To gain 40+ pounds, Bradley Cooper ate around 6,000 calories a day, which calculates to eating a meal every 55 minutes. Cooper added that it was not fun consuming those calories since his meals were usually in the form of bland protein shakes he had to choke down between weight lifting. Using his own trainer, he worked out four hours a day for several months. Cooper also took twice-daily lessons with a vocal coach, and spent many hours studying footage of Chris Kyle. When it came to pointing a rifle, Cooper trained with Navy S.E.A.L. sniper Kevin Lacz, who served with Kyle and was a consultant on this movie.
At his peak, Bradley Cooper could deadlift 425 pounds, twice his bodyweight, for five sets of ten reps each. Cooper said that during a workout scene in this movie, he was deadlifting 425 pounds, even though the filmmakers suggested he use dummy weights for the scene.
The real Chris Kyle once said that if there was a filmmaker that would make a movie about him, it would be Clint Eastwood, and no one else.
Kevin Lacz was also a U.S. Navy S.E.A.L. and served with Kyle, during which time he was given the nickname "Dauber". He was initially a consultant on this movie before Bradley Cooper offered him the chance to play himself in this movie, which he accepted.
Clint Eastwood: Early in the movie, Eastwood is seen with his back turned entering the church where Chris will steal his Bible.