At the final phase, when you meet the Legion, side with them against the Van Graffs. The huge explosion will kill everyone inside. Do not search him and let him in - he is a suicide bomber. During your duty at the entrance, wait for the fourth customer.
Choose some badass gun and start the blood bath. Give away your weapons at the entrance and then obtain some high-tech weapons if you can pay for it. Notice however that everyone inside uses really newest technology when it comes to the weapons. Kill Simon (a bodyguard guarding the entrance), go inside the shop and start killing everyone. There are few ways to deal with Van Graffs. You have to kill all Van Graffs in Silver Rush. This quest can only be started after completing and if you have sided with Hardin and you've helped him to become Elder #1.
