Den of Thieves director Christian Gudegast put the cast including Gerard Butler, Pablow Schreiber and 50 Cent, through a two-week training camp as prep for the film, which revolves around two rival groups -- The Outlaws (Schreiber's team) and The Regulators (Butler's team). 

To ensure authenticity, the actors trained in sync with their respective characters and teams. From using actual weapons to being trained by actual members of the forces, the cast did it all.

The Outlaws trained with Paul Maurice, who is currently on active duty with the US Armed Forces and who trains other service members in advanced tactical maneuvers and weaponry, read a statement.

"He gave the Outlaws tremendous confidence," Gudegast said. "They trained hard out on the firing range. They drilled in repetition until their movements with the firearms were completely fluid. They could load, unload, change 16 mags - the way they manipulated the firearms was just awesome, and that was Paul's doing."

The Regulators worked with Jay Dobyns, a retired undercover detective from the Los Angeles Police Department gang division. The group practiced techniques and tactics used by plain-clothes detectives, drilling down with great specificity.

The two groups used real weapons out in the field to get a feel for the heft and weight of the guns, and then practiced with paintball guns to get used to the mechanics of holding and shooting them while walking, running and jumping.

Schreiber said: "The Regulators would come to the training ground around the time we were leaving, or vice versa. We kept having these moments where we'd be passing each other and there was animosity and a lot of cold stares - as well as jokes thrown from long distance. It bred this healthy competition, which was good for Gerry and me to have because it bumped things up."

A crime saga set in LA, Den of Thieves follows the connected lives of an elite unit of the LA County Sheriff's department.