered, the magazine will not snag on the ground.

The carbine utilizes the same BUIS (Back Up Iron Sight) as the Colt Type A. The rear sight is a modified Colt carrying handle rear sight. Colt took a standard carrying handle and removed the handle just leaving a lightweight rear sight. There are no sharp edges to snag. It is adjustable for elevation out to 600 meters and has two sight apertures. A 0 to 200-meter close and a long-range aperture. However, any BUIS can be used whether it be an ARMS #40 L or a Knight Armament BUIS.

The front sight is a Colt designed foldable front sight assembly attached to the gas block. This same front sight assembly was used on all three of Colt’s entries and was activated and locked by a button on the left side. This utilized a square 4-notch front sight post and is adjustable for elevation only.

The Colt Piston Operating System

The piston system is very simple and very reliable. In firearms design there are two basic piston systems. The first is where the piston/operating rod is directly attached to the bolt carrier such as the AK47/AKM. The second is the short-stroke tappet where the operating rod strikes the face of the bolt carrier driving the carrier rearward while the piston rod reciprocates back to its rested position in front of the firearm such as the AR18, SKS and FN FAL.

The system chosen by Colt is the latter. By going with the two-piece operating rod the weight may be decreased. Colt has been working on their piston systems for a couple of years in their model shop. In 2003, a prototype was made showing an early attempt of their system. Over the next couple years their design would be modified and perfected to the final system they chose for their SCAR candidate

The final system begins with their proprietary one-piece upper receiver. The barrel is secured to the inside of the receiver and the barrel left free-floating. The system consists of the op rod and return spring. The front of the system consists of the gas cylinder and the mechanism is locked into the weapon by a large pin in the front sight/gas block. There is a gas relief vent in front of the gas cylinder that vents through the front of the front sight assembly. Colt has tested this operating mechanism with over 18,000 rounds without cleaning and without failure. This piston system does not require routine maintenance during cleaning.

As the bullet travels down the barrel upon firing, the bullet passes the gas port and gas is directed into the gas expansion chamber, driving the piston rearward. The rear of the piston impacts a modified carrier key on the bolt carrier group driving the carrier group rearward. While the carrier group continues rearward, the piston rod returns to its forward resting position. On the bolt carrier group’s rearward travel the bolt unlocks, extracting and ejecting the fired cartridge case from the carbine. Then the compressed heavy buffer and spring return the carrier group forward stripping an unfired cartridge from the magazine, feeding it into the chamber, and then the bolt locks into the barrel extension. The carbine is ready for the next shot to be fired. Another benefit of the piston-operated system is the ability to set the cyclic rate of the weapon. Colt chose to make the SCAR Type C fire at 800 rounds per minute comparable to that of the M4A1 with Mk 262 Mod 1 ammunition.

The Bolt Carrier

The bolt carrier group looks very similar to the standard M16/M4 family of firearms but with one major change: a new bolt carrier key. Also, there are no gas rings on the bolt due to the expansion chamber being in the front sight assembly instead of the back of the bolt carrier group. Another innovation that Colt has done is to change the finish of the bolt and carrier. It has a proprietary UCT Defense UltraChem (nickel boron) finish to eliminate the need for any lubricant whatsoever. This slippery finish needs merely a wipe with a rag to clean. This coating also improves corrosion resistance. The extractor utilizes the improved gold extractor spring with the stronger black extractor buffer.

The Barrel

As per specifications, the barrels come in two different lengths. The standard carbine barrel length is 14.5 inches and the CQC (Close Quarter Combat) barrel is 10.5 inches. Both barrels are heavy barrels to insure they can take the required heavy firing schedule demanded by SOCOM. The barrel utilizes the standard 1 turn in 7 inch rifling twist that is required to stabilize the Mk 262 Mod 1 ammunition currently in use by SOCOM. Additionally, as per requirements, a Knight’s Armament Quick Detach flash suppressor is installed for use with the silencer. The front sight base has a bayonet lug for mounting a bayonet on both barrels even though one cannot be mounted on the 10.5 inch barrel.

The chamber has been modified to comply with the “Over the Beach” requirement specified for the SEALS.

The Lower Receiver

The lower receiver is identical to the ones used on Type A and B. It is a standard M4A1 lower receiver with the modified selector lever. As per requirement, this ambidextrous selector operates over 90 degrees of travel (as opposed to the Colt standard of 180 degrees). After testing was completed, this change was not well received. The reasoning in unclear as to whether they were just too used to the standard or if it did not manipulate as fast as the original.

The magazine release is the patented Norgon ambidextrous version. The stock is the VLTOR stock with dual battery compartments for the optics. This is a standard four-position Colt buffer extension with a H2 buffer. Due to the carbine utilizing a heavy barrel, the buffer with 2 tungsten weights and 1 steel weight was necessary to prevent light strikes from bolt carrier bounce. Improved hammer/trigger pins are used that are manufactured of stainless steel. This increases service life especially with heavy volume of fire required of the SCAR weapon. The finish is done in the required flat earth finish (coyote brown) done by Kal-Guard.

Conclusions

The opportunity arose to test fire Colt’s Type C SCAR in their engineering range in the basement of the factory. There was little difference in the feel between the direct gas and the piston driven carbines and their cyclic rate was about the same. The carbine fired was quite worn and neglected from the SCAR trials. However, the carbine functioned flawlessly; firing nearly 500 rounds in 15 minutes. The bolt carrier group was completely dry without lubricant.

There seems to be little doubt that the next generations of M16/M4 carbines will be piston driven mechanisms. Colt plans to introduce a piston driven law enforcement carbine in early 2006.

With the SCAR program moving forward with procurement from FN Mfg. Inc., only time will tell how the new weapons will stack up compared to the M4A1 carbines currently in use. The SCAR trials were without a doubt the most grueling small arms testing in the world since the original Armalite AR-15 was pitted against the government designed M14. Lessons learned in this weapons development program will influence further research and development of further upgrades or new weapons designs of the future.

