Keep restarting the game til the Box is up at the lighthouse. Keep getting the box til you get the Scavenger.

Then get onto the island where the Quick Revive is, buy it, and unload your Scavenger on George. Make sure you leave a slow crawler.

George's hammer should spark, then spark purple, then flicker between orange and purple, then flicker orange. When you kill him you will get 2 Death Machines and a Perk (Stamina-Up, Speed Cola, JuggerNog, Quick Revive, Flopper Phd, or Daquiri Deadshot).

He will come back 2 rounds later. Get a Max Amo and unload the Scavenger on him again. He will then come back a 3rd time. Kill him again.

You will now officially kill him and get another achievement.