NATO Interoperability Trumps Advanced Firearms and Ammunition


The defense and sporting firearms communities are bombarded on a near daily basis with articles and advertisements promoting new “game changing” firearms and ammunition. Firearms manufacturers offer a number of “state-of-the-art” assault rifles and pistols that fire unique ammunition, claiming better range, superior lethality and improved reliability while exceeding the military’s current AR-platform systems, machine guns and service pistols that fire NATO-approved rounds. The question that follows in nearly everyone’s mind is why aren’t U.S. forces modernizing the military’s small arms arsenal with “game changing” 21st century weapons that shoot these new rounds?

The answer is neither complicated nor abstract, but it is an amalgam. It involves the North Atlantic Treaty Organization (NATO), United States law and several long-standing Department of Defense (DoD) Policy directives. And, all of these require U.S. forces to be interoperable with NATO coalition members. Perhaps a quick review of how we got here might be helpful.

Achieving Objectives

Consisting of 29 nations today, the NATO Alliance was founded in 1949 to counter the threat of Soviet invasion of Europe. Its focus was to stop a Soviet-armored advance across the European plains through combined retaliation from all 29 NATO member states. But getting 29 allied states to act coherently and effectively together to achieve tactical, operational and strategic objectives requires interoperability across numerous warfighting capacities, not simply small arms in the hands of determined soldiers.

Interoperability means forces and their warfighting systems must all mesh so they can operate together. In turn, this permits them to share common warfighting doctrines and procedures, each other’s infrastructures and bases and communicate using conjoint hardware and software. Interoperability reduces duplication by adding redundancy. Duplication, unto itself, always results in added cost, weight and convolution. Interoperability requires the pooling of resources, common training and leverages synergies between allied states. This, by all definitions, provides NATO a force multiplier and the robust military might necessary to defeat any adversary.


On the other hand, NATO interoperability does not necessarily require that member states purchase and use common brand military weapons and equipment. Rather, NATO places its importance on weapons that can fire common ammunition (more on this point in a moment), on forces and equipment that can share common facilities and on communications that can connect, interact and exchange data across the alliance. Recent NATO initiatives like “Smart Defense” and “Connected Forces” reflect NATO’s quest for interoperability and common connectivity.

Interoperability Required by Law

As previously stated, NATO interoperability is required under U.S. law, formal regulations and policy. For the Unites States, the Defense Cataloging & Standardization Act, Title 10, U.S. Code Chapter 145, Section 2451-2457 (Approved July 1, 1952) is the foundation. This law established a single, unified standardization program in the DoD. It requires standardization of items used throughout the DoD to the highest degree practicable and requires standardization and interoperability of equipment with North Atlantic Treaty Organization members and other U.S. allies.

Additional applicable U.S. law, regulations and DoD policy documents directing NATO interoperability are: Public Law 104-113, National Technology Transfer and Advancement Act, March 7, 1996; OMB Circular A-119, Federal Participation in the Development and Use of Voluntary Consensus Standards and in Conformity Assessment Activities; Federal Acquisition Regulation (FAR) paragraph 11.101(b) on Order of Precedence for Requirements Documents; CJCSI 2700.01, March 18, 2015,”Rationalization, Standardization, and Interoperability (RSI) Activities;” and DoDI 2010.06, July 29, 2009, “Materiel Interoperability and Standardization with Allies and Coalition Partners.”

Therefore, it is U.S. law and long-established policy that equipment procured for U.S. Forces employed in Europe under the terms of the NATO treaty be standardized and interoperable with equipment of other NATO members. Our policy further requires standardization of items and practices used throughout the DoD. Thus, interoperability between U.S. forces and coalition partners is permanent defense acquisition policy. Cost notwithstanding, this is why NATO dominantly plays into incorporating new small arms and ammunition into the U.S. inventory.

