The Counterpoise System consists of a new buffer assembly, drive spring and a counterweight which fits inside the bolt carrier of the rifle or carbine. It also includes a regulated gas tube for impulse adjustment and a "D" ring which installs beneath the extractor and eliminates M16/M4 extraction problems. The "D" ring also eliminates the requirement to change the M4 Carbine extractor every 2,000 rounds. The Counterpoise System eliminates muzzle rise and dramatically enhances practical accuracy in both fully automatic and semiautomatic fire by stretching the recoil impulse over the whole cycle time. Counterpoise also enhances reliability by adding more energy into the M4 operating system, thereby enabling the reciprocating parts to overcome the deleterious effects of dust, dirt and fouling. In addition, Counterpoise reduces the weapon's cyclic rate to 500-600 rounds per minute, thereby making the weapon far more controllable and accurate in fully automatic fire.


Counterpoise

A Major Improvement for M-16/AR-15 Rifles and Carbines

by Charles Q. Cutshaw

The American Heritage Dictionary defines counterpoise as: 1. A counterbalancing weight. 2. A force or influence that balances or equally counteracts another. 3. The state of being in equilibrium. We open this article with a dictionary definition because it helps to explain exactly how Counterpoise functions in AR-15 and M16 rifles. The Counterpoise system was designed by Jim Sullivan, Eugene Stoner's partner in the original AR-15 Project. Counterpoise development was accomplished as a joint effort by Sullivan and Mack Gwinn, who designed the FN Herstal quick-change barrel kit for the M2 Browning heavy machine gun. The impact of Counterpoise on the AR-15/M16 family of rifles and carbines will likely be far reaching. The simple Counterpoise system constitutes a major performance upgrade to the M16 family and improves the rifle's performance in the functional areas of accuracy, reliability and controllability.

In 2000, the M16 will become the longest serving Standard "A" military rifle in United States history, surpassing the 33-year record of the venerable M1903 Springfield that was officially replaced by the revered M1 Garand in 1936. There is no replacement rifle envisioned for the M16 and it will thus assuredly serve as the standard U.S. military rifle until at least the middle of the 21st Century, if not beyond. The much-touted Objective Individual Combat Weapon (OICW) will not replace the M16 as originally stated by the US Army. As matters now stand, the OICW will replace only army M16s that are equipped with M203 grenade launchers. The US Marine Corps has not yet committed to purchasing the OICW. Thus, the M16 is going to be with US military for many years to come. Despite modifications, however, the overall performance capabilities of the M16 have not truly been improved since the rifle was standardized in 1967. The M16A2, while arguably a product improvement, has always been somewhat controversial and did little to enhance the rifle's accuracy or reliability other than give it improved rear sights. Counterpoise is a natural product improvement to the M16 designed by a member of the team that originally developed the rifle. Counterpoise, unlike simple "one size fits all" rate reducers currently being marketed, addresses the weapon system as a whole and makes improvements in several areas. Counterpoise is currently undergoing evaluation by the special operations community for use in all their M4A1 carbines and if it proves successful there, it will almost certainly find its way into the American military's standard M16A2 rifles and ultimately into M16 rifles worldwide.

As stated, Counterpoise enhances the performance of the M16 in several areas. The rifle's accuracy is enhanced in both semiautomatic and fully automatic fire due to a significant reduction in the felt recoil impulse in both firing modes. The claimed reduction in perceived recoil impulse is approximately 50 per cent in semiautomatic and over 80 per cent in full automatic mode. The effect is most dramatic in full automatic where muzzle rise is virtually eliminated and an entire 30 round magazine can be emptied into a target at 50 meters by a trained shooter with almost every round falling into the center of mass of the target. In semiautomatic fire, follow up shots are much quicker because felt recoil is far less than with standard rifles and the shooter never loses his sight picture. "Double taps" can therefore be accomplished much more quickly with Counterpoise equipped semiautomatic AR-15 type rifles or carbines.

It is, of course, impossible to physically reduce recoil forces, but what can be done is modify them so that perceived recoil is reduced. Counterpoise achieves this by adding a three ounce (0.085kg) weight in the bolt carrier and by modifying the buffer. This dilates the recoil impulse a hundredfold, spreading it over the entire gun cycle time of approximately 1/10 second rather than the 1/1000 second internal ballistic cycle. Counterpoise is not "constant recoil," which would require even distribution of the recoil forces throughout the gun cycle. Constant recoil also requires open bolt firing which is not practical or acceptable in an assault rifle or carbine, especially on semiautomatic fire, where it degrades accuracy. What Counterpoise does in full automatic mode is use the rebounding weights in the buffer and bolt carrier to fragment the recoil spike and transmit some 80 per cent of it back into the weapon body via the operating spring acting over the entire operating cycle. The remaining 20 per cent of recoil force is divided into two 10 per cent spikes delivered half a cycle apart. One spike is delivered at the instant of firing and the other as the buffer impacts the rear wall of the recoil tube. The impact not only subtracts from the sharp force that occurs at the instant of firing, but allows Counterpoise to be used in any AR-15 type rifle or carbine without redesigning the firearm. Despite the fact that it is not truly "constant recoil," Counterpoise functions similarly in full automatic fire. Moreover, our testing revealed that the system actually does improve accuracy in semiautomatic fire.

