Risky venture (6)
(Other definitions for gamble that I've seen before include "Bet -- Procter's partner" , "Take risks" , "Wager; sounds like frolic" , "Place bets" , "Take a chance, speculate" .)
(Other definitions for long shot that I've seen before include "Outside chance" , "An undertaking with little chance of success" , "Very chancy venture" , "filmed at a distance" , "Unlikely winner" .)