How do you unlock the USAS-12 in Battlefield 3

In Battlefield 3 online multiplayer, the player can unlock weapons by gaining points. The "USAS-12" shotgun is unlocked by reaching rank 43. To rank up the player must gain enough points to reach the next rank with each successive rank requiring more point to reach. Some ways of gaining points include:

• Killing an enemy (100)
• Capturing a flag (250)
• Healing, repair and rearming friendlies (20, 10, 10)
• Disabling and destroying enemy vehicles (100, 50)