It Begins with Ammunition

Once all the law and policy documents are distilled, interoperability begins with ammunition. There are four approved NATO rounds: 9x19mm Parabellum, 5.56x45mm, 7.62x51mm and 12.7x99mm (.50 BMG), and none of these are commercial off-the-shelf ammunition. NATO ammunition performance is not measured the same as sporting ammunition. NATO ammunition must pass EPVAT testing. EPVAT stands for “Electronic Pressure Velocity and Action Time.” Action Time (in this context) means the (amount of) time required between the ignition of the primer and the projectile leaving the barrel. This is a comprehensive procedure for testing ammunition using state-of-the-art instruments and computers. The procedure, should you be interested, is described in NATO document AC/225 (Com. III/SC.1)D/200.

Unlike the Sporting Arms and Ammunition Manufacturers’ Institute’s (SAAMI) testing procedures used for the commercially available sporting ammunition market that primarily focuses on the shooter’s safety, NATO ammunition testing procedures not only includes the soldier’s safety but also a comprehensive functional quality testing in relation with the intended application (rifle, pistol, machine gun) and the capacity to incapacitate the enemy. As a result, every NATO ammunition order requires a complete acceptance testing and approval for both safety and functionality. This testing is performed by both NATO and the relevant ammunition manufacturers in a contradictory fashion. In order to accomplish this testing, a highly accurate and indisputable protocol has been defined by NATO experts using a system of reference cartridges.

The NATO reference cartridges system requires NATO’s ammunition manufacturers, under NATO’s watchful eye, to identify and set aside a batch (also termed “lot”) of ammunition they consider to be “of very good quality and representative of ammunition that should be delivered to the armies in the following years.” This batch is maintained at approved NATO test centers and distributed to the manufacturers involved as a test baseline. When a new batch (lot) of NATO ammunition is delivered, a set of 20 reference cartridges are fired, and this data baseline is compared to the performance of the new ammunition.

Each weapon and component considered vulnerable to the effects of a rapid change in pressure (for example, barrels, breech blocks and bolts) are tested by firing one dry round at a corrected minimum of 25% over pressure and one oiled round at a corrected minimum of 25% over pressure. Twenty-five percent over pressure means 25% in excess of the Service Pressure (Pmax). The Service Pressure is defined as the mean pressure generated by the Service Cartridge at a temperature of 21°C (70°F). This high pressure proofing is conducted with both the weapon and ammunition conditioned to an ambient temperature of 21°C (70°F).

Since NATO test centers only deal with the four (caliber) chamberings in military use, NATO EPVAT uses technically more stringent and different proof test standards than SAAMI and C.I.P. (with headquarters in Brussels, C.I.P. is the European equivalent of SAAMI and stands for Commission Internationale Permanente pour l’Epreuve des Armes à Feu Portatives). Therefore, EVPAT pressures cannot be directly compared with SAAMI and C.I.P. testing pressures. Correspondingly, SAAMI and C.I.P. proof houses test hundreds of different commercial (calibers) chamberings requiring a multitude of different test barrels and use less comprehensive test procedures than NATO.

Commercial and NATO Cartridges

With the above in mind, one might ask, for example, if the 7.62 NATO and the commercial .308 Winchester cartridges are the same thing. They are not identical, but they are similar enough that they can be loaded into rifles chambered for one another. The primary difference is that the commercially available .308 Winchester cartridges are typically loaded to higher pressures than 7.62 NATO cartridges. Even though SAAMI does not consider it unsafe to fire the commercial .308 round in weapons chambered for the NATO round, there is substantial debate about compatible chamber and muzzle pressures between the two cartridges. This debate is based on the differing powder loads and cartridge wall thicknesses of the NATO and commercial rounds. In the end, ATF recommends checking the firearm manufacturer’s stamping on the barrel that designates whether it’s designed for .308 or 7.62 NATO. The same is true for each of the other three NATO-approved rounds.

Why Only Four?

So how did NATO end up with only four approved cartridges—why not more? The short answer is that all 29 NATO nation members must unanimously approve any deletions or additions to the approved list. While it has been attempted, unanimous agreement to add additional rounds has proven impossible time and time again. There are politics involved that outplay performance and capability. Thus, the four approved NATO rounds will likely remain NATO legacy well into this century until replaced by caseless ammunition, man-portable directed energy weapons or something else soldier-carried not yet devised.

