The Army and Marine Corps’ ongoing schism over standard issue 5.56mm ammunition came to a head during a recent House Armed Services Committee meeting. The USMC, which still uses the 1970s-era M855 round, supplemented by their Mk. 318 SOST ammunition, were a particular subject of contention:

U.S. lawmakers recently questioned Army andMarine Corps leaders on small-arms and why the two services buy completely different bullets for the M16A4 rifles and M4 carbines.

“You guys are using two different rounds, and you have procured several million rounds to date and you have used them in combat,” Rep. Loretta Sanchez, D-Calif., said at a March 19 House Armed Services Committee hearing.

Sanchez, the ranking member of the Subcommittee on Tactical Air and Land Forces, wanted to know why the Marine Corps uses the M855 5.56mm round and the Army uses the M855A1.

The services met with the subcommittee to discuss Fiscal 2016 modernization efforts — a touchy subject these days since the Pentagon is facing another round of mandatory budget cuts under sequestration in 2016.

“Maintaining two inventories of the same size combat ammunition is probably not the most efficient way to go,” Sanchez said.

“I just think it looks bad. It makes us all look bad. It appears very wasteful from the outside to have the Marines and the Army not buying the same bullet.”

But the Marine Corps and the Army’s decision to use two separate types of 5.56mm ammo is not a simple oversight.

The Army adopted the M855A1 in 2010 after years of struggling to find a lead-free replacement for the Cold-War era M855.

In recent years, troops also criticized the M855, saying it often delivered ineffective results on enemy behind battlefield barriers such as car windshields.

The M855A1 features a steel penetrator on top of a solid copper slug, making it is more dependable than the current M855, Army officials have maintained. It delivers consistent performance at all distances and performed better than the current-issue 7.62mm round against hardened steel targets in testing. It penetrated 3/8s-inch-thick steel at ranges approaching 400 meters, tripling the performance of the M855, Army officials said.

The Corps had planned to field the Army’s M855A1 until the program suffered a major setback in August 2009, when testing revealed that some of the bullets did not follow their trajectory or intended flight path.

We recently linked to an interview with Sal Fanelli, explaining some of the reasoning behind the USMC’s choice of the Mk. 318. The Mk. 318 can be seen as essentially the back half of a brass solid mated to the front half of an open tip match bullet. M855A1, on the other hand, is designed as a general-purpose cartridge, relying on the fragmentation of its jacket for terminal effect.

Representatives of the Marine Corps have stated on several occasions that they are interested in adopting the M855A1, pending testing. How this will turn out is anyone’s guess, but it’s clear that there is significant pressure to standardize with the US Army on ammunition.