First find the size of the second bell: 50 pounds * 2 = <<50*2=100>>100 pounds
Then find the size of the third bell: 100 pounds * 4 = <<100*4=400>>400 pounds
Then add the amount of bronze used for each bell to find the total: 100 pounds + 400 pounds + 50 pounds = <<100+400+50=550>>550 pounds
#### 550