Since the introduction of the Colt Commando and XM177-series carbines, the U.S. military has had a need for a compact version of the M16, the longest serving small arm in U.S. history. Even though never officially adopted, these carbines saw extensive use in every theater of operations the U.S. and her allies were in.

In 1985, U.S. Government contract DAAA21-85-C-0192 was awarded to Colt for the development of the XM4 carbine, the first general-purpose carbine since World War 2. The contract had very specific wording in regards to parts commonality with the newly adopted M16A2 rifle. Particular effort was made to keep as high of a number of parts compatible with the M16A2 as possible. As first envisioned, the XM4 was to be used for troops who could not carry a rifle but needed more firepower than a handgun. It was to fill the same role as that of the M1 Carbine.

Parts Commonality as Defined by DAAA21-85-C-0192

Specifically stated in the requirements was that the carbine would utilize the newly adopted M855 ball cartridge as well as be functional with existing M193 ball ammunition. The barrel will have the same 1 turn in 7 inch rifling twist as the M16A2 and be 14.5 inches in length. The barrel must be made to accept the current MILES shooting simulation equipment as well as utilize the M16A2 compensator. The carbine must have the 3-round burst limiter of the M16A2. The polymer furniture must be made of the same high impact material as the stock, pistol grip and hand guards of the M16A2. The upper and lower receivers are to be the same as the M16A2 amongst many others.

The parts commonality requirement was troublesome to Colt engineers but they understood the government’s position. With over 7 million M16-family of weapons in service at the time, they did not want to make any dramatic changes to an already proven design. Owing to the different operating characteristics of the carbine, Colt felt there should be some changes. Due to the gas port being so much closer to the bolt, higher pressures existed in effect, significantly increasing the cyclic rate of fire. This caused issues with bolts breaking, bolt carrier bounce, failures to extract as well as feed. However, the government was very much stuck on interchangeability over durability/reliability. Colt engineers felt that a redesign of the bolt and barrel extension would significantly enhance the carbine’s performance but this would have been a major violation of the interchangeability requirement.

During the development phase, Colt engineers found certain changes that must be made for the carbine to function reliably. One of the first improvements made to the XM4 was to correct failure to feed. Due to the shape of the M855 bullet and the higher cyclic rate, the cartridge would stall where the barrel extension met the upper receiver. To correct this, both feed ramps were extended on the barrel extension as well as the upper receiver. After much experimenting with buffer designs, a new buffer was implemented to combat the bolt carrier bounce issues during burst fire. Because of the higher cyclic rate, as the bolt carrier moved forward, the bolt would lock releasing the automatic sear in turn releasing the hammer to strike the firing pin. But at that moment when the carrier struck the barrel extension it would bounce back just enough to disallow the firing pin enough clearance to strike the primer. Thus, a new buffer was adopted for use in the XM4. This new buffer (H) would remove one of the steel weights and replace it with a weight made of tungsten weighing nearly twice that of the standard steel weight. This extra mass slowed down the cyclic rate on the closing stroke eliminating the problem.

Another requirement was to have an increase in the carbine’s ability to dissipate heat, keeping the shooters hand cooler during firing/handling under normal conditions. To answer, Colt’s Henry Tatro developed a hand guard (U.S. Patent No. 4,663,875) with double heat shields.

Several other parts were modified to increase reliability such as the burst cam, stock and ejection port dust cover. The first production M4 carbines were delivered with standard M16A2 fully adjustable rear sights. This was soon to be replaced with the Mil-Std-1913 flat top upper receiver. The M4A1 carbine would only be issued with the flat top upper.

The true “heart and soul” of the M4 carbine is the Mil-Std-1913 flat top upper receiver. The Colt/ARMS, Inc. designed flat top upper receiver and dovetail is the modularity of the carbine. This enabled the use of an entire new generation of advanced optics including reflex sights, thermal sights, optical sights as well as night vision. The dovetail enabled optics to be mounted at a comfortable eye level rather than the awkward mounting of an optic on top of the carrying handle of the standard A1 and A2 sights.

The Adoption of the M4 and M4A1 carbines

On August 15, 1994 the U.S. military adopted the M4 and M4A1 carbines. The only difference between the two is the M4 has a “burst” setting and the M4A1 has an “auto” setting. The vast majority of M4A1 carbines would be manufactured for the United States Special Operations Command (SOCOM).

The military specifications were drafted for the carbines including the inspections to be performed by Colt personnel as well as the on-site government inspector. The specifications state the endurance tests and allowable malfunctions per lot. The mil-specs have also written the processes of proof testing and magnetic particle inspecting of all barrels and bolts.

As of this writing, Colt has provided the U.S. military with an excess of 340,000 M4/M4A1 mil-spec carbines with tens-of-thousands more on order. This does not include foreign or law enforcement sales.

The Finalized M4 Carbine

The M4 carbine is a lightweight (5.9 pounds unloaded), gas operated, air cooled carbine capable of semi-automatic and burst fire (auto for the M4A1). Nearly 25% of the components of the M4 are not interchangeable with the M16A2, M16A3 and M16A4 rifles. With the telescopic stock fully extended, the carbine is 33 inches long and with the stock closed, 29.8 inches. The carbine uses the direct gas or gas impingement system utilizing an “exhaust pipe” that goes from the front sight assembly (where the gas port is located) back to the bolt carrier. The expansion chamber is located in the rear of the bolt carrier between the rear of the bolt and the front of the inside of the carrier. This creates a hammer-like blow that drives the carrier rearward unlocking the bolt, extracting and ejecting the fired cartridge case. The spring loaded buffer is compressed on its rearward motion and then drives the bolt carrier group forward stripping a cartridge off the top of the magazine, feeding, chambering and finally locking the bolt into the barrel extension. The benefit of this system is lightweight and accuracy. The barrel does not have some heavy piston attached to it preventing the natural barrel harmonics affecting accuracy. The drawback is that it directs fouling into the bolt carrier. This requires more frequent maintenance with extended use and is cleaned with normal cleaning solvent and brushes. Millions of rounds have been fired through the XM4 and M4 carbines in test conditions and this carbine is the preferred weapon by U.S. Forces.

