Add a jarring blast of punk rock and cocaine to mountain music and you get Old Crow Medicine Show. Their first release, 2003’s “O.C.M.S.,” hit the bluegrass world like a freight train, and crashed through to let every other genre of music know something was going on. Bluegrass had long since ceded the spirit of the badass rambler to punk, rock, indie, even hip hop, but “O.C.M.S.” saw part of that spirit return home, changed through its pop culture journey but screaming through the fiddle like it always did.

“O.C.M.S.” was a tough act to follow. The album was popular partly because of its consistent attitude and honesty, but perhaps primarily because of its unstoppable southern anthem, “Wagon Wheel.” It brought the band appearances at venues from the Grand Ole Opry to Bonnaroo, alongside names like Del McCoury, Dolly Parton and Doc Watson, and made countless throats hoarse shouting “Rock me Mama like a Wagon Wheel.” Their second full-length release, “Big Iron World,” has no “Wagon Wheel,” but the album drives home their unique brand of unflinching aggressive bluegrass as well as anyone could ask.

“Big Iron World” opens with a bluesy drawl and a dobro slide. “Down Home Girl,” a classic ode to the farm girl, features a stripped-down guitar accompaniment that punches straight through the lazy dobro. Willie Watson sings over this slowly, angrily and with conviction. On “Don’t Ride that Horse,” a bluesy song that could have come off Bob Dylan and the Band’s “Basement Tapes,” Old Crow follows the newfound percussive leanings of their colleagues, Yonder Mountain String Band. Singer-songwriter Gillian Welch taps cool drums alongside smug vocals and a mean banjo to paint a picture of a smoke-filled room and a bitter old rounder.

While a song like “Down Home Girl” has mass appeal, the next two songs, “Cocaine Habit” and “Minglewood Blues,” pull no punches. Fast, loud and almost hokey, this is real bluegrass, and anyone not prepared to face mountain music head on should give up now. Once past this, though, the energy and drive of Old Crow’s up-tempo tracks are not to be missed. While these songs run the gambit from fiddle tunes, rags to gospel, the guitar slaps the downbeat with the same power across the board. The members of Old Crow mean what they say and do what they set out to do.

While “Big Iron World” explores new ground on tracks like “Don’t Ride that Horse,” it clearly has one foot stuck in “O.C.M.S.” “Cocaine Habit” is less of a new song than a sequel to “Tell it to Me” off of “O.C.M.S.” Same melody, same chord progression, same subject matter, same f-cking song. Funny, guys; please don’t do it again. “My Good Gal” has the same basic idea and structure as “We’re All in This Together,” as well as some of the same licks. Old Crow also certainly noted the success of “Wagon Wheel,” and that same swelling, epic sense is evident on many of these new songs, including “Don’t Ride That Horse,” “I Hear Them All” and “James River Blues.” The last of these three deserves special mention — it seems like Old Crow wants “James River Blues” to inherit the mantle of “Wagon Wheel.” A luddite wail, it takes on the tragedy of industrialization, fertile ground for some of the best folk songs ever written. Replete with howling fiddle and chilling mountain harmonies, the track hits right on the money.

“Big Iron World” was long anticipated after “O.C.M.S.” and it proves to be all a fan could ask for out of Old Crow’s second album. They show range within the repertoire of old-time, blues, gospel and folk, but never give up on their own mournful, strong and unique style. More serious than their partners in trendy bluegrass, Yonder Mountain String Band, Old Crow holds nothing back, and that conviction comes across in every one of their songs. In short, they are badass.