The US Army Special Operations Command  (USASOC) 6.5 mm Precision Intermediate Calibre

Nicholas Drummond

For some time, the US Army’s Special Operations Command (USASOC) has been interested in intermediate calibres. Recognising the limitations of 5.56 mm ammunition, especially when fired from M4 Carbines with 14.5” barrels, it considered the .300 Blackout cartridge. This is very similar to the Russian 7.62×39 mm cartridge fired by the Kalashnikov assault rifle, but while it provides more consistent terminal effectiveness versus the standard M855 loading of 5.56 mm NATO, it did not increase engagement ranges. The wider re-adoption of 7.62 mm was not an ideal solution either, because of ammunition weight and recoil penalties. With much industry discussion of new calibres, USASOC believed it was worth investigating the potential benefits.

During 2017, USASOC conducted an evaluation of two intermediate caliber cartridges that could be adopted with only limited modifications to in-service 7.62 mm weapons. These were the 6.5 mm Creedmoor (CM) developed by Hornady and the .260 Remington. A comprehensive test programme included Doppler radar measurement to identify the best-best-performing projectiles, terminal effects evaluation, powder selection to ensure thermal stability, charge assessment, jump sensitivity, and other range testing to optimise the TDP. Four separate projectile weights were considered:

• 123 grains / 8.0 grams
• 130 grains / 8.4 grams (corresponds with current 7.62 mm M80A1 EPR)
• 140 grains / 9.0 grams
• 147 grains / 9.5 grams (corresponds with current 7.62 mm M80)

The final ammunition specification will be decided by the US Government before an RFQ is sent industry to manufacture production batches of the preferred ammunition type. Although no details have yet been made public, the US Army’s PM Soldier Weapons will have almost certainly supported this project with an EPR-style 6.5 mm bullet designed by RDECOM to allow the operational use of this calibre. We have already seen such a projectile developed for Textron’s 6.5 mm cased-telescoped ammunition system and it appears to have devastating potential.

Weapon reliability testing was conducted using modified 6.5 mm rifles based on the two sniper support weapons currently in US service: the FN Herstal FN SCAR Heavy Mk 20 Mod 0 Sniper Support Rifle; and the Knight’s Armament KAC M110 Semi-Automatic Sniper System (SASS). The Heckler & Koch H&K M110A1 Compact Semi-Automatic Sniper System (CSASS), which will soon enter service, was also evaluated. Two weapons of each type were used, one in .260 Remington and the other in 6.5mm Creedmoor and fired in comparison to existing 7.62 mm versions of the same rifles.

A third intermediate ammunition type could have additionally been tested, but wasn’t. This was the US Army Marksmanship Unit’s .264 USA cartridge. Instead of delivering a performance markedly superior to that of 7.62 mm, the US AMU round only matches it. Using extended 6.5 mm Grendel brass rather than a larger capacity case, the .264 USA lacks the extra long-range punch delivered by the more powerful rounds, but is usefully lighter.

USASOC’s test results showed that .260 Remington and 6.5 mm Creedmoor rounds comfortably outperformed the US Army’s existing 7.62 mm M118 sniper cartridge at long range (see table below).

In May 2018, USASOC announced that its preferred choice was the 6.5 mm CM and that it would adopt a further-developed version of this round as a Precision Intermediate Caliber. Though similar to .260 Remington, the 6.5 mm CM cartridge delivers comparable performance with lower recoil. It was also felt that the cartridge had a better growth path to accommodate potential future loadings. Versus legacy 7.62 mm ammunition, 6.5 mm CM ammunition was found to double hit probability at 1,000 metres; to provide a 33% increase in effective range; to deliver 30% increased energy on target; and decrease wind deflection by 40%. The other advantage of 6.5 mm CM is that it uses a necked-down version of the current 7.62 mm cartridge. This means it can be adopted in legacy 7.62 mm weapons with just a barrel change.

Anecdotal feedback about 6.5 mm CM performance has been overwhelmingly positive. Former-US Army paratrooper, Jim Schatz,* an architect of this initiative, advisor to SOCOM, and longtime advocate of intermediate calibres, described 6.5 mm CM as “a laser beam that was boringly accurate.” Industry insiders who have used this calibre confirm that its greater aerodynamic efficiency and superior ballistics correct everything that was ever wrong with 7.62 mm ammunition.

Earlier this year, it was also announced that USASOC would not only roll-out 6.5 mm CM in a long-range precision rifle, but would also use it in a carbine and assault machine gun. Unofficially, this suggests that the tests have exceeded expectations and that US Army Special Forces now intend to field their own new calibre long before the rest of the US Army and NATO does.

It can only be hoped that the British Army’s Infantry Trials & Development Unit (ITDU) will see fit to conduct its own intermediate calibre trial. It would take little to persuade LMT or Heckler & Koch to provide 6.5 mm CM versions of the L129A1 Sharpshooter rifle or HK417 / G28 DMR. Similarly, FN Herstal or Heckler & Koch would also supply a modified L7A2 GPMG or MG5 (HK121) machine guns, also in 6.5 mm CM. Perhaps UK Special Forces will also evaluate it?

