Earn the Combat Engineer pin 100 times (worked on 5 fortifications in one deployment in Horde)
Infinite ammo for all weapons.
Method: Horde Private. Put difficulty on Hardcore or Insane. Wave start at 1. Then Have a second controller give you their cash so you have 2000. Build a base. Then a turret. Get on the turret Fire a few shots. Get off and repair
it. Repeat till you have the medal. Then die. Rinse and repeat.