The United States House of Representatives has ordered trials to be conducted to determine the right ammunition for both the US Army and Marine Corps, following on the recent controversy that each service was using its own unique round. Army Times reports:

The Army and Marine Corps will conduct comprehensive testing this year to determine the viability of adopting common rifle ammunition, a potential cost-cutting initiative that could have serious implications for troops on the battlefield. Members of Congress are driving the efforts, saying the switch to a single 5.56mm cartridge for all conventional U.S. forces stands to save American taxpayers considerable expense. It is likely to prompt a showdown between the two rounds favored by each service, raising the possibility the Marine Corps could be forced to adopt ammunition it rejected in 2009 because its early development was plagued by problems. On capitol Hill, the House Armed Services’ Subcommittee on Tactical Air and Land Forces has ordered Defense Secretary Ashton Carter to study the issue and report to Congress by next March whether it still makes sense for the Army to use its M855A1 round while the Marine Corps moves to make the M318 Mod 0 Special Operations Science and Technology round its new standard. “The Army and Marine Corps are using a very similar enhanced small caliber 5.56 rounds for the same operational environment,” subcommittee chairman Rep. Mike Turner, a Republican from Ohio, told Marine Corps Times April 29. “We want to ensure our warfighters are provided with the best equipment available and ensure maximum value to the taxpayer.” The subcommittee’s ranking Democrat, Rep. Loretta Sanchez of California, has indicated she also supported the potential shift. Concerns with the Army’s round Marine Corps officials say they do not oppose the idea, provided the Army has fixed its round’s propensity to wreak havoc by causing excessive wear on a weapon’s inner workings. The problem stemmed from the M855A1’s high chamber pressure and exposed steel tip, which could chew up a weapon’s feed-ramp, erode barrels and crack bolts, said Col. Michael Manning, the program manager for Infantry Weapons Systems at Marine Corps Systems Command in Quantico, Virginia. The Marine Corps believes SOST is superior “at this time,” he added, “but we are always open to testing and are participating in ongoing testing of the M855A1. We will always adopt whatever is best for the service.”

While the projectile design of the M855A1 in my opinion provides superior general purpose capabilities to the Mk 318 round, the concerns about its wear characteristics are very real. The round has proven to erode the aluminum feed ramp extensions that are integral to the upper receiver after tens of thousands of rounds, leading to an earlier retirement of rifle upper receivers than the previous M855 round. The Army is seeking to fix this problem with new magazines that will present the ammunition at a positive angle so that the rounds never contact the feed ramp extensions, but it’s unclear if the USMC has been given any of the new magazines for testing, or if they are amenable to the idea of adopting a new type of magazine jointly with the Army.

Other concerns of wearing out bolts and barrels more quickly are also relevant, but the reduction in life of these parts is not as great as the upper.

I would be very surprised if these trials determine that the Army and Marine Corps cannot field a unified rifle round. I suspect the most likely result will be the armed forces-wide adoption of the M855A1 round, possibly with the new improved magazine in tow, as this would likely reduce costs the most.