There is another huge motivation for NATO members to not deviate from the four approved calibers, and that is cost. As previously mentioned, as long as NATO members remain interoperable using the same ammunition, they can shoot it from any gun they wish. This means that many NATO members use assault rifles and machine guns they manufacture. The defense industry is big business, not just in the U.S., but in all nations that are capable of manufacturing military arms. These nations all use their own domestically manufactured military firearms.

In the case of the U.S. military, consider what it would mean to change the entire military’s assault rifle from the M16 (variants) to something different that shoots, say, 6.5mm Grendel (6.5x39mm), instead of the 5.56 NATO round. Let’s pretend that NATO approves and adds that round to the approved list. Let’s pretend that U.S. law and DoD policy are amended as well so this change can happen. Using the DoD as an example, here’s what the change would likely involve.

The entire U.S. defense force would need to be equipped with the new assault weapon. This means that all active-duty forces, reserve forces and National Guard would need new assault rifles. They would also require new machine guns / squad automatic weapons (light machine guns) that fire the 6.5 Grendel round. Our entire force would require training on the new weapons as would the armorers and the field and depot level maintainers. Stocks of 5.56 NATO ammo would need immediate replacement with the new 6.5 Grendel ammo.

Further, ample stocks of spare parts for all the new weapons would be required, and both these and the ammo would need to be immediately put into the DoD’s vast logistics supply system for worldwide supply to U.S. operating forces. As you might well conclude, this could only be accomplished with a major revamp of the logistics supply system; a problem of some immensity unto itself. How long might this change take? Years? And at what cost? And during the change, forces would obviously be using both 5.56 NATO and 6.5 Grendel along with the old and new weapons chambered for one or the other calibers exasperating an already stressed logistics supply system to get our troops exactly what they require.

The nightmare described above will also have to pass the litmus test of practicality. For example, if the 6.5 Grendel and its new assault rifle only provide, say, a 10% increase in reliability, lethality and hit probability over the M16-firing 5.56 NATO round, it would be a very hard sell (or a non-starter). While this may sound like a fictional scenario, it is a true reflection of budgeting and procurement reality. So, is a 10% increase in performance worth the trillion-dollar price tag? Most people would agree that it is not, and they would stick with the M16 and 5.56 NATO round.

Back to reality—since changing the NATO agreement, U.S. Law and engrained DoD policies requiring interoperability are, for all practical purposes, impossible (at least it is in this lifetime), the only workable and cost-effective option is to improve the existing ammunition, and that is exactly what NATO has done and continues to do. There are a multitude of NATO-approved 5.56 rounds available that offer heavier bullets with better weight-to-length profiles, more aerodynamic shapes (boat tails and ballistic points) and penetrator cores (light armor piercing), etc., etc.

Non-NATO Interoperable Weapons

NATO, law and policy restrictions do not apply to using non-NATO interoperable weapons and calibers for special purposes. SOCOM, for example, currently procures and uses special purpose weapons, and many of those weapons shoot exotic ammunition not available to other military units and definitely are not interoperable with conventional U.S. or NATO forces. But that is okay under the NATO agreement as well as U.S. law and policy; the key phrase being “special purpose use.”

Don’t Believe What You Read

So, the next time you read an article that announces the next best replacement assault rifle that shoots the next best ammunition that will replace the M16 and the 5.56 NATO round, remember that it won’t happen no matter how convincing it sounds. The rifle (bullet launcher) may change at great cost, but the ammunition it fires won’t without unanimous approval by all NATO members. Also, remember the overall replacement cost versus the improvement percentage in overall combat effectiveness is a major factor. If the delta isn’t overwhelmingly significant, it won’t be cost-effective, and it will fail.

Last, remember that most all of the articles about replacing one or more of the four NATO-approved rounds with something new and amazing is a product of shrewd advertising and defense industry promotion. The Program Executive Office–Soldier (PEO Soldier) is the DoD lead for soldier-carried weapons. PEO Soldier is always looking at new technology, but replacement of the military’s NATO interoperable calibers, or additions to them, is a non-starter.


  • Paul Evancoe

    Paul Evancoe is a freelance writer and author of numerous technical and political-military articles. He is the author of three novels: Own the Night, Violent Peace and Poison Promise available on-line at Amazon Books.