It is a long way to the top if you want to be the biggest heavy metal band in the world. Only Guns N’Roses nailed it first time. For the rest, it is a relentless slog. Most are not good enough and even the ones who have a chance give up, split up or fall out of fashion.

Into the void comes Avenged Sevenfold. The stakes are high, the expectations are great for Hail to the King, their sixth studio album. They have a genuine shot of joining the behemoths who have dominated the genre for so long.

There is only one contemporary band with the crossover appeal, the fan base and the back catalogue to become as big as the likes of Metallica or Iron Maiden. That band is Avenged Sevenfold and they know it.

"I honestly feel like we're that band," their guitarist Synyster Gates recently told Metal Hammer, which sounded liked a declaration of intent. "Our fans are fucking loyal. It's just a question if we've got the songs to attract a billion more of them."

Synyster Gates is one of the reasons why they are where they are; the other is lead singer M. Shadows, known to his friends as Matt and to his fans as Shadows, one of the most compelling characters in hard rock.

Avenged Sevenfold started out in Huntington Beach, California, in 1999. For a long time, it was a "slow underground swell" as Shadows put it. The switch from metalcore to mainstream metal with their third album City of Evil opened up a whole new fanbase, but it was their last album Nightmare which made them global.

Crafted in the trauma that followed the tragic death from a drink and drugs overdose of their drummer Jimmy 'The Rev' Sullivan, in December 2009, Nightmare topped the US Billboard 200.

More importantly, the record had staying power because it contained some of the best work that the band has done to date.

The title track, Buried Alive, So Far Away and Welcome to the Family showcased Avenged Sevenfold's ability to mix tough with tender and to go from ballad to thrash metal, often in the same song.

"What we were really happy about is that, once the dust settled, all of our fans enjoyed and embraced Nightmare and they still embrace it to this day," says Shadows.

"This is really way more important than the first-week sales. The reality is that if a Kanye West or a Lady Gaga puts out a record the same week, you're not going to be number one."

The metal press have been talking up the band’s prospects. They too are desperate for a marquee name to inspire a new generation of hard rock fans.

"Metal Hammer have Brian (aka Synyster Gates) quoted as saying we are going to carry the flag. The reality is that the fans are going to decide that. We're just going to write the best music that we can," says Shadows.

“If our fans get to the point where they catapult us to be one of the biggest metal bands, well we can run with it, we’ll gladly take it and we know we can put on a great live show.”

At their concert in Dublin's Olympia Theatre during the Nightmare tour, it was clear that their audience is predominantly under the age of 25. A generation has passed since metal was arguably the most successful genre in music. The era of bands such as AC/DC, Metallica, Guns N'Roses or even Def Leppard selling tens of millions of records has gone for good.

But there are other prizes. Shadows speaks enthusiastically of Avenged Sevenfold headlining the big metal festivals such as Download, Wacken and Rock in Rio.

Closer to home, the step up from the Olympia to a show in the O2 in December is an indication of how much their fan base has swelled in recent years.

The biggest prize of all is to shake up the music scene, to bring back a “little more of the groove and aggressiveness”, as he puts it, and the new album is squarely in that tradition.

There is the opportunity to be the torchbearers for hard rock in a musical landscape “completely replaced by pop music and alternative music and what I consider rock music for people that hate rock music”.

The band are now in their early 30s. Their whole adult lives have been in the band.

Shadows became a father last year to a boy called River. He praises his own parents as “great, their whole lives revolved around me”, not sentiments you expected to hear, but metal musicians are rarely as aggressive as their public personae may imply.

“His mom, my wife, will come with us on tour. We don’t want him to be raised without his dad. He will create a little bit of calmness on the road. Having a child on the road will help everybody, because he’s such a joy to be around.”

He laments the passing of so many metal musicians most notably the Rev, but every year seems to bring a new casualty – Jeff Hanneman from Slayer being the latest.

“A lot of these guys dedicate their lives to something, they don’t just take music to the extreme, but everything in their life. Being on a tour bus every day and being away from your family causes issues and problems and sometimes people cope with them in different ways.”

I ask him about The Rev and his Irish family. When he died, his family posted a death notice with the words as gaeilge “óg agus saor go deo” – young and free forever.

“When you go to his family gathering, it’s all full on Irish. They sing, they drink and they dance and we don’t do that very much in America. They really keep their Irish heritage close to them. It is pretty cool to see. Even his funeral was full-on Irish.”