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Now that's a title. It sounds like a lost Grindhouse trailer, or the great Neveldine/Taylor flick we’ll never have.

Some surprise is forgiven, then, when Machine Gun Preacher turns out not to be a beefy slab of exploitation but a furrowed-brow issue drama.

Gerard Butler plays real-life biker and bad apple Sam Childers, who stomps out of prison, raises hell for a while but then finds God, in a big way.

Only he’s not one for complacent Sunday pew-sitting, heading instead to war-struck Southern Sudan to build an orphanage – where his skills honed heisting dealers prove handy in fighting off predatory local warlords.

It’s quite a story, and you can’t help wondering what Paul Greengrass would’ve made of it. As it is, Marc Forster (Quantum Of Solace, Monster’s Ball) delivers something thoughtful and serviceable, without fully mining the drama’s potential depth.

Any film featuring not only profound and sudden religious conversion but brutal, knotty African conflicts demands sizeable guts to do them both justice. While Forster doesn’t shy from the cruelties of the Sudanese civil war, the complexities elude him somewhat.

Combatants are largely reduced to goodies and baddies, and a well-intentioned, well-made film wanders into the all-too-familiar white-guy-helpinghapless-Africans sub-genre.

Performances are solid, though, with Michael Shannon on reliably intense form as Childers’ troubled best friend and a focused Butler embracing his most imposing role since 300.

True, doubters may not undergo a radical change of heart, but it’s nice to see him flexing muscles other than his pecs.