Government Procurement

Once adopted by the military and the TDP finalized, the M4 went into production in 1994. Once in production, modifications or improvements would be extremely difficult for Colt to make. Any change would have to be authorized by Rock Island Arsenal and if the military in general were pleased with the performance they would not authorize any changes, particularly ones that add new parts to the inventory or create interchangeability problems with current weapons.

Popular belief is that the M4 carbine has not been improved by Colt since its adoption. Throughout the M4 design and procurement, Colt has proposed changes and updates for the M4 only to be overruled. An excellent example is the belated adoption of the “M4 Extractor Spring” which is identified by its gold color. Colt had redesigned the spring to give significant more strength, which is a major reliability enhancement in the carbines. Rather than adopt a new spring, which Colt was installing in all of their rifles and carbines except the one being delivered to the U.S. Department of Defense, the military put M231 Port Firing Weapon extractor springs in the M4s, just so as not to add a new part to the inventory. It was not until mid 2003 that this important reliability enhancement was authorized by Rock Island Arsenal and implemented into production. During the development phase of the XM4, Colt engineers proposed modifications to the bolt and barrel extension that would make the carbine handle better when being fired with water in the barrel. This idea was rejected by the government for reasons such as a violation of parts commonality and that they could not justify the cost/benefit of the change. They felt that the number of occasions that the weapon would be called upon to fire under such conditions was minute. Colt was overruled. Colt would not revisit this reliability enhancement until the development of their SCAR entries, which had “Over the Beach” requirement.

Without the direction or request from Colt’s customer, the U.S. Government, to make changes and improvement, Colt would not invest large amounts of resources into improvements if their largest customer would not accept them. Colt had proposed changes to the Army for a redesign of the bolt and related components to increase durability and reliability. Colt estimated the two year project would cost between one-half and two million dollars. Due to lack of funding as well as lack of government interest, the project never commenced.

There are two very different types of troops using the M4 family of carbines. The U.S. forces at large are very happy with the M4 carbine and prefer it to any other available weapon. The Special Operations Forces operators have been displeased but use them in a very different way from the rest. This situation makes it difficult for Colt to address SOCOM’s needs and make modifications. The M4, coming from an existing family of weapons, caused and still causes great difficulty to design the carbine to function to it’s potential with the requirements for interchangeability and the current attitude towards making changes within the government. On March 1, 2000, the Project Manager at Rock Island Arsenal stated, “The M4A1 carbine is already 3 times as reliable as called for in the specifications.”

SOCOM Taking the M4 to the limits and beyond.

As previously stated, the M4 was to be a lightweight carbine that was to be used by people who could not carry a rifle but needed more firepower than a pistol. However, once the M4A1 got into circulation within the special operations community the compactness, modularity, ease of operation and performance was immediately seen and they adopted the M4A1 as their main weapon. They would admittedly push the carbine well beyond its design intent.

SOCOM began reporting durability issues with their M4A1 carbines including blown barrels, broken bolts, failures to extract and over heating. None of which the regular Army units nor anyone else in the U.S. military were experiencing. Investigations immediately began by Rock Island Arsenal to determine if these problems were in fact problems with the design or manufacturing process of the carbine, or if the carbine was being used beyond its design intent. At this point, Colt was not able to make any changes to the firearm without this determination. The M4A1 is procured by the U.S. Army and subjected to the TDP. Any changes or improvements requests/requirements would have to be made by the U.S. Army, not SOCOM. This is the major difference between SOCOM employing a standard issue weapon versus them procuring their own weapon. By procuring their own weapon they are the customer and can make changes as they see fit. This is the case of the SCAR but not with the M4A1.

The first major investigation found the issue regarding blown barrels was clearly due to excessive operation beyond what the carbine was designed. The M4A1 was being used as a light machine gun or a SAW (Squad Automatic Weapon) laying down large amounts of cover fire. The barrels would reach their transformation temperature that is between 1,100 and 1,375 degrees. At these temperatures the barrel becomes soft and loses its heat-treating. Structural failure is just a matter of time. According to Rock Island’s testing, to get the barrel to this temperature you would have to fire 540 to 596 rounds within 3 to 3-1/2 minutes. The average infantry soldier does not carry this much ammunition as his combat load – the average being 210 rounds. This was clearly beyond the capabilities of a lightweight carbine and Rock Island Arsenal felt that this was not a deficiency in the design or manufacture of the weapon. Due to this type of use, Colt now provides all M4A1 carbines with a heavy barrel designed by Rock Island Arsenal and improved buffer to cope with this type of use. Recent interest has been given to the superiority of cold hammer forged barrels such as that used by H&K, IMI and Glock. The question has been asked, “Why does the M4 not have a hammer forged barrel?” The answer is very simple. Colt has offered them to the government and been rebuffed. Diemaco in Canada, now owned by Colt, has made them for the Canadian military since 1983.

Many SOCOM groups have problems with maintenance of the weapons, in particular replacing worn out components. One SEAL team said they did not keep track of malfunctions during missions to report back to an armorer to have the weapons fixed. Additionally, the training weapons that these operators use are the same ones they take into combat. The barrels and bolts have an unknown number of rounds through them. SOCOM operators fire an average of 24,000 rounds per year in training alone. Most all of the criticisms regarding this weapon system have come from a small element within the SOCOM community.

This weapon system has been in use with the British Special Forces for quite sometime. The SAS use the SFW (Special Forces Weapon) manufactured by Diemaco (now Colt Canada). These specialized carbines beat out Heckler & Koch G36 (identical operating mechanism to the HK416 and the XM8) and the SIG 500 series rifles and have seen action in both Afghanistan and Iraq. Unconfirmed reports say that the British Special Forces spent more money on the test and evaluation of these weapons than they did on the weapons they procured when the award was given to Diemaco. In addition, Diemaco (Colt Canada) has been asked to quote on weapons to replace the “perfected” L85A2.

