The OICW Increment 1 program commenced in 2005 to replace the current fleet of M16/M4 carbines in the U.S. government inventory: something that has been attempted many times without materializing over the last 40 years. This program had a requirement for a family of weapons and was broken down into three increments. Increment 1 was comprised of the family of weapons. This required a special compact model, a carbine, a designated marksman rifle and a light machine gun. Increment 2 was to be the development of the 25mm grenade launcher. Increment 3 was to be the combining of the two for the creation of the OICW (Offensive Individual Combat Weapon).

Several requirements were made in the solicitation. Most importantly, there needed to be 75% parts interchangeability in the special compact, carbine and designated marksman rifle and 50% parts interchangeability with the LMG (light machine gun).

Colt design engineers had a well-established starting point for their family of weapons. Just being post-SCAR development (Special forces Combat Assault Rifle); Colt already had a proven gas piston operated firearm and, additionally, already had a proprietary 1-piece upper receiver that would work well in all four weapons. The only major undertaking would be adapting the 1-piece upper receiver to the LMG variation.

The upper receiver for all four weapons would be based on the current LE1020 upper receiver, which is the product-improved version of Colt SCAR entry. The major change to the upper receiver would be the way the piston assembly is removed. On the SCAR rifle, there was a pin that held the piston assembly into the receiver that required a drift punch and a hammer to remove. Based on the criticism of difficulty in disassembly from SOCOM, Colt redesigned this with a sliding detent pin similar to the rear takedown and front pivot pin of the lower receiver. There was also a major redesign of the gas piston sleeve. The SCAR gas piston sleeve had no provision for easy alignment for assembly or griping method for removing an extremely fouled or corroded gas piston sleeve. The improved gas piston sleeve provided a guide for assembly to align the gas piston sleeve with the detent pin as well as a gripping surface for removal of a fouled or corroded gas piston sleeve.

The lower receiver of the OICW would be entirely interchangeable for all four models and is identical to that of the M4 carbine. The thought on this was twofold. First, the Colt OICW could be implemented as a ret-rofit of existing weapons by only replacing the upper receiver and, second, was the compliance with the parts commonality.

The LMG Variation

The LMG variation had some additional requirements to set it apart from the other three weapons that included the ability to have a heavy quick detachable barrel that did not need to have an ability to mount a grenade launcher. However, the LMG did need to have an ability to mount a bayonet. Also, the LMG was required to have a folding bipod.

The lower receiver of the LMG was the standard M4A1 lower receiver. Due to it being a light machine gun, Colt engineers took several trigger designs into consideration. They looked at an open bolt trigger mechanism; a closed bolt semi-auto/open bolt auto trigger mechanism, as well as the standard closed bolt trigger mechanism. The final decision was made to go with the standard closed bolt trigger mechanism; made primarily to keep with parts commonality. The only other departure from the norm was the replacement of the H buffer with the H2 buffer. The H buffer contains two steel and one tungsten weight and the H2 buffer contains one steel and two tungsten weights. The tungsten weight has the mass of two steel weights. This was changed to prevent bolt carrier bounce/light strikes when firing fully automatic.

As stated above, the upper receiver would be based on the 1-piece upper receiver. This receiver allowed the barrel to free-float, which in turn allowed more rapid cooling. Additionally, the upper receiver does not have a forward assist assembly. This has always been a controversial issue. Many believe, including Gene Stoner, that the forward assist was not necessary on the firearm and in fact detrimental. If your bolt is not fully closed, the rifle is trying to tell the user there is a problem! That means to get that round out of the chamber and load another. Forcing the bolt closed massively increases the potential of causing further problems. Others believe this is necessary to have the ability to force the bolt closed if need be. The forward assist has been retained due to it being required by the U.S. military Technical Data Package (TDP). However, Colt decided to remove it on this LMG.

The upper receiver is very similar to the standard 1-piece upper but with two major changes. Due to the requirement for the removable barrel, a locking mechanism had to be designed. The main changes would be made to the bottom of the handguard. The upper receiver and barrel extension are cut with the M4 extended feed ramps.

The 18.5 inch long heavy barrel has a diameter in-between that of the M4A1 heavy SOCOM barrel and the standard Colt open bolt LMG. The chamber area of the barrel has significantly more material making it much thicker and therefore increasing the LMG’s cook-off thermal threshold. The prototype LMG is set up for the 700 to 950 round per minute cyclic rate that is the same as the standard M4 carbine. The rear of the barrel would have two sets of index grooves. The first is at the rear of the barrel, which aligns into the upper receiver and acts as the barrel extension. The second is forward where the barrel is locked in place by the lever on the bottom of the receiver. To release the barrel, a lever on the bottom of the handguard is pulled out of engagement and the barrel is pulled out. This led to another problem: how the hot barrel would be removed, as asbestos gloves are no longer used or allowed. Colt was in the process of making a carrying handle to push the barrel out of the receiver right when the program was cancelled.

