Sum 41

If Sum 41 sounds hardened on its fourth album, there’s good reason: The title refers to the name of a United Nations volunteer who helped the Canadian punk pranksters dodge bullets and explosions in the Congo, where the group was on a charity mission in 2003. The bandmembers haven’t totally lost their sense of humor — the video for the disc’s first single, “We’re All to Blame,” spoofs gyrating Solid Gold dancers — but spending time in the trenches certainly shook the mall-punk residue from their tunes.

Expounding upon the snarling metal fantasies of 2002’s “The Hell Song,” Chuck sounds battle-scarred. Jagged-lightning riffage and fret-shredding tempos dredge up the war-weary intensity of Black Sabbath or late-’80s Metallica (“The Bitter End”), while more punkish tunes (especially the no-brakes, Damned-esque “No Reason”) sound like a war zone. Vocalist Deryck Whibley’s nasally attempts at metal-dude gruffness backfire every so often — causing a few cuts to skulk like shady Linkin Park castoffs — but Chuck is both a loving homage to Sum 41’s headbanging heroes and an impressive progression.