The M4 is the preferred weapon for American forces overseas and the biggest problem they have with it is that there are simply not enough to go around. Clearly SOCOM needed their own weapon that would be suited for their requirements and that did not materialize until recently with the issuance of the SCAR developmental contract. Many people in the community speculate that the SCAR competition was conducted purely to keep the Program Executive Officer Soldier from forcing the XM8 on SOCOM.

Further Advancements at Colt

Colt has now split off into two companies. Colt Defense LLC is committed to military and law enforcement sales and Colt’s Manufacturing Company focus is the commercial market.

Colt Defense LLC is dedicated to providing military small arms throughout the world to the United States military and allies as they have done for nearly 170 years. Colt Defense has been diligently working on many military programs such as the SCAR program in which they submitted three entries. The SCAR (Special operations Combat Assault Rifle) program was, without a doubt, the most grueling firearms test ever conducted anywhere in the world. It was unwritten but clear that SOCOM wanted a piston driven mechanism. Colt developed a rifle with a piston mechanism as well as two direct gas rifles. The contract was awarded to FN Herstal of Belgium. Colt’s entries came in 2nd, 3rd and 4th. These are some of the most advanced military small arms in the world. Currently, Colt is working on a submission for the OICW and has plans to introduce a piston-operated Law Enforcement Carbine in early 2006.

In May of 2005, Colt purchased Diemaco from Heroux Devtek in Canada. Now called Colt Canada, Diemaco has been a supplier of parts to Colt for several years due to Diemaco manufactured mil-spec components from the Colt TDP. With the acquisition of Diemaco, Colt will take advantage of their excellent research and development team as well as their state of the art manufacturing facility.

Some sources would lead you to believe that the future of Colt and the M4 is on uncertain ground. The reality is, however; the U.S. government has recently placed a $55,000,000 order for M4s, to be delivered within 12 months, in addition to other large quantities of M4s for delivery in 2005 and 2006. With the U.S. military looking at a replacement weapon for the M16 and M4 family of weapons, their days could be numbered. However, if history has shown us anything in the last 40 years is that the military has tried to replace this family of weapons before. The ACR or Advanced Combat Rifle program of the mid 1980s for example. This was a trial of truly advanced weapons involving new types of ammunition including caseless, duplex and flechettes. The baseline rifle was the Colt M16A2. In the end, nothing achieved better combat performance than the baseline M16A2. The M16A2 has gone on to evolve into the M16A4 and the M4 carbine and, if given the opportunity, has much life left in it. This is why this family of weapons has been around for so many years because it evolved to the changing modern combat conditions. It would be far better for the U.S. military to improve the M4 and to keep the combat proven family of weapons than to invest in a new weapon that is not compatible with any of the current optics, mounts, magazines and SOPMOD components.

Now what of the future? The XM8 is not new or advanced but based off another Stoner designed weapon from the early 1960s; the AR18. Another unanswered question is why the government is spending money on a foreign weapon development without even the rights to the design. This was an issue that Colt dealt with during the Vietnam War. The decision was made in 1968 to sell/license the government the rights for the M16/M16A1 so if need be there could be other suppliers in case of a national emergency to procure needed small arms to equip our soldiers. Will there be enough of advancement in technology to justify the change to a new weapon? It hardly makes sense since the same ammunition is used so no difference in lethality or range. The U.S. military’s current weapon systems have been combat proven in every theater in the world. The M16/M4 families of weapons have long proven themselves the hard way: on the battlefield.

With the advent of the industrial revolution in the 1800s, the foot soldier no longer carried just a pike, lance, spear, bow, sword or rifle. The rapid development of more complex mechanical weapons systems necessitated the use of small carts to move materiel right up to the front lines. World War I saw a tremendous increase in the need and use of small carts in all types of applications. Foot soldiers responsible for the newer and larger small arms such as machine guns and mortars needed a mode of transportation that addressed their needs in the field. (See Small Arms Review Vol. 3, No. 10, July 2000 for a discussion of the Model 1917 Machine Gun and Ammunition Carts used in World War I.)

The lessons learned in World War I brought about a series of rapid developments in the inter-war years to meet the demands of a rapidly changing military culture. Among the many items that were further refined were the small hand carts. No longer designed with the horse or mule as the primary means of power the new carts had to be able to withstand the demands of towing by motored vehicles over longer distances and at faster speeds and be more robust in their construction. Of course, provisions still had to be made to accommodate the last line of power: the foot soldier.

Shortly after World War I in the mid 1920s, the Mount, Wheeled, Machine Gun, M1 was developed for the dual purpose which combined the idea of a T base (trail assembly) for the M1917 tripod with that of a two wheeled light weight cart for transportation of the Browning M1917 water cooled machine gun, accessories and ammunition in the set up and ready to fire configuration. The idea being that the set up gun could be quickly brought to use and fired from the cart if need be or the soldier could quickly dismount the gun and tripod and set up in a position without having to assemble the components. A third option was to leave the gun as set up and remove the wheels and simply drop the entire T-frame with the mounted gun on the ground. This method was viewed as especially valuable in sand or soft earth conditions that without it the tripod feet would bore into the ground and the gun become unstable. The M1, the first post World War I hand cart, was a simple T-shaped affair with solid rubber coated wheel rims and a simple bracket to hold extra ammunition boxes.

Quickly on the heels of the development of the Cart, M1 were the Cart, M2 and Cart M2A1. These carts were basically updated versions of the old wooden M1917 Ammunition Carts in that they were still designed to be drawn primarily by horse or mule but were constructed of metal rather than wood. The Cart, M2 was issued for transporting .30 caliber machine gun ammunition, 37-mm gun ammunition, light mortar ammunition and communication equipment. The Cart, M2A1 is the identical cart as the M2 except that it has front and rear brackets specifically for transporting the 81-mm Mortar and Bipod Mount M1.

