5 Seconds of Summer Billboard Cover 2014

Calum Hood, Michael Clifford, Luke Hemmings and Ashton Irwin of 5 Seconds of Summer photographed on June 29, 2014 at the Radisson Blu Hotel in Milan by Miller Mobley.Miller Mobley

5 Seconds of Summer couldn't have asked for a more perfect few days. The Australian pop-punk quartet is atop the Billboard 200 this week with the chart's third-largest opening of the year, and on Thursday they premiered the video for their latest single, "Amnesia." Add a newly announced concert tour for 2015 and you could say things are looking good for Luke Hemmings, Michael Clifford, Calum Hood and Ashton Irwin.

In this week's Billboard, the guys open up about their DIY beginnings back in Sydney, the success of "She Looks So Perfect," and the backlash they've been getting from pop-punk purists. "We're so proud of the music we make -- we love it -- and we’re fearless," says Irwin. "If anyone puts us down, we don’t care. Isn't that somewhat punk -- not giving a damn what people say?"

We'll unleash the full cover story on Monday morning, but till then check out five things we learned about the fun-loving foursome.

IT ALL BEGAN WITH A DECENT PROPOSAL. After Hemmings snagged a "few views" for his 2011 YouTube cover of Mike Posner's "Please Don't Go," his school chum Clifford approached with a simple best proposition. Hemmings recalls: "He came up to me at school and said, 'Do you want to do one together and, like, maybe make a band or something?'"

5 Seconds of Summer: The Billboard Cover Photo Shoot

NO FREE SKIVVIES, YET. As Billboard recently reported, a certain lyric -- "She looks so perfect standing there/In my American Apparel underwear" -- appears to have prompted a 10 percent boost in that retail chain's sales of briefs. But despite the 5SOS-sized bulge in their bottom line, AA has yet to contact them. "No one at the company has even sent us an email," says Hemmings with a smile. "They’re playing hard to get."

THESE AUSSIES ARE ON A MISSION. The four guys of 5SOS hope to usher in a new wave of young rock bands. "If a kid picks up drumsticks because of our band, job done," says Irwin. "Just to have guitars on the radio again is nice."

GIRLS, GET YOUR DEMOS READY. Long-term plans for the band include branching out into A&R through Hi or Hey Records, the 5SOS imprint distributed by their label Capitol. "A girl version of us would be cool," says Hemmings.

PUNK JUMPS? YEP. F-BOMBS? NOT SO MUCH. The band has made a few minor adjustments on their sold-out tour with One Direction. "We do punk jumps and all that," says Irwin -- but they’ve tempered their language to accommodate 1D’s decidedly younger fan base. "We just don’t ever say 'f—' onstage," he says. "At our own show," says Hemmings, "we talk a lot of shit."

Return to Billboard.com on Monday morning for the full cover story.

BILLBOARD: GET THIS ISSUE | SUBSCRIBE | GET THE iPAD APP