The gas system would also have to be modified from its original configuration. The piston/operating rod would be split into two separate pieces. The operating rod, spring and stop would be held captive in the upper receiver along with a new heat shield. This would be removed by an additional lever on the bottom of the lower handguard. The piston would be pinned into the gas piston sleeve and remain part of the barrel assembly. The gas piston sleeve is held into the front sight base in the same manner as the rest of the Colt OICW family of weapons by the detent pin on the front sight base. The piston pin is held in pace by an extended front sight base guide. To disassemble the piston assembly, the detent pin is pulled from the right, and the piston sleeve is removed from the front of the front sight base. The piston retaining pin is pushed out one of the two sides and the piston is removed from the sleeve.

The assembly of the LMG is as follows. Insert the heat shield, operating rod, spring and stop assembly into the upper receiver from the front of the receiver. Push it inward until it snaps into place and is held by the lever. Insert the piston into the piston sleeve and align the hole in the side of the piston with the channel groove in the gas piston sleeve and insert the retaining pin. Now slide the gas piston sleeve assembly into the front sight base and align the locating pin with the groove on the right side of the front sight base and push the detent pin in until it locks in place. Slide the barrel into the upper receiver (with the bolt carrier group locked to the rear) until it stops. Flip the locking lever back so it is flush with the receiver. Give the barrel a tug to be sure it is locked in place. The LMG is now assembled and ready to fire.

The bolt carrier group is identical to that of the LE1020 and the other three OICW weapons. It is a modified fully automatic bolt carrier with two major changes. The first is the addition of the “skis” on the bottom rear of the bolt carrier sear trip area. This is to keep the bolt carrier in alignment with the buffer extension when it moves rearward. This is necessary due to when the piston rod strikes the bolt carrier key as the rear of the bolt carrier has a tendency to tip down at a slight angle. The other change is the modified carrier key. The carrier key is solid steel and pinned in place to take the force of being struck by the operating rod. No gas rings are necessary. The bolt is the standard M4 bolt with the heavy extractor spring and stronger (black) extractor spring buffer.

The LMG was equipped with the standard Colt folding front sight base used on the SCAR Type C and the LE1020, and the Matech back-up iron sight; though any backup sight could be used. With the Mil-Std- 1913 rail any of the wide array of combat optics could be mounted. Due to having quad Mil-Std-1913 rails, the LMG could be equipped with a variety of accessories to include a flashlight, laser, vertical pistol grip or anything else that was wanted or needed. The LMG standard feeding device was to be the standard M16/M4 magazine, but it could also accept the Beta C-mag or any other high capacity magazine.

The program was cancelled in November of 2005. The prototype shown in this article is the only one in existence and was never finished. The bayonet lug and the barrel removal handle were never implemented.

Editor’s Note: Subsequent to this article being written, it should be noted that Colt Defense LLC has purchased the Logistics & Defense Division of Heroux-Devtek, Inc., which includes Diemaco. Diemaco will be operated as Colt Canada Corporation, a wholly owned subsidiary of Colt Defense. – Robert G. Segel

As production of standard C7 and C8 weapons went on, it was decided by the Canadian Forces that they wanted to have a platform to enable them to mount optics on the weapons. Traditionally, it has been very uncomfortable to mount a scope on an M16 rifle due to the height of the scope on top of the carrying handle. Not only was it an unnatural way to shoot, it exposed more of the shooter’s head than was desirable. This upgrade was not to be just for specialized units, but for the entire fleet. The Canadian Forces were about to equip every weapon with an optical sight.

Diemaco went to work on the development of an integrated flat top upper receiver. The Canadians decided on a modified Weaver rail that does not conform with the American Mil-Std-1913 rail for one clear reason, it did not exist yet. Their research and development pre-dated the adoption of the mil-std-1913 rail. Numerous methods to attach the rail were tested including (vacuum bonding) gluing it to a modified upper receiver – but for obvious reasons the preferred way would be to have it machined out of a single forging. It took a couple years to finalize their design. Richard Swan, of ARMS, Inc. was called in to assist with the design of the dovetail. ARMS has had many years of experience in the design of dovetails and many were in use by American Forces.

The C7A1 and C8A1

The new weapons would be type-classified as the A1 variations of the C7 rifle and C8 carbine. Canada did not convert C8’s to C8A1 until quite recently. Diemaco used the term A1 to identify carbines with flat top receivers used in other countries such as Holland. The Danes call their C8A1 the M96 Karbine. These weapons would enter service before the Colt release of the Mil-Std-1913 rail. This was a conversion process to existing C7 rifles and mandated for all future small arms production. The standard rifle and carbine barrel assembly would be used without modification. This enabled current C7 and C8’s to be converted to the new configuration by just replacing the receiver itself.