It would be helpful if BAE Systems at Radway Green produced a 6.5 mm projectile along the same lines as those it developed for its excellent 5.56 mm and 7.62 mm EP enhanced performance rounds. This is because, so far, no European army has adopted US EPR projectiles due to concerns about whether they are compliant with the Laws of Armed Conflict. EPR bullets have an exposed steel tip for improved penetration and jacket is designed to rupture so that the bullet will fragment for improved lethality. Projectiles that fragment or deform are prohibited.

The importance of USASOC adopting 6.5 mm Creedmoor ammunition cannot be overestimated. First, it is a low-risk, low-cost approach to intermediate calibre validation. With the parent case based on a 7.62 mm cartridge, it is easy to implement and test versus legacy small arms systems. Second, it will provide a wealth of robust data including lethality and barrier penetration comparisons versus current NATO ammunition. It will provide an understanding of the logistical implications of adopting such a calibre, and an indication of whether a single intermediate round can replace both legacy 5.56 mm and 7.62 mm cartridges at section- and platoon-level. Third, it will allow polymer or alloy versions of standard brass cartridges to developed and tested. These offer a weight saving of 25-30% versus brass, with a starting weight of 20-22 grams for a brass 6.5 mm Creedmoor round, depending on the loading, final cartridge weight could be as little as 15-16 grams, which is only marginally heavier than 5.56 mm. Fourth, the US Army’s Next Generation Squad Weapons (NGSW) Program is extremely ambitious. Some would say that the requirements are unrealistic, if not unachievable. The 6.8 mm ammunition around which future weapons are to be designed are likely to generate much higher chamber pressures “to ensure that the rounds can still blast through enhanced enemy body armor at up to 600 metres.” Such performance is expected to be achieved by using pressures similar to those of a tank gun, i.e. up to 550 MPa (80,000 psi), instead of usual 5.56 mm pressures of 380 MPa (55,000 psi) for the M855 and 420 MPa (60,000 psi) for the M855A1. Based on current interpretations of the NGSW requirement, the US Army is looking for a weapon that’s considerably more powerful than 7.62 mm, with much greater recoil. While Textron’s Cased-Telescoped Small Arms System (CTSAS) looks promising, should it fail due to technical issues, due to cost, or for any other reason, then USASOC’s 6.5 mm PIC would provide a useful fallback capability, just as 5.56 mm did when the US Army’s SPIW project ran into technical difficulties in the early 1960s. Finally, 6.5 mm Creedmoor ammunition and weapons are likely to inform the NGSW effort by providing a useful technical benchmark for comparative evaluation.

There are a number of small arms professionals who believe that all efforts to develop a new intermediate calibre to replace 5.56 mm and 7.62 mm are futile. Their fundamental argument is that contemporary infantry rarely need to shoot beyond 300 metres. When they do, other more suitable support weapons are available, such as the 40 mm high velocity Automatic Grenade Launcher or 12.7 mm Heavy Machine Gun. Moreover, the number of occasions when 600-metre firefights take place, let alone 1,000-metre engagements, are likely to be few and far between. They also argue that if a 600-metre range requirement genuinely exists, then 5.56 mm ammunition could easily be developed further to achieve the required performance.

While the above points certainly merit consideration, those who advocate intermediate calibres would respond that the number of instances when a 600 to 1,000-metre range is needed is actually much greater than realised, because much of the previous analysis of combat engagements ignored the role of small arms in long-range suppression. While dismounted infantry units will usually have ready access to long-range support weapons, sometimes patrols will be isolated or surprised. When this happens, having the extra range capability that a more powerful organic weapon and ammunition type confer can be crucial.

The other important point to make is that any further development of 5.56 mm NATO ammunition is likely to require a longer cartridge with an increased capacity to give it more range and to contain a longer, more aerodynamic projectile. Thus a new 5.56 mm round is likely to be longer and heavier and require a new weapon with a longer action length. While this could be offset by the use of lightweight 5.56 mm cartridges, a polymer version of the 6.5 mm Creedmoor round would be so close to the weight of legacy brass 5.56 mm ammunition that the range and terminal effect gains make the marginal weight increase worthwhile. In particular, using 6.5 mm Creedmoor in a light machine gun instead of 7.62 mm would reduce the overall section/ squad weight burden as linked ammunition carried by every member carries a belt of 50-100 rounds.

Many of the arguments for and against an intermediate calibre are hypothetical. They need to be tested, which is exactly what USASOC’s 6.5 mm Precision Intermediate Cartridge will allow to happen. With hard evidence, NATO armies will be able to make robust future weapon and ammunition choices.

*(The late Jim Schatz was also a close personal friend and his loss last year was much mourned by the small arms community.)