The USMC has started to use a new round in Afghanistan. The new "Special Operations Science and Technology" (SOST) 5.56 round, also known as the "MK 318 mod 0" is being billed as being more accurate and granting more lethality and range than the standard M855 round. Supposedly, the new projectile is better able to perforate barriers than the M855. The M855 uses a 62 grain green tip (in order to differentiate it from M193 and other rounds) projectile with a steel penetrator, and is known as the "SS109".
Congress had to approve the new projectile for use by the military due to it's unique open tip design. It seems to be borrowing some attributes from the MK262 round employed by the US Military and the Tactical Bonded and Trophy Bonded Bear Claw projectiles made by Federal. It also is a 62 grain projectile, like the SS109.
The Director of the Navy Department International and Operational Law Division, J.R. Crisfield wrote, "Based on the significantly improved performance of the MK318 MOD 0 over the M855 against virtually every anticipated target array in Afghanistan and similar combat environments where increased accuracy, better effects behind automobile glass and doors, consistent terminal performance and reduced muzzle flash are critical to mission accomplishment, USMC would treat the MK318 MOD 0 as its new 5.56mm standard issue cartridge"
It was originally designed for SOCOM to be a better round in shorter barreled weapons such as the SCAR. However, it had some obvious appeal for the USMC. Keep in mind, it will not be replacing the M855, but complementing it.
The MK318 MOD 0 is more expensive than the standard M855 round, but the USMC is hoping that the price will decrease once it is in greater production.
I am very interested in hearing about how this round performs in the field because it appears to be a winner.