His easygoing grooves and relaxed voice make Riley Etheridge Jr. an exemplary Americana artist, but the South Carolina native is a musician who slips past the genre altogether. On this year’s full-length Powder Keg, Etheridge uses such first-rate sidemen as harmonica player Mickey Raphael to construct a genial but far from uncomplicated record that goes from country to pop and R&B. “Nobody’s Hero” is a gorgeous bit of country, while the title track updates Southern rock. Powder Keg is a worthy follow-up to Etheridge’s 2009 release Things I Used to Know, which sported the country-power-pop tune “He Said, She Said” and the unclassifiable “Brand New Neighbors” — a song about Etheridge’s move to New York City. “About 8 million people welcome me when I come home,” he sang in “Neighbors.” Etheridge is a genuinely charming artist whose skill equals his unerring sense of self.