Next in the litany of hand carts developed in the 1930s were the Carts, Hand, M3 and M3A4 (utility), M4 and M4A1 (.30 caliber machine gun), M5 and M5A1 (.50 caliber machine gun) and the M6 and M6A1 (81-mm mortar). They consist of two types and are of four purposes. The first (earlier) large wheeled type have 4” x 18” motorcycle wheels on a straight axle and are identified by the designations M3, M4, M5 and M6. These carts were classified as limited standard during World War II. The second or small wheel type have 4” x 12” cast aluminum wheels on an offset axle and are identified by the model designation M3A4, M4A1, M5A1 and M6A1. These carts were classified as standard during World War II.

The carts are drawn by man power but are equipped with a lunette for limbering to a Jeep or other small vehicle. When drawn by man power a drawbar is secured to the lunette with the hand cart drawbar retaining pin. When not in use the drawbar is carried on the drawbar bracket which is riveted to the front body. Provision is made for attaching tow ropes with D-handles to the cart body when additional man power is required to pull the load. The carts are also designed so that two loaded carts can be transported on trucks when placed between the seats provided for personnel.

The M3 and M3A4 utility hand carts are comprised of the chassis and body. The chassis of the M3A4 small wheeled cart is composed of an offset axle, tongue and drawbar assembly. The axle is an aluminum-alloy tube and assembled on each end are aluminum-alloy axle brackets that are riveted to the axle. Steel spindles, to which the wheels are mounted on anti-friction bearings, are assembled in the axle brackets and secured by nuts and cotter pins. The axle brackets are fastened to the side and bottom of the cart body by bolts. The tongue is an aluminum-alloy tube reinforced by a liner made of the same material. The spade lunette is riveted to one end and the tongue and axle bracket which fastens the tongue to the axle to the other end. The tongue is secured to the front of the body by a clamp. The body, which is the same for both the large wheeled M3 and small wheeled M3A4 carts, is a rectangular shaped open box which is bolted to the chassis. The M3 body is constructed of aluminum channels and rails reinforced with angles and gusset plates held together by rivets. The M3A4 body is made of steel and does not require the reinforcing angles and gusset plates. Holes are drilled in the body of both the M3 and M3A4 to bolt the brackets which are required to convert this cart for its other uses.

The M4 and the M4A1 .30 caliber machine gun hand carts are converted from the M3 and M3A4 carts respectively by the addition of three brackets to which the legs of the M1917A1 tripod mount are attached. The Browning .30 caliber M1917A1 water cooled machine gun, which is used on this mount, can then be used as an anti-aircraft gun or the gun and mount can be quickly removed to be used as a ground gun. Leather straps are also provided to hold spare ammunition boxes and accessories.

The M5 and M5A1 .50 caliber machine gun hand carts are also converted from M3 and M3A4 carts respectively by the addition of brackets to receive the Browning .50 caliber M2HB, flexible and the M3 tripod mount during transit. Unlike the .30 caliber set up, the .50 caliber is transported in a disassembled state though the brackets are equipped with quick release clasps to facilitate speedy unlocking. A leather strap is provided to secure the ammunition boxes.

The M6 and M6A1 81-mm mortar hand carts are also converted from M3 and M3A4 carts respectively by the addition of brackets and supports to secure the 81-mm mortar M1, and 81-mm mortar mount M1 during transit. Quick release clamps and leather straps are also provided.

Though there are a number of “M” designations for the cart, the basic M3A4 Utility Hand Cart fulfilled a vital need in the war effort by easily being converted to a number of uses merely by the selection of clamps and brackets.

The carts were manufactured in the tens of thousands (some estimates go as high as 70,000) by Rock Island Arsenal, John Wood Manufacturing, Trussbilt Incorporated and Omaha Industries. Yet, only about a hundred or so are accounted for today in conditions ranging from rusted out basket cases to restorable examples. The carts did not have a priority for return after the war and were left wherever they were to pretty much rot away. They were used extensively by the Army and Airborne units in Europe and by the Marines in the Pacific. (As an interesting side note, in the movie “The Longest Day”, John Wayne, playing Col. Benjamin Vandervoort of the U.S. 82nd Airborne Division, breaks his ankle when jumping into France on D-Day and is hauled around on a M6A1 mortar configured cart.)

By Bob Campbell

Within the framework of the AR 15/M 16 rifle there are subtypes that are very interesting, perhaps even more useful than the original gun. One of the most popular, a weapon of almost legendary reputation, is the CAR 15/M 177 or M4 Carbine. The first short barrel short stock M 16 variants appeared in the late 1960’s. They met with varying degrees of success. I’ve fired most, a notable exception to my experience being the ‘port firing’ M 16’s designed for use within armored vehicles. Early guns in the CAR 15 series were sometimes called Commandos. The original guns coupled a ten inch barrel with a folding or collapsing stock. Colt had wished this line to be known as the CAR 15 line to signify the difference between Colt and Armalite production.

The short XM 177 received and kept the CAR 15 tag. These guns were criticized on several points, especially reliability. Col. Tony Herbert, the most decorated enlisted man of the Korean conflict served as a officer in Vietnam. He found the M 16 was a fine rifle, well suited to the conflict, but derided the CAR 15 as unreliable. He felt it had more show than performance, likening its image to that of the Thompson submachinegun of another war. The XM 177E2, with a longer 11.5 inch barrel and other types of ‘tweaking’, proved more reliable.

The XM 177E2 was dropped from production. The early short M 16’s were plagued with reliability and ammunition performance problems.

Later carbines were developed which featured 14.5 inch long barrels. These longer barrels work much better with the M 16 gas system and retain more of the 5.56mm cartridge’s effectiveness. This is a round that relies upon high velocity for effectiveness. Wound ballistics are compromised when the velocity falls below 2,500 fps. With enhanced ammunition performance and increased reliability, later variants such as the 1980’s M 16A2 carbine were much more effective weapons. Many in the Army wished to adopt the Carbine as a standard weapon but it remained for the most part a special team weapon, often issued to drivers and dog handlers or other needing a short light weapon. It is much more effective than any handgun or submachinegun, weapons often assigned this task.

