World War Z

You can easily grind this on Episode 1 New York, Chapter 3: Hell and High Water . As soon as you start the level, exit the train station area down onto the street. You'll have to clear out a few zombies. Once the streets are clear, flank to your left, near the end of the street next to a white car you'll see a breaching charge that will ALWAYS spawn there every time you play this chapter. Once you picked up the charge, continue through the level until you get to the first ammo supply section. To the left of the ammo supply is the breach charge door. Simply place the charge on the door, and boom, that's one out of 15 done. Simply quit and restart, and grind that 14 more times

On Episode 1 New York, Chapter 3 Hell or High Water the breaching charges spawn In the same places through out the level.

I played on easy with the AI. This level works well if you are going for the achievements for Building Defenses(Builder), Disarming Mines(waste of time) and Disarming Turrets(Friend of machines) there are only 2 turrets but as you are going to get 3 breaching charges a run as well as xp for finishing the level personally I found it worth it.

Also if you havent got the achievement What the doctor ordered. You can do using friendly fire on the AI (level 3 weapons are quickest) get the AI health down into the final health box I always kept shooting till there was only a sliver of health. There are tonnes of med kits at ammo stations on easy. Rinse and repeat.

The breach charges are located as follow.

Charge 1: as you leave train station head down the left and you will find the charge next a white car at the back on the left side.

Breach Door 1: As you continue you'll reach an ammo box and its directly in front of you.

Charge 2: You will have to drop down beneath a train in the repair yard. As you follow the tunnel round you will get the way point to climb up. Before you do on the left there will be a tunnel if you go left it will take you back round to the start. If you go right the charge will be on the floor on the right.

Charge 3: This one you wont becable to collect of playing solo. But if playing with a mate it would mean you will both be able to pick up 2 charges each per run. After climbing up the train you will then gave to drop down onto a train to continue. Keep left on the walkway. Climb the box and carry onto the end and the charge will be in front.

Breach Door 2: After collecting charge 3 you will follow waypoint and drop down off train. The door will be in front off you on left hand wall.

Breach Door 3: Head straight from previous Breach Door you'll get to a dead end. On the right will be a cargo container with a breaching door.

Charge 4: When you reach final area with boat you will begin setting up defences. As you enter the area the ammo station will be in front to your left to the right theres a set of stairs. Between these areas walk way which leads you to a cargo container with a breaching door(Door 4). Look past the door to the left on the lower platform and you'll see some boxes. The charge is behind the boxes.

Breach Door 4&5: Door 4 is mentioned above.

When entering the area the ammo station is directly in front of you. Do a 180° turn and Door 5 is behind you.