Being around the sights and sounds of battle brought back the memories of his deployment to Iraq with SEAL Team 3, one of the elite units that make up the US military special forces.
Lacz trained Cooper on how to hold and shoot the various weapons that Kyle utilized.
Cooper never equaled the shot from 2,100 yards Kyle once made in Iraq, but he was able to hit targets from 600 yards.
But before he could slip into the role of the one-man killing machine in Clint Eastwood's film, Cooper had to learn how to shoot a sniper rifle.
And for that expertise he turned to one of Kyle's close friends, former Navy SEAL sniper Kevin Lacz who served two tours of duty.
'When he was kitted out in the full combat gear he could easily have passed for Chris.
'It was just amazing to watch him transform into the character.
Such was Kyle's skill as a sniper he was credited by US military chiefs with 160 confirmed kills.
One of his most spectacular shots was killing a man armed with a rocket launcher from a distance of 2,100 yards.
Cooper went on a 5,000 a day diet to bulk up his weight so he was the same size as Kyle.
He never met Kyle in person but spoke to him on the phone.
Around him were burnt out buildings, spent bullet casings and the sound of grenades exploding.