The glib way to sum up Machine Gun Preacher is that it's a case of too much preaching and not enough machine guns. Marc Forster's film, as tone-deaf to American culture as his art-house hit Monster's Ball, has an interesting real-life story. Sam Childers (Gerard Butler) was a born-again former biker and petty criminal from Pennsylvania who decided to give up everything to help war refugees in Sudan. In Africa, he turned into a machine-gun carrying guerrilla to protect the orphans in his care from raiders, even though (as this movie claims, anyway) this obsession endangered his marriage.

Jason Keller's script reduces this unusual story to pure Chick-tract comic; Foster's action sequences are only slightly more legible than the edited-to-shreds stuff he did in Quantum of Solace. Glimmerings of the film's potential are visible from Michelle Monaghan, as his absurdly loyal wife, but the show here is stolen by Michael Shannon, in a preview of his startlingly fine acting in Take Shelter.

Shannon plays Sam's best bud Donnie—loose in tongue, wild in eyeballs and twitchy even in recovery. Shannon demonstrates the art of mush-mouthing dialogue that isn't worth enunciating. Sam hits bottom during a wild ride with Donnie, who is trying to shoot up a spoonful of something or other, even as he's driving through a winter night.

Compared to this diabolical inspiration, Childers' wrestling match with his God isn't as interesting—he's monotonous, from getting dunked at a brick church to rounding up orphans. The kids themselves are so indistinguishable to Forster's camera that one of them has to be scar-faced and mute so we can tell him from the rest. In all, the film doesn't seriously consider the Christian duty to turn the other cheek, and it doesn't fulfill its duty to its grindhouse title, either.

'Machine Gun Preacher' plays through Oct. 13 at Century Northgate 15. 7000 Northgate Drive, San Rafael. 415.491.1314.

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