Are you ready for a scorchin’ slice of grrrl power?

Then you’re part of the target audience for the R-rated rambunctiousness of The Runaways, writer-director Floria Sigismondi’s careening and compelling biopic about the mid-1970s all-girl band that smashed through the glass ceiling designed to dissuade young ladies from rocking like the bad boys.

It’s not exactly a complete picture, since Sigismondi, for various reasons, focuses almost entirely on two members of the original Runaways ensemble. Joan Jett — the swaggeringly ambisexual singer-guitarist who continues to perform as an indefatigable hard-rocker — and Cherie Currie — the group’s lead singer who left the music industry years ago, and has more recently made her mark as (no kidding) a chainsaw sculptor — are the featured players.

But even if it’s not the whole story, The Runaways — based in part on a memoir by Currie, and executive produced by Jett — commands attention and stokes emotions. For that, much of the credit must go to its above-the-title lead performers: Twilight star Kristen Stewart, who makes all the right moves as Joan, and all-grown-up Dakota Fanning, who rocks the house and breaks your heart as Cherie.

While promoting The Runaways — which opens today — Stewart and Fanning slowed down long enough to answer a few questions about indie moviemaking and rock ’n’ roll role-playing.

CM: This is a movie about female empowerment, about how, in the 1970s, these girls proved they could rock just like the boys. As actresses, have you ever felt you’ve had to prove yourselves in a similar fashion?

Dakota Fanning: Actually, I’ve grown up always thinking I could do whatever I want, and be whatever I want. I don’t think I’ve ever gone through any struggle compared to what [Cherie Currie and Joan Jett] did. I mean, when I started acting, sure, I didn’t get a lot of things that I wanted. Like, people said I didn’t have enough hair, or I was too blond, or I didn’t have enough experience, so they didn’t want me in their movie. So I experienced things like that. But nothing like they did.

Kristen Stewart: Yeah. Joan always says that nothing has changed whenever she’s asked what’s different in music today. But that’s because she doesn’t see girls literally playing the kind of music that she does. And I don’t think that’s necessarily because things haven’t changed — I think it’s because she’s so unique. And I don’t know if girls necessarily have that drive.

Yeah, we’re definitely put in boxes nowadays. They’re just different boxes. But I think it’s definitely gotten better, because I’ve grown up thinking I could be anything I wanted as well. Joan didn’t. At the same time, though, I think it’s still easier for a guy to have a little bit more personality, or individuality. It’s easier for them to be different, and not have people comment on it as much.

CM: Gee, are you saying that a guy can get away with saying something totally outrageous, but a gal saying the same thing might be considered…. unladylike?

Kristen: Yeah. To a certain degree, definitely.

CM: Were you at all intimidated by the challenge of actually doing your own singing and playing your own instruments?

Dakota: I don’t think it ever occurred to me to not do it myself. I just thought it would be so non-authentic — like, the easy way out — and I really didn’t want to do that. So I always wanted to sing. Of course, it’s a funny thing: Sometimes you jump into something without fully realizing what you’re getting yourself into. We had, like, two weeks to get ready. We had to sort of just do it without thinking, because we really liked it. We’re really not performers in that way. And they have such a distinct, awesome sound.

Kristen: I never, ever got fully comfortable playing the songs while Joan actually was around. Ever. I just had to forget that she was there until they yelled, “Cut!” I mean, she always seemed really happy. And I ‘m sure that even if we were doing really badly, she would have said we were doing well — just to help us do better. But still ...

CM: How did you prepare?

Dakota: Well, I had some voice lessons, and I worked with Cherie on the songs. The performance of “Cherry Bomb” was what I worked on the most, probably. And that was filmed on the second to last day, so I had a lot of practice with that. But Cherie’s personality now is very different than what it was then. And off-stage, she was kind of quiet. I did some research, and I found this interview where she sounds so soft (whispering) like this. And that was so different from her on-stage persona. So I had to work on trying to capture that vulnerability she had, as well as the other stuff.

Kristen: I played guitar before. And that was a good thing, because I had like six songs to learn. But it wasn’t so much playing the songs – Joan plays rhythm guitar, so it was, like, power chords. It was more the way she does it. I don’t do that, I don’t have her mannerisms. But she was with me every single day. And we were able to see Cherie and her together, too, which was also really helpful. Because when they’re around each other, they go right back to when they were with The Runaways. They sort of take on that same dynamic, which was very helpful.

CM: But the emotions are just as important — actually, more important — than the music. You had to make this movie very quickly, on an limited budget. Did that make playing some of the more grueling scenes even more difficult?

Dakota: Well, yes. You see, in every movie, there’s usually about two scenes that are your two really big moments. But in this movie, every little detail of it, every scene was so important, because it was someone’s life, and it really happened to them. We only had six weeks to do the movie, and it was kind of rushed.

Kristen: And there were times when we’d really be working hard on something, and we’d think we