Gritty, gory and violent, “Machine Gun Preacher” is a better action picture than it is an uplifting story about a violent man who found religion and a cause and became better for it.

Because that, this Marc Forster film suggests, just isn’t what happened. This confused and unsatisfying “true story” has a solid, tormented lead performance by Gerard Butler and promises the arc of a tale of redemption. But in missionary-with-a-machine-gun Sam Childers, the movie has a hero it cannot make its mind up about. And that confusion muddles the movie.

We meet Childers (Butler) the day he gets out of the joint. A violent, drug-dealing biker, he has enthusiastic sex with his wife (Michelle Monaghan) in her tiny Ford Pinto, settles back into their trailer and picks up right where he left off before prison. He drinks. He fights. He takes drugs. And he robs others who have the drugs.

Michael Shannon is wonderfully cast as his biker-junkie running mate.

Sam’s wife used to strip, and he’s none too pleased when she tells him why she quit.

“It ain’t right in the eyes of God.”

But Sam eventually crosses his own line and snaps. That’s when he, too, finds religion, gets his life straight and eventually starts his own church in rural Pennsylvania. And that’s when he becomes aware of the situation in Sudan and Northern Uganda, where warring groups torture, rape and kill adults and kidnap kids to be in their armies.

Sam, now a Man of God, tries to do things the turn the other cheek way. But for a man with his access to guns and knowledge of them, there’s only so many kids he’s going to watch carried off, only so many times he’ll stand by and watch his new orphanage  burned down. As he tells a rebel soldier who asks him if he’s in the military, “I just like my guns.”

Butler brings a wild-eyed bravado to this real-life character, suggesting a conflicted, blood-stained man who seeks redemption by spilling more blood. You can believe this guy as both a preacher and a can-do biker not afraid to pull the trigger.

“God don’t only call the good,” he says. “I reckon he calls us sinners, every now and then, too.”

But Forster (“Monster’s Ball,” “Kite Runner,” “Quantum of Solace”), working from a Jason Keller script, has made a film that is all over the place and often over-the-top. See Sam shotgun his way out of a tornado. See his fury at being unable to persuade rich townsfolk from pitching in on his cause. See him make terrible life-or-death decisions (a few of which seemed to have easier solutions than the film presents) involving the legions of kids he is obsessed with saving.

The confusing politics of that corner of Africa don’t help.

“Machine Gun Preacher” quickly descends into something far more conventional than a tale of redemption. It becomes a revenge fantasy, one bathed in gore, in which Forster unblinkingly shows the violence visited against these children as a way of saying that Childers’ ends justify the means.

But the movie never convinces us that Forster is convinced himself. The director lines up this bad good man in his sights, but he never quite has the nerve quite to pull the trigger.

“Machine Gun Preacher” opens in Orlando Friday. Here’s my piece on the real Machine Gun Preacher, and director Marc Forster’s take on him.

MPAA Rating: R for violent content including disturbing images, language, some drug use and a scene of sexuality

Cast: Gerard Butler, Michelle Monaghan, Michael Shannon, Kathy Baker

Credits: Directed by Marc Forster, written by Jason Keller, based on “Another Man’s War,” by Sam Childers. A Relativity Media release.  Running time: 2:07