Diemaco also designed two different iron sight capabilities. The first is a primary iron sight, which is a removable carrying handle similar to the Colt designed removable carrying handle on their M16A2 Enhanced rifle and their ACR candidate. This carrying handle would maintain the standard adjustable for windage only rear sight. Additionally, an emergency back-up sight was developed that would serve as a back-up if the optic was to become damaged and inoperable. The final design was made of nylon ST super tough plastic and would mount in front of the optic.

The optic chosen by the Canadian Forces was manufactured by another Canadian firm, Armament Technologies who had also designed an optic for Colt during the Advanced Combat Rifle program. These sights were first designed by Ernst Leitz Canada, which made Leica Cameras, heavy gun and tank sights, and other equipment that required quality precision optics. The company was purchased by Texas Instruments and renamed ELCAN Optical Technologies. It is now owned by Raytheon. The C79 optical sight was an extension of a program for a sight intended for the old C1A1 FAL rifle, updated for the C7A1. The United States forces now uses this optical tube assembly in the M149 sight that they now use. ELCAN also makes all IMAX and PANAVISION camera and projector lenses, inertial guidance muti-facetted mirrors for Maverick missiles and many other military optics. This firm employs about 600 people grinding and coating optics and manufacturing mounts making every kind of optical, night vision and thermal equipment imaginable for military and civilian applications.

The C7A2

In 2003, the Canadian Forces implemented a mid-life upgrade to the C7A1 and C8A1 weapons that included being more compact, versatile and ambidextrous as well as better suitability to accept new attachments such as laser sights, flash lights, etc.

The C7A2 would omit the fixed stock. All weapons would utilize a telescopic dark green stock with 4 adjustable positions and an anti-slip butt pad enabling the rifle to be more compact to carry. With this switch, a new buffer was used which is identical to Colt’s “H” buffer that replaced one of the standard steel weights with a tungsten weight. This additional mass eliminated light strikes caused by the bolt carrier bouncing back off the barrel extension during automatic fire. A dark green pistol grip replaced the black one.

The upper receiver is the standard flat top upper with the 20-inch barrel. This was left in the 20 inch length for a simple reason; to maintain the ballistic capability of the NATO standard 5.56mm ammunition it was expected to employ. By maintaining the long barrel, the cyclic rate is reduced from the carbine variations and increases reliability due to a lower cyclic rate. This also extends the life of the bolt and other trigger components. If the weapon was to be reconfigured from the C7A1, the upper receiver would be left alone but would have new dark green handguards installed with a Triad 1 attached to the front sight assembly. The Triad 1 offered left, right and bottom rails that enabled the attachment of laser, flash lights and other equipment.

The other main improvement was making the weapon as ambidextrous as possible. The ambidextrous magazine catch was designed by another firm (NORGON) and Diemaco obtained a licensing right to produce the catch assembly in the factory. Other improvement features included an ambidextrous charging handle release lever and selector lever.

The LSW (Light Support Weapon)

The LSW began life as a Colt design of a light support weapon based on the M16 weapon system. This open bolt firing version was designed by Colt’s engineer Henry Tatro. The Colt design was never able to leave the development stages due to a labor strike and inability to free up resources to get a new project off the ground. Diemaco was called in to see if it was a project they were interested in and if they would have the resources to complete the project and get it ready to sell. Diemaco was a perfect company to take on this project due to their engineering capability and relatively small size.

Diemaco made some improvements to the open bolt fire mechanism and updated the design with some of the new M16A2 features including the new stock, pistol grip and lower receiver as well as new fully adjustable rear sights. Diemaco would also make major improvements to the barrel assembly utilizing an extra heavy hammer forged barrel, redesigned interchangeable handguards, a large foregrip that can be used as a monopod, a QD bipod, and a redesigned carrying handle. Diemaco additionally redesigned the gas tube to a larger diameter to deal with the heat of an extended firing weapon. Diemaco also put the finishing touches on a Colt designed hydraulic buffer which slowed the rate of fire down to less than 700 rounds per minute. Diemaco has sold this weapon to customers including Denmark and Holland. This weapon is made in both fixed carrying handle and flat top variations. Diemaco has also produced this weapon in a closed bolt selective fire configuration as requested by the Royal Dutch Marines and Denmark.

The SFW (Special Forces Weapon) Diemaco’s Crown Jewel

The British Special Forces began a search for a weapon that would replace their problematic SA80 assault rifles, holding trials for a potential replacement. Three of the finalists were the Heckler & Koch G36, SIG 500 series rifle and the Diemaco produced SFW (Special Forces Weapon). Because the British Army would not accept contractors who had been in bankruptcy within 10 years, Colt was disqualified from the trials. The winner was the Diemaco SFW. This was only the starting point. The weapon that would be supplied to the British Special Forces would be a highly customized and refined carbine.