The M4 and M4A1 are recent variants, being adopted in 1994. Both are in wide use by all of the services. Two models are in use. The M4 has the familiar ratchet-type three shot burst limiter. When the weapon is on full auto, it can be fired only in a three shot burst mode. At least in my hands, the usual result is two shots close together and one with greater dispersion. The M4A1 has the more conventional mode of fire.

A trained operator can tickle the trigger well enough to fire two to four round bursts in full auto mode. The trick is in training, a greater indicator of success in the field than gear. The M4’s currently in service are flat-top models, or M 16 variants with removable carrying handles. These weapons may easily be fitted with telescopic sights.

The M4 type weapon is also popular with civil agencies, especially Special Weapons and Tactics units. The needs of mobile SWAT teams are well served by the M4. The M4’s 14.5 inch barrel is not civilian legal, but a number of approximations are available with legal length 16 inch barrels. They mimic the M4 in a reasonable manner, of course without the full auto option. I’ve fired quite a few and they are accurate, reasonably compact weapons. Several versions are offered by Wilson Combat. Not as well known for his rifles, Wilson’s rifles and carbines are world class weapons.

The true M4 exhibits the following features—

• 14.5 inch, 1 in 7 inch twist barrel
• 7 3/4 inch round handguard
• Double heat shield
• Flat top receiver
• Four position buttstock—Closed/Full open/one half and three quarters open.

Early ammunition problems with the CAR 15 type guns are well documented. Often, downsizing a weapon does not work as well as the designer had hoped. M4’s currently in use feature an increased diameter gas port, which aids in overall function.

The M4 carbine has been well received in service, passing stringent testing. It is used by airborne units, SEALs, and other special operators.

Notably, the availability of the M4 carbine has resulted in less utilization of other weapons such as the Heckler and Koch MP5 and other weapons. The M4 can perform the same tasks but arguably much better, while fulfilling the mission envelope of the M16A2 as well.

The carbines are six inches shorter than the M16A2, a significant advantage when parachuting or traveling in a raft, and an advantage in house clearing as well.

The problems encountered by Israeli and Palestinian forces in house clearing with the M16 and Galil are well known. The UZI found favor with the Israelis. They would not allow Palestinian forces to use the UZI. The UZI is a good weapon of the type, but not comparable to the M4.

The question of accuracy and lethality remains with the M4. Accuracy to even 500 yards is comparable to but not equal to the M16A2. I have fired several short carbines at length. I chose Black Hills ammunition for the chore. Since their match grade loads are used by Marine sharpshooters, it felt appropriate. I used not only standard 55 grain loads but the 52 grain match load, the 60 grain softpoint, and a 68 grain match load. Results were very good. At 100 yards-and infantry engagement range is held to be one hundred to one hundred twenty five yards-accuracy was excellent.

The .223 cartridge must retain 2,500 fps or more of muzzle velocity to retain its lethality. With short submachinegun type barrels as seen on the CAR 15 this was not always possible, but it is a non issue with the M4.

The M4 provides an excellent alternative to the M16A2, with many good features and few tradeoffs. It is a fine weapon for the 21st century warrior.

Colt’s M4 and M4A1 carbines will soon be the standard arm of the US airborne and special operations forces, where they will replace the M16A2. The venerable Heckler & Koch MP5 submachine gun is also slated to be replaced in special operations forces by the subject of this article, the M4A1 Close Quarters battle (CQB) Weapon. The M4 is essentially an M16A2 with a 14.5 inch (368mm) barrel, while the M4A1 is the shortened version of the “flat top” M16A3. The primary differences between the M4 and M4A1 are the detachable carrying handle/rear sight assembly of the latter which is mounted on a MIL-STD-1913 “Picatinny Rail” and the fact that the M4A1 is capable of full automatic fire rather than having the M4’s three-round burst feature. The M4A1’s MIL-STD-1913 rail mounting system allows the flexibility of quickly mounting various optical sights and other accessories without losing weapon zero. Also, the devices are generally mounted in a position that does not demand that the shooter crane his neck to see through them, as is the case with fixed carry handle AR-15 type rifles and carbines.

While the M4A1 offers more flexibility than the standard M4, the weapon’s users desired even more flexibility – a truly modular weapons system capable of being configured for optimum effectiveness in any tactical situation. The US Special Operations Command (USSOCOM) synthesized the inputs and requested Crane Division, Naval Surface Weapons Center, to develop the system that eventually became the Special Operations Peculiar Modification to the M4 Carbine Accessory Kit. This piece of bureaucratic jargon is abbreviated SOPMOD M4, but it is probable that many who use the term are unaware exactly what comprises the kit, to whom it is issued and how it is employed. Essentially, joining the SOPMOD M4 Accessory Kit to the M4A1 Carbine results in the M4A1 Close Quarter Battle Weapon. We should note at this point that the Army has experimented with a carbine designated M4E2 that is essentially a burst fire M4A1 with the rail interface system described below.

The purpose of the SOPMOD M4 kit is to provide the US special operations forces with the ability to adapt their weapons to meet virtually any mission profile. This is necessary because SPECOPS units have no heavy weapons and thus must optimize the operational effectiveness of the weapons that they have. The SOPMOD M4 kit allows the user to “tailor” his weapon to the assigned mission. The kit is intended to optimize the effectiveness of the M4A1 from CQB/CRE range of less than 50 meters out to the 600-meter maximum effective range of the weapon. While the components of the SOPMOD M4 kit are current as of the time of this writing (July 1999), it is probable that they will change over time, as the kit is intended to evolve to take advantage of technology developments that enhance the effectiveness of the M4A1. (Some are currently under development and will be reported upon in SAR in the near future.) Unlike many other military requirements, development of new items for the M4A1 does not require a change to the requirements documentation. This enables USSOCOM and Crane to act rapidly to bring new items into the inventory. It is significant that virtually all components of the SOPMOD M4 kit are nondevelopmental items/commercial off the shelf (NDI/COTS), are available in the open market and can be mounted on any AR-15 – type carbine. As we explore the components, the reader can determine which of the SOPMOD M4 Kit components, he or she might like to add to their CAR-15 or equivalent. Most of these components will also fit an M16A4 configured AR-15-type rifle, as well. (The M16A4 configuration simply is an M16A3 flattop rifle length with the Knight’s Armament Systems Rail Adapter System (RAS), M5, full-length handguard.)

