The STB 556 is one of the best Assault Rifles in Call Of Duty: Modern Warfare 3, known for its mid to long-range capabilities, low recoil and incredible accuracy. If you are after a reliable AR that has good all-around stats, the STB 556 is a great option.
To unlock the STB-556 in Modern Warfare 2, players just need to reach level 41 in their Military Ranks, which is done by just playing the game, using any weapons. From there, players level up the STB-556 to rank 21, unlocking a new attachment with each rank.