The M-16s and M-4s carried by the United States armed forces use the 5.56×45mm cartridge. NATO STANAG 4172 provides a standard for all NATO forces. Even though they meet the same standard, the US Army and the US Marines have different ammunition.
The Americans adopted the 5.56×45mm NATO SS109 cartridge (U.S.: M855) cartridge in the 1980’s with the M-16A2 whos 1:7 twist rifling was well suited for the heavy bullet. The M-885s 62 grain projectiles have a lead core bullet with concentric steel penetrator. M-855 should penetrate approximately 15 to 20 inches into soft tissue under ideal circumstances. This sounds good, but if your target is less than 15 inches thick, you will most likely have no yaw or expansion.
There were widespread reports of inadequate incapacitation during combat operations after multiple hits by M-855 ammunition. The bullets tended to exit the body of the enemy soldier without yawing and fragmenting. This lack of expansion provides better penetration of light cover such as walls, wood, and vehicles.
The 5.56×45mm M-855 cartridge was designed for maximum performance when fired from a 20 inch barrel, as was the original 5.56 mm M-193 cartridge. Many complaints can be attributed to the 14.5 inch barrel length of the M-4 carbine which generates less muzzle velocity than the longer 20-inch barrel found on the M-16 rifle, and terminal performance can be a particular problem with the M-4.
The Marine Corps, until recently, stayed with the M-16A2 and still uses an M-855 round. The Army widely adopted the M4 Carbine and now uses the “improved” M-855A1. The Army claims that the M-855A1 steel-and-copper round performs better.
The Fiscal 2017 National Defense Appropriations Act, which looks fairly certain to pass, includes a provision requiring the secretary of defense to submit a report to the House and Senate Armed Services Committees explaining two services are using different types of 5.56 mm ammunition for their rifles. The report must be submitted within 180 days after the bill, which includes the entire defense budget for the coming year, is enacted.
Unless the Secretary of Defense declares an “emergency” , the Army and Marine Corps must adopt a standard round within a year after the bill is passed.
The Marine Corps Systems Command, told congress there were plans to test the M855A1 rounds. Let’s hope they perform well and we get great ammo for the troops.
Photo courtesy of US Marine Corps