Counterpoise enhances AR-15 reliability in two ways. First, a composite "D" ring is added beneath the rear of the extractor. The ring surrounds the extractor spring and progressively increases spring force fourfold, thereby solving the long-standing Ml 6 extraction problem, which was especially prevalent in full automatic firing mode. The second reliability enhancement is the addition of more energy into the overall operating system. Counterpoise not only replaces the buffer and recoil spring with improved components, but also adds an additional three ounces of reciprocating weight into the bolt carrier which functions as outlined above. The enhanced buffer also incorporates a rate reducer that lowers the M16's full automatic cyclic rate to approximately 550 rounds per minute. The addition of these enhanced components not only reduces recoil and improves accuracy, but also enables the rifle's reciprocating parts to overcome the effects of dust, dirt and fouling which may find their way into the receiver and operating parts. Conditions that would have previously caused a stoppage or use of the forward assist are eliminated when Counterpoise is installed.

At this point the reader may be saying to himself that Counterpoise sounds too good to be true, and the author must confess that he originally was skeptical. If it were not for Jim Sullivan's association with the project and Mack Gwinn's guarantee to replace or repair my Bushmaster XM15E2S carbine if the Counterpoise didn't perform as claimed, I would never have installed it. The required modification, while minor, is essentially irreversible unless one wishes to weld or replace his or her barrel. We have noted that Counterpoise incorporates more energy into the operating system by adding a heavier recoil spring, enhanced buffer and bolt carrier counter-weight. In order to operate these new components, more gas is required and the gas port must therefore be enlarged. This is not a project for the faint of heart - removing the gas block and then enlarging the gas port to accommodate an untried system is enough to give anyone pause.

However, we accomplished the deed without event and sure enough - it worked! Using my Colt HBAR Competition Sporter HBAR (AR-15A3) as control, we went to the range and found that the 6.3 lb (2.9kg) collapsible stock Bushmaster with Counterpoise was far more manageable than the 8.5 lb (3.8kg) full size Colt rifle, which has since received its own Counterpoise system. We were able to deliver semiautomatic fire so rapidly with the little carbine that it sounded almost like full auto! "Double taps" and accurate rapid semiautomatic fire are very easy with Counterpoise installed. The carbine's sharp recoil "spike" was reduced to a gentle push and we never lost our sight picture because the little rifle just stayed on target! The effect is most notable when one has both a Counterpoise-equipped rifle and a standard rifle available to make a side by side comparison. Since both rifles were semiautomatic only, we unable to test Counterpoise's full automatic capabilities until we gained access to a select fire automatic carbine belonging to a government agency.

We were given access to a select fire Colt M-4 carbine at a military installation near Washington, DC and found the effects of Counterpoise, as expected, to be more pronounced than in semiautomatic. As the military owners of the unfired M4 were understandably reluctant to allow us to enlarge the gas port of their carbine, we exchanged the M-4's upper receiver with ours and proceeded with our informal test. Felt recoil seemed little different than in semiautomatic, although an 80 per cent reduction is claimed. This is not to dispute the claim of the manufacturer, but simply that we could not feel a substantial difference between semiautomatic and full automatic recoil. Muzzle climb, however, was essentially eliminated and the cyclic rate was dramatically reduced. The M4 simply vibrated as we fired it and was much more controllable than without Counterpoise. Firing four to six round bursts, we kept all shots on a standard "E" silhouette target at 50 meters. We should note that burst control was greatly simplified by the carbine's slower 550 to 600 round per minute cyclic rate. As an aside, the reader should note that we do not like "burst fire" rifles that only are capable of firing in three round bursts without a true full automatic capability. While controlled burst fire is a key to accuracy in full automatic fire, the operator should be allowed to make the decision as to how many rounds to incorporate in his burst. Not only was burst control much easier, Counterpoise enabled the shooter to put virtually every round on target at 50 meters range. In short, the system performs as advertised in both semiautomatic and full automatic modes.

The M16 has been with the world's military forces for many years and will continue in service for many years to come. Counterpoise is arguably the most significant upgrade to the M16 since its standardization by the US military in 1967. Unlike competing "recoil reducers" and "rate reducers" being marketed, Counterpoise increases reliability and accuracy in both semiautomatic and automatic weapons. It is relatively inexpensive in that it costs little more than other designs that only reduce rate or recoil. Counterpoise can be installed by anyone who has any mechanical skills, although the manufacturer recommends gunsmith installation due to enlarging the gas port by drilling it out. In military use, Counterpoise should probably be installed by the support maintenance organization. We recommend Counterpoise to anyone owning an AR-15 rifle of any type, whether it is semiautomatic or select fire. Select fire users will derive the most benefits of the system, but Counterpoise also markedly improves the performance of semiautomatic firearrns. We have installed it in all four of our semiautomatic AR-type rifles and carbines, two of which are precision rifles for competition shooting. The implications of Counterpoise for military and law enforcement are obvious. Its effectiveness in close quarters battle scenarios where full automatic fire is the norm will enhance mission effectiveness. Moreover, Counterpoise enhances accuracy when the AR-15 is operated in semiautomatic mode. Counterpoise is currently being evaluated by both the US Army Marksmanship Unit and by special operations forces. If the system passes its testing and is adopted by the US military forces, we predict that it will find its way into millions of M16s and AR-15 rifles and carbines worldwide.

Finally, Jim Sullivan is not resting on his well-deserved laurels. Although we are not at liberty to give full details at the moment, Mr. Sullivan is working on several other M16-related projects. These include self-regulating gas tubes, quick-change barrels and other projects which will improve the basic M16 rifle and M4 carbine in ways that he and Eugene Stoner never dreamed of when they originally developed the rifle in the late 1950s and early 1960s. Although the M16 will be with the US military and many of the world's military forces for the foreseeable future, the genius of Jim Sullivan will continue to improve its performance and ultimately make it a very different rifle than the one he helped design so many years ago.

Initially published in the September 1999 edition of Small Arms Review

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