Any sufficiently heavy weapon (those with bipods or scopes, to be precise) will by default have a rather large AP cost to be shot with. To compensate for this, you need to take time to deploy your weapon.
- Deployment is performed by pressing the 'D' key. To draw a bead will cost a certain amount of AP, and it will reset if you move. After drawing a bead, the AP cost of your weapon will decrease and you'll be able to shoot much faster.
- If you carry a weapon that needs to be deployed, you'll see a symbol on your interface resembling a crosshair.