All weapons:
In the middle of gameplay in the campaign mode hold the left and right bumper buttons and press Right, Right, Down, Up, Left, Left on the D-Pad.

Achievements:
Complete each achievement to get the allotted gamerscore. For achievements that say campaign, do them in campaign mode. For achievements that say online, do them online:

Expert Sniper: Campaign (25):
Kill 10 enemies using Sniper Kit weapons without losing the multiplier.

Expert Assault: Campaign (25):
Kill 10 enemies using Assault Kit weapons without losing the multiplier.

Navy Cross: Campaign (20):
Kill 5 enemies using water based vehicles without losing the multiplier.

Medic: Campaign (20):
Heal 4 allies without dying using the Auto Injector, at least 1/3rd health must be restored.

Mechanic: Campaign (20):
Repair 5 allied vehicles in a mission using the Blowtorch, at least 1/3rd armour must be repaired.

Marksman: Campaign (20):
Kill 4 enemies with one clip of a sniper rifle.

Air Force Cross: Campaign (20):
Kill 10 enemies using air based vehicles without losing the multiplier.

Army Cross: Campaign (20):
Kill 10 enemies using land based vehicles without losing the multiplier.

Dominator (20):
Finish top in 20 games.

Conqueror (5):
Finish top in 5 games.

Coalition (50):
Complete 50 major victories.

Alliance (20):
Complete 20 major victories.

Expert Special Ops: Campaign (25):
Kill 10 enemies using Special Ops Kit weapons without losing the multiplier.

Expert Support: Campaign (25):
Kill 10 enemies using Support Kit weapons without losing the multiplier.

Grenadier: Campaign (20):
Kill 20 enemies with grenades in a single mission.

Expert Engineer: Campaign (25):
Kill 10 enemies using Engineer Kit weapons without losing the multiplier.

Commando: Campaign (20):
Kill 4 enemies in a mission using a Knife.

Sapper: Campaign (20):
Kill 20 enemies using C4 or Landmines in a single mission.

Expert Use of Mortar: Campaign (20):
Kill 3 enemies and no allies with a single Mortar Strike.

Army Cross: Online (20):
Kill 10 enemies without dying using land based vehicles.

Air Force Cross: Online (20):
Kill 10 enemies without dying using air based vehicles.

Marksman: Online (20):
Kill 4 enemies with one clip of a sniper rifle.

Medic: Online (20):
Heal 4 allies without dying using the Auto Injector, at least 1/3rd health must be restored.

Navy Cross: Online (20):
Kill 5 enemies without dying using water based vehicles.

Mechanic: Online (20):
Repair 5 allied vehicles without dying using the Blowtorch, at least 1/3rd armour must be repaired.

Expert Assault: Online (25):
Kill 10 enemies without dying using Assault Kit weapons.

Expert Sniper: Online (25):
Kill 10 enemies without dying using Sniper Kit weapons.

Expert Special Ops: Online (25):
Kill 10 enemies without dying using Special Ops Kit weapons.

Expert Engineer: Online (25):
Kill 10 enemies without dying using Engineer Kit weapons.

Expert Support: Online (25):
Kill 10 enemies without dying using Support Kit weapons.

Grenadier: Online (20):
Kill 20 enemies with grenades in a single round.

Commando: Online (20):
Kill 4 enemies without dying using a Knife.

Sapper: Online (20):
Kill 20 enemies using C4 or Landmines in a single round.

Expert Use of Mortar: Online (20):
Kill 5 enemies and no allies with a single Mortar Strike.

Almaty Veteran (5):
Complete all missions in the Almaty region.

Mangystau Veteran (10):
Complete all missions in the Mangystau region.

Qyzylorda Veteran (25):
Complete all missions in the Qyzylorda region.

Admirable (5):
Achieve the maximum star rating in 5 missions or challenges.

Meritorious (20):
Achieve the maximum star rating in 20 missions or challenges.

Exemplary (50):
Achieve the maximum star rating in all missions and challenges.

Victorious China (30):
Complete all China missions.

Victorious NATO (30):
Complete all NATO missions.

Practiced (5):
Participate in 50 game sessions.

Seasoned (20):
Participate in 200 game sessions.

Veteran (50):
Participate in 500 game sessions.

Team (5):
Complete 5 major victories.