Based on the accuracy requirement, it could not be made with a 14-1/2 inch barrel. In order to maintain accuracy, Diemaco produced a 15.8 inch heavy barrel. The barrel was heavy only between the chamber and front sight to provide a rigid mounting platform for add-ons and a greater heat sink for sustained firing. Furthermore, the heavy section and addition of a front barrel sleeve changed the vibration modes of the barrel when firing. Part of the requirement was light weight; however there was a trade off for accuracy that enabled the required accuracy to be met. There was another benefit: an increase in terminal performance over the 14-1/2 inch barrel. By increasing the velocity from 865m/s of the shorter barrel to the 895m/s of the SFW barrel there was an increase in penetration, range and terminal performance. The SFW were also equipped with a KAC RAS system.

Another modification was made based on the type of grenade launcher used. The British Special Forces use a Heckler & Koch grenade launcher that attaches to the bayonet lug. It was found that with use, the taper pins would either fall out or snap. When the front sight assembly was replaced, it would crack. Diemaco redesigned the front sight assembly to be made of a solid forging to increase the strength to deal with the grenade launcher.

This version has been sold in other configurations as well to other military and law enforcement customers. They may be found with standard handguards and standard front sight assemblies as well. An additional model is the SFSW (Special Forces Support Weapon) which has an even heavier barrel designed for the increased firing schedule. These come equipped with a RAS, vertical pistol grip, FAL-style carrying handle, bipod as well as a hydraulic rate reducing buffer (similar to that used in the LSW).

The C8CQB (Close Quarters Battle)

Many special operations units, both military and police, spend a lot of time in urban environments in close quarters scenarios. These include entries into buildings and caves which make longer barreled weapons clumsy and hard to move under cover and around corners. To answer this demand, Diemaco added another member to their C8 family of weapons, the C8CQB. This utilizes a 10 inch barrel with a Vortex flash suppressor. Other than the shorter barrel, it is identical to the rest of the C8 family of weapons. This is the only weapon that Diemaco puts in the rubber “D” ring extractor insert to increase extractor force to aid in reliability and may be equipped with a silencer (suppressor) as well. On these small entry guns the optic of choice is the reflex-type sights such as the Eotech holographic sight or the Trijicon ACOG reflex sight.

The C7 and C8 CT (Custom Tactical)

Many accurized versions of the AR-15/M16 weapon system are available at this time. The most notable being the Mk12 MOD 0/1 rifle in use by the United States Special Operations Command. Due to the inherent accuracy of this weapon system, it is possible with little effort to get a match grade barrel and have it shooting sub-moa at 100 meters. This degree of accuracy has both military and law enforcement applications. Diemaco produces two basic versions of accurized rifles/carbines.

The C7CT (Custom Tactical) is a highly modified C7A1. This rifle has a 20-inch heavy non-chrome lined, hammer forged barrel with an aluminum free floated barrel handguard. The barrel is designed to take a removable noise/flash suppressor very similar to that of the Mk12 MOD 0/1. To enhance accuracy, the rifle has a two stage trigger and titanium firing pin. The upper receiver has a flat top upper receiver with either a mil-std-1913 rail or the Canadian Weaver rail. Often the scope is attached to a Triad scope base to allow other devices to be attached. The buttstock is fitted with a removable weight to counter balance the additional weight of the heavy barrel. A bipod and sling swivels are also standard equipment. Additionally, a modified pistol grip is used to enhance performance. The maximum effective range with Canadian C77 ball ammunition is approximately 600 meters.

The C8CT is the carbine version which offers the same benefits but with a 16 inch barrel and a telescopic stock. The stock is modified with an adjustable butt pad. Due to the shorter barrel the maximum effective range is 400 meters.

Conclusions

Although not available in the United States, Diemaco produces one of the finest M16-type weapons in the world. What truly sets Diemaco aside from the rest of the manufacturers of this weapon is their diversity and ability to customize to the customers’ specifications. The weapons covered in these pages are but a small sample of what Diemaco produces. Many variations have been made at the request of their customers. Diemaco has taken the standard M16A2 and moved ahead with refinements and modifications of their own design.

Due to the Canadian Governments licensing agreement with Colt, the market place for Diemaco is limited. However, this is a company to be taken very seriously and if available to a customer, should be looked at very closely.

The author would like to thank Matt Kirkpatrick, Kelly Stumpf and Ian Anderson of Diemaco for their assistance with this series. Additionally, Mr. Andrew Weber of Armament Technology.