BY TOM ROEDER tom.roeder@gazette.com -PUEBLO - The beginning of the end came with a heavily muffled bang."It's more a whumph," said Pueblo Chemical Depot worker Jonathan Miller, who helped set off the explosive charge last week to destroy the first three shells of what will be a multi-year effort to rid Colorado of nearly 800,000 mustard gas rounds.The lack of a big bang, though, didn't disappoint.