The 5.56x45mm NATO Debate Comes Back: M855A1 vs. MK 318 SOST

A long standing divide between the Army and the Marine corps over what ammo type to field is coming up once again. The congress critters on the House and Senate Armed Services Committees are asking the Secretary of Defense to submit a report on why the two military branches are using different types of 5.56x45mm NATO. reports that if the current bill passes and is signed by the president the Secretary of Defense will have 180 days to explain to congress why the Marines and the Army are fileding these two types of ammo instead of using just one type across both branches.

This issue has come up in the past and actually has a long history, with multiple interests coming into conflict over what 5.56 NATO round the military will use.

The History of the Divide

The M855A1 is at the heart of this divide
The M855A1 is at the heart of this divide

To briefly summarize the history that has brought us to the current situation. During the Cold War the standard 5.56 round was the M855. This round used a lead core with a steel tip and a copper jacket and remained the standard round used by US forces until 2010 when the improved M855A1 cartridge was adopted. The M855A1 retained the steel penetrator tip, but initially used a bismuth-tin alloy core. Later versions of the M855A1, know as the M855A1 EPR would replace this core with a copper core, eliminating the issues that were seen with the previous design.

In 2009 testing showed that heat could adversely affect the accuracy of the new design. Furthermore the M855A1 faced criticism over its “environmentally” friendly design. Many opponents worried that the military was more worried about “toxins” in the ammo then the actual effectiveness of the round. Because of the testing issues found with the initial design of the core for the M855A1 the Marines started to look at other options.

While the issues with the M855A1 were ironed out, the Marines continued looking and eventually settled on a different design. The MK 318 SOST. While it was supposed to be an interim round, while the issues with the M855A1 were ironed out, the Marines ended up sticking with the MK 318 SOST round. Developed by the U.S. Special Operations Command, the MK 318 SOST round uses a open-tip, match round design, over a lead core, common with sniper rounds. The Marines were supposed to test the improved, copper core, M855A1 round back in 2010, but apparently never did. Testing was supposed to happen again in 2015, but again data, on these tests seems to not be publicly available.

This has led to the current situation that we have. Two major branches of the armed forces using different standard cartridges.

A Very Unusual Situation

soldierSince the start of the 20th century our military has standardized around a single cartridge for basic deployment. But since the split in 2010 over the issues with the M855A1’s design the Army and the Marines have been using different types of ammo. Something that had not happened for over a century.

Unless the Secretary of Defense determines that there is an “emergency” reason for the branches to continue using two separate types of 5.56 ammo, they will have one year to settle on a single round for both branches.

At the end of the day, it comes down to this, what’s the most effective round for our troops to use. Our military should be using the best rounds available to them and not be tied up over petty concerns about “lead free” bullets. However the debate continues as to the effectiveness of these various types of 5.56 NATO cartridges.

Let us know what you think about these recent developments in the comments below.