In case you don't get this naturally, a very easy place to try is during the 11th mission Zero Hour.
You'll be tasked to defend against an APC, then a checkpoint. You'll need to fall back inside the perimeter and Find Ned. After rounding the corner, the objective will be Defend the trucks.
Directly in front of you is a blue shipping container. This opens and enemies come rushing out. Stand in front and chuck it towards the back when you see them. With any luck you'll nab 5. If you don't, restart checkpoint and you'll be really close.