The guitarist discusses the group's forthcoming album and plays with them tonight at Comic-Con after-party

Today marks the 31st anniversary of Metallica 's debut album, Kill 'Em All , but guitarist Kirk Hammett will be celebrating his pre- Kill 'Em All life by jamming with his first band, Exodus, at his "Fear FestEvil After Party" tonight at the San Diego Comic-Con International. The gig is an extension of sorts of Hammett's onstage reunion with the band at his Fear FestEvil in February , where he played their song "Piranha" and a cover of Blue Öyster Cult's "Godzilla" with them. Now, he's saying that onstage reunion led to something bigger: "I play a guitar solo on the new Exodus album," he tells Rolling Stone .

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The guitarist reports that after hanging out with founding Exodus drummer Tom Hunting and guitarist Gary Holt, the opportunity came up to play on a song called "Salt in the Wound." "It felt really casual, really cool – just like it did back in 1980 when we were all just hanging out back in the day," Hammett says. "Me, recording a solo on their album was a huge thing for me. Other than the Exodus demo that's been heard by a lot of people, it's the only time I ever recorded with Exodus. It was a huge thing for me."

As for the song itself – which will appear on a record that features the return of Steve Souza, the band's vocalist in the late Eighties and early Nineties – Hammett says it has a "super heavy" riff. "I play a pretty cool solo, and then Gary comes in and plays another solo, and you know what?" Hammett asks. "I listened to that and thought, 'Wow, it's 1982 all over again and here we are, Gary and I are trying to cut each other's heads off with our guitar solos.' Nothing has changed much in the last 30 years. I love it. I love those guys. I've only known them for most of my life, so I'm really happy that I finally got to record with them."

Additionally, Hammett expects the Exodus concert tonight to be a "good old time," as both he and Metallica bassist Robert Trujillo, as well as other unannounced guests, will be joining the band for a unique set. "We're going to be playing 10 or 12 cover songs, but Rob and I are adamant about not playing the usual cover songs that everyone else plays, like 'Communication Breakdown,'" the guitarist says. "People are going to be expecting a bunch of heavy-metal cover songs. There's going to be some of that, but Rob and I, we like to stretch out a little bit so we'll be playing some different stuff, too. We're gonna be playing 'The Real Me' by the Who , which is a song both Rob and I love. And we're going to get funky and play [Kool and the Gang's] 'Jungle Boogie.'"

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Hammett reports that the supergroup will be playing at least one metal classic, though: Ozzy Osbourne 's 1981 song "Diary of a Madman," which Metallica played acoustically at the MusiCares benefit honoring the Black Sabbath singer earlier this year. "I've been jonesing to play that on electric," Hammett says. "Every time we played it acoustic, I've been itching to play it the way I remember hearing it, which is the full-on electric, Randy Rhoads version. Finally I'm going to get my wish and will be playing with Rob and Tom Hunting from Exodus and other people, and it's going to be great."

Hammett's main reason for attending Comic-Con this year is the expansion of his Kirk Von Hammett Toys line, which makes figures of Boris Karloff, Bela Lugosi and, of course, horror enthusiast Hammett in their most iconic horror poses. This year, the guitarist has introduced a zombie figure of himself, which he'll be signing at the convention today and tomorrow.

"It's something that's just really fun for me to do," he says. "I've been a big collector of toys most of my life. Making them helps give me a perspective on what I love, which is horror. I'm really having a lot of fun with all of it. I'm going to be doing the toy line for a while. We're putting out maybe two to three pieces a year."

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Hammett's other deep dive into horror was his 2012 book Too Much Horror Business , which featured photos of his extensive collection of horror memorabilia. Although he had previously said he had plans on making another one, he tells Rolling Stone that he has more pressing matters at the moment. "The band needs to make an album," the guitarist says. "That's the big adventure that's looming up on the horizon. Making an album is always a bit like scaling a mountain, but this time it seems like the more we wait, the bigger the mountain gets. And now that we've been playing so long, it seems like that mountain is as big as the Himalayas right now." He laughs.

Earlier this year, Metallica debuted a new song, "Lords of Summer," on their Metallica by Request tour of South America and Europe (it will wrap with an appearance at Montreal's Heavy MTL fest in August). Hammett says the band looks at that song as the starting point for the new record. "Whether the songs will actually sound like 'Lords of Summer' or not remains to be seen, because we still have to write them, but that's the general direction we're headed in," he says. "I want to make a quick album, but I just know that's not realistic."