Borderlands 2: badass token challenge: shotgun sniper

Kill enemies from long range with a shotgun. Head to the vault of the warrior. Equip any shotgun with range, bullet spread, or scope. There are 3 Rakk spawning points; kill the Rakk until you get the one spawning to your right (it will spawn indefinitely from same spot). If you run out of ammo, go back to the vending machine by the quick travel to resupply. Rinse and repeat