SOPMOD M4 Kits are issued on the basis of one kit per four carbines and consist of four of the following components: Rail Interface System (RIS), optical scopes, forward vertical hand grips and combat slings. Other items such as the reflex sight, suppressor and Quick Attach M203 are intended to be fitted to one or two carbines out of every four. While the basic “one kit per four carbines” is a general rule of thumb, if more of some items are required, shortfalls are made up from kits which are not required by other teams. Present issue is three kits per Army Special Operations Forces “A” Detachment (SFOD-A), two kits per “B” Detachment (SFOD-B), three kits per Air Force STT and four kits per Navy SEAL platoon. Army Rangers and other special mission units are issued selected components rather than complete kits.

As previously mentioned, the requirements documentation that resulted in the current SOPMOD M4 Kit is written to accommodate changes and upgrades, generally without rewriting. As technology, threats, missions and requirements change, the kit will likewise evolve to keep pace with them. Capabilities that are within those originally identified in the original requirements document do not require rewriting. That is, if a new or improved item is developed that is a significant improvement over an existing component of the SOPMOD M4 Kit, no rewrite of the original requirement is necessary, nor is any change required. If, on the other hand, the capability is a new one beyond the scope of the original documentation, the capability must be validated by USSOCOM and the requirement modified. Once the requirement is validated, the program office at Crane will conduct a competitive evaluation of candidates for selection. Now that we understand the M4A1 Carbine and the overall concept of the SOPMOD M4 Kit, we can proceed to the heart of the matter – the components that make up the kit. First, the basic SOPMOD Kit for four carbines consists of the following components in the quantities indicated in the chart on the top of page 26.

A detailed description of these components and their use is the subject of the remainder of this article. The first is the Day Optical Scope (DOS), Trijicon’s Model TAO1NSN 4x32mm Advanced Combat Optical Sight (ACOG). The DOS is intended to extend the carbine’s effective range to 600 meters. This version of the ACOG has the Bindon Aiming Concept reticle as standard. This system is similar to that used so many years ago by the Germans and to that espoused by Jeff Cooper for his scout rifle concept. The system uses a low power telescope and the “both eyes open” aiming method. As the rifle is brought to the shoulder, the image is unmagnified, permitting extremely rapid target acquisition. Once the rifle is in a shooting position and the shooter is close to proper sight picture with the optic, the target “snaps” into magnification, providing not only faster target acquisition, but also greater accuracy. The central crosshair reticle of the DOS is illuminated by tritium and gives off an amber glow for use in low light or darkness. The wavelength of the amber light is beyond those which night vision devices can sense and so does not affect their use. The DOS is waterproof for eight hours at 66 feet (20 meters) depth.

The 2.25x Miniature (Mini) Night Vision Sight (MNVS) is a small, lightweight and compact night vision sight that provides the capability to identify and hit targets from 20 to 300 meters. The sight is adjustable for windage and elevation and may be mounted on the carbine or hand held. The MNVS reticle is a simple red light emitting diode that subtends 2.5MOA at 100 yards. The sight weighs only 1.85lb (0.83kg, is 7.5in (190.5mm) in length and is powered by a single “AA” size alkaline battery that has an operational life of approximately 16 hours.

The SOPMOD M4 Kit also includes Trijicon’s ACOG Model RX01M4A1 Reflex Sight under the nomenclature Reflex Sight (RS) as a compliment to the 4×32 sight described above. The RS is a 1x day optic intended primarily for CQB/CRE ranges while still enhancing target acquisition and accuracy to a range of 300 meters. Like the 4×32 sight, the RS uses tritium to illuminate the reticle dot for low light and night operations. The dot is also illuminated by ambient light through a fiber optic cable that gathers light from beneath the lens. The collimator system eliminates parallax, so that if the dot appears on the target, it is properly aligned, regardless of the angle from which it is viewed. The design of the sight also provides for a virtually unobstructed view of the target. Like the DOS described above, it allows the shooter to employ the “both eyes open” aiming technique that enhances speed and accuracy at all ranges. The amber dot of the RS is identical to the DOS reticle frequency and thus is fully compatible with all night vision devices. The RS can be mounted either on the receiver rail or forward on the Rail Interface System, at the option of the user.

The question of why amber versus red reticles were used may be raised by some readers and the answer is because of night vision. Simply stated, amber is less destructive of night vision capability than red. The human eye is actually “night blind” at its exact center, where vision is sharpest. This is why, in the days before night vision devices, infantrymen (this writer included) were trained to observe at night without directly scanning the terrain and then to focus once something was detected. The rods that provide night vision are not affected by the amber glow, which is normally centered in the “night blind” area of the eye. In addition, of course, the amber color of the SOPMOD M4 sights do not affect night vision optics. The RS is issued with a polarizing filter for use under special conditions or with a flashlight, where it improves aiming dot contrast. The filter is not compatible with night vision devices. The RS is also issued with an accessory dust cover for use in extreme conditions.

When the carrying handle/rear sight assembly is removed, the military recommends that the Backup Iron Sight (BIS) be installed at all times. This is an excellent policy because although modern optical sights are extremely reliable, one of Murphy’s Laws of Combat dictates that the most critical piece of gear will “go south” at the most inopportune time. Moreover, optical sights are complicated devices and thus susceptible to the “breakdown” law, while “iron” sights are about as simple as aiming devices can get. The sight used in the SOPMOD M4 Kit is simply clamped at the last notch of the receiver rail and folded down out of the way unless it is needed. The BIS is adjustable only for windage in .5 MOA increments. Elevation is adjusted using the front sight. The BIS is intended for use from CQB/CRE range to 300 meters. Once the BIS is zeroed, it can also be used to obtain an approximate zero for other accessory sights, although shooting with sights “zeroed” in such a manner is recommended only to a maximum of 100 meters.

The Knight’s Armament Company Rail Interface System (RIS) is a key component of the SOPMOD M4 Kit because it allows the mounting and operation of many of the kit components, including lasers, visible lights, the vertical handgrip and more. It is safe to say that without the RIS, the versatility and flexibility of the SOPMOD M4 Kit would be dramatically reduced; the RIS is truly the “core” of the SOPMOD M4 Kit. The RIS concept is a simple one. The system consists of two 6061 T6 aircraft aluminum hard anodized coated sections that replace the standard upper and lower M4A1 handguard sections. Upper and Lower RIS sections are not interchangeable. The lower section has a single MIL-STD-1913 rail and the upper has three such rails, 90 degrees apart, thereby providing four equally spaced rails when the RIS is installed. The top rail is slightly higher to align it with the top of the receiver. The RIS lower section has an aluminum heat shield on its inner surface. When there are no SOPMOD M4 Kit components mounted on the RIS, glass filled nylon rail cover panels are slid into place over the rails to provide a relatively even grip surface. The panels are available in varying lengths so that there is an even grip surface, even when accessories are installed.

The Forward (vertical) Hand Grip, another Knight’s product, is installed at approximately the mid-point of the lower rail, depending on the user’s preference. The Forward Hand Grip provides better control of the carbine, especially when several accessories are mounted on the RIS. It also provides additional insulation when the carbine is being fired on full automatic.

The Insight Technologies Visible Light Illuminator is a very high intensity rail mounted light intended for search and clear operations in what the army currently euphemistically describes as “military operations other than war.” In plain English, this means “peacekeeping” or other “pizza delivery” missions which presently seem to occupy the preponderance of our military’s efforts. Tactical use of “white lights” must, of course, be balanced against revealing one’s position. The visible light is sufficiently bright, however, to briefly dazzle adversaries in CQB/CRE situations, thus providing a moment’s advantage to the user. An infrared (IR) filter may be placed over the light to allow IR illumination of targets out to 50 meters. The light is powered either by three DL 123 lithium batteries or by six 1.5 volt “AA” size batteries.

The Insight Technologies AN/PEQ-2 Infrared (IR) Target Pointer/ Illuminator/Aiming laser allows the carbine to be used with any one of several night vision optics, including the standard head mounted goggles, a head or weapon mounted pocketscope, or the issue Mini Night Vision Sight (MNVS), described elsewhere. It is intended for use inside buildings and elsewhere where vision using the NVG would be problematic due to lack of available light. A neutral density filter that prevents “blooming” is used with the laser at close ranges.

Insight Technologies’ AN/PEQ-5 Visible Laser is mounted on the rail interface system and is used for close range engagements. The intent is not to replace the optical sights, but to supplement them in interior lighted areas or in dark rooms in conjunction with the visible light illuminator, or at night in conjunction with night vision equipment.

The Knight’s Armament Company sound suppressor is designed for quick attachment/detachment and reduces the M4A1 noise signature at the muzzle by approximately 28db. The suppressor also significantly reduces the flash signature. Taken together, the sound and flash reductions not only confuse adversaries, but also enhances team communications and reduces the need for hearing protection.

The M203 Mount and Leaf sight, although capable of being quickly and easily attached or removed, are rarely dismounted once they are installed on a particular carbine. Other than its shorter barrel, the M203 is identical to the version used with M16 rifles.

A special sling that provides secure cross body or patrol carry is used with the M4A1 CQB Weapon. Whether in column, “stack,” or moving in close quarters, the sling helps the user maintain control of the weapon’s muzzle. The sling has a removable mount that attaches at the front sight/gas block or to the rail interface system. The sling does not interfere with any components that may be mounted on the rail interface system.

Finally, the enhanced collapsible stock improves the M4A1 CQB Weapon’s ergonomics by enhancing the cheek weld for improved pointing at close range and enhanced aiming at any range. The stock also has compartments to accommodate spare batteries for kit accessories.

One of the keys to the success of the SOPMOD M4 Kit is the fact that the vast majority of its components are commercially available. As mentioned above, most can be purchased commercially by any owner of an M16/M4 type carbine who wishes to create a truly modular firearms system. Thus, any agency wishing to equip itself with M4A1 CQB Weapons can do so by modifying their existing M4/M4A1 – type carbines, regardless of manufacturer. Contact information for manufacturers of selected SOPMOD M4 Kit Components is included below. We do not include carbine contact information in this list, as ArmaLite, Bushmaster, Colt and Knight’s all produce carbines suitable for modification into SOPMOD configuration.

ACOG Reflex Sight
and ACOG 4x Scope
Trijicon, Inc.
49385 Shafer Ave.;P.O. Box 930059
Wixom, MI 48393
Tel:248-960-7700; Fax: 248-960-7725
On-line: www.trijicon-inc.com

Visible laser, AN/PEQ-5;
IR Laser Pointer/Illuminator,
AN/PEQ-2; Visible Light
Insight Technologies, Inc.
10 Tinker Ave.
Londonderry, NH 03053
Tel: 603-626-4800; Fax: 603-626-4888

Rail Interface System; QD Suppressor; Forward hand Grip; Backup Iron Sight; M203 Quick Detach Bracket
Knight’s Armament Company
7750 9th Street, SW
Vero Beach, FL 32968
Tel: 561-562-5697; Fax: 561-596-2955

The author wishes to express his sincere appreciation to LTC Mike Harris (Ret) whose assistance made this article possible.