Give Lady Antebellum credit: There’s a consistency to its songs that makes the group as much a manufacturing concern as it is a country act. But that also means that five albums in, the once-reliable formula has become threadbare through overuse. Whatever chemistry singers Charles Kelley and Hillary Scott had fizzles on “747“; they may share “One Great Mystery,” “Lie With Me,” and joint reminiscence “Damn You Seventeen,” but they’re only taking turns talking, not creating a dialogue. (They do better individually on Scott’s sunny “Down South” and Kelley’s regretful title track.) With a minor-key, dulcimer-enhanced English folk-ballad melody completely at odds with a lyric that could hardly be happier, “Long Stretch of Love” is a jumble of ill-fitting parts all cranked up to arena volume, and the welcome friskiness of “Freestyle” is undercut by the inanity of what Kelley’s singing. “747” also suffers from baffling sequencing, opening with three downbeat songs and closing with the train-track skip of kiss-off “Just a Girl,” a song with so much modesty and so little finality to it that the record seems to simply stop. (Out Tuesday)