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Richard Fortus is a familiar sight onstage in his native St. Louis.

In December, the guitarist joined his former outfit, Pale Divine, for its latest reunion show at the Pageant, and sat in with El Monstero during its recent run at the same venue. Also in 2018, he played (again at the Pageant) with Blackberry Smoke and with Live at Hollywood Casino Amphitheatre.

His primary gig these days, of course, is with Guns N’ Roses, which he joined in 2001. Fortus finally played a hometown gig with GNR at America’s Center in July 2017.

But on Saturday, he will try something a little different and a lot more experimental, joining the funk/rock/electronica/jam-band collective Headtronics for a show at the Old Rock House. The band also includes founding members Freekbass, DJ Logic and Steve Molitz.

“I think it’s going to be awesome,” Fortus says. “But I’m curious to find out what exactly it’s going to be.”

At the point of the interview, Fortus had not yet rehearsed with the band, nor even talked to the other members about how the show was supposed to unfold.

But that’s a feature, not a bug. Headtronics is a wholly improvised experience. Put four veteran virtuoso musicians of different musical backgrounds together, stir, turn up the volume and see what happens.

“From what I understand, we’re starting off with a rough template and just letting things happen,” Fortus says.

A collaboration between Freekbass and Fortus has been a long time coming. “I’ve been a fan of his for a while; I love his playing,” Fortus says. “We’ve always talked about trying to figure out something to do together, and this opportunity just presented itself.”

As for DJ Logic, Fortus says: “He is very, very musical. Everything I’ve heard that guy do is very organic-sounding and doesn’t feel forced.”

Fortus doesn’t know Molitz personally but is familiar with the keyboardist’s work in the jam bands Particle and Phil Lesh and Friends.

Right now, there’s only three Headtronics shows planned — St. Louis, Ardmore, Penn., and Brooklyn, but more may be added later.

Whether Fortus will be part of those shows isn’t yet known. His busy schedule currently includes producing the next album by Psychedelic Furs at St. Louis’ Sawhorse Studios. He’s also recording an album with the electronica artist BT. There’s another major project in the works, he says, but it’s something he can’t talk about yet.

If all of that weren’t enough, there’s his ongoing commitment to Guns N’ Roses. A new album is apparently in the works.

“Slash is on tour right now,” Fortus says. “Once he gets back from that, we’re gonna get some more recording done and hopefully get an album out soon. And then we’ll get back to touring.”

In the meantime, Fortus is happy to try something as loose and spontaneous as Headtronics.

“Generally, the stuff I do is all song-based, where there might be free sections (for soloing and jamming) here and there,” he says. “But this is sort of the opposite of that. It’ll be a cool collaboration, and I’m excited to do it.”

What Headtronics • When 8 p.m. Saturday • Where Old Rock House, 1200 South Seventh Street • How much $25 • More info 314-588-0505; metrotix.com