Suited up in body armour and clutching a formidable assault rifle, Gerard Butler takes a break to chat with STACK on the Atlanta set of gritty crime thriller, Den of Thieves.

Portraying a member of an elite unit of the Los Angeles County Sheriff’s Dept (with Atlanta doubling for LA), Gerard Butler and his team are tasked with apprehending the state’s most successful bank robbery crew, who now have their sights set on the impenetrable Federal Reserve in downtown LA.

But there’s a thin line between the good and bad guys in this film and nobody is quite who they seem.

The directorial debut of screenwriter Christian Gudegast, whom Butler first met when he wrote the screenplay for London Has Fallen, the film also stars 50 Cent, Orange is the New Black’s Pablo Schreiber and O’Shea Jackson Jr., who made his impressive film debut portraying his dad Ice Cube in Straight Outta Compton.

“There’s two tribes in this movie, and both fall in close line on each side of the law,” explains Butler, no stranger to playing complicated heroes. “In a lot of ways our guys are no better than the bad guys in this film and, in some ways, their code of honour is stricter than ours.

“My character, Nick Flanagan, is a fantastic policeman, but he is very conflicted. He’s probably an addict, he parties way too much and has a very myopic view of this world where he lives for his work and the danger. For him it’s all about winning and being the alpha male, the top dog. He will do anything to get ahead.”

“In a lot of ways our guys are no better than the bad guys in this film”

50 Cent is chilling in his trailer when we meet him. Admittedly he’s not the most patient of actors.

“To me Hollywood is about ‘hurry up and wait‘. Hurry up and wait for someone to give you an opportunity to show how good you are. But I didn’t want to wait. I can’t actually wait. I’m busy. There’s sh-t to do,” says the rap icon who made his screen debut as an actor 13 years ago in Get Rich or Die Tryin’, a year later co-starring with Samuel L. Jackson and Jessica Biel in Home of the Brave.

He’s grateful he broke into acting after he became famous, rather than having to go out on auditions. “I got the luxury of being rich before this sh-t starts. I have to remind people, ‘You’re lucky I’m talking to you, motherf–ker. Get out of my face, alright?’ I need them to make appointments to talk to me. Call me tomorrow at 12, alright? Don’t talk to me right now,” says 50 Cent, who cites Robert De Niro and Al Pacino as his movie idols, co-starring with them in 2008’s Righteous Kill.

Born Curtis Jackson, he’s nonchalant about the ups and downs of his career, which involves various feuds, arrests and bankruptcies. “When I do something great they call me a ‘music mogul, entertainer’. I f–k up and they say ‘rapper 50 Cent’. You go right back to rapper.”

For Butler, one of the highlights of making Den of Thieves was an opportunity to visit the real Federal Reserve where billions of dollars are recycled every day. “There was one room that literally had trillions of dollars in there,” he says, eyes widening. “It was interesting to see all the safeguards in place, and even though they know we’re there making a movie, they never once let us out of their sight. So if our guide ever had to turn away, they had another guard behind us to make sure none of us were looking at the wrong things.”

And, of course Butler couldn’t resist taking a peek. “Listen, I’m a bad boy, I’m always going to look at the wrong things. I wanted to sneak away and go down a corridor. But it was just incredible to see the amount of money that’s destroyed every day, which is kind of what’s cool. Normally it’s about stealing money, but with this it’s like, ‘Let’s go and take the money that nobody’s going to use anyway’.”

Den of Thieves is in cinemas on February 1.