At the point where you find a grenade launcher after the telephone gets destroyed, find a cliff where you will get killed if you fall off. Lead an Agent to the cliff. Stand with your back to the cliff. Once the agent is at arms length away, Matrix jump over his head and run a short distance away. Then, turn around and take out the grenade launcher. Aim at his feet and try to blow him off the cliff, which saves ammunition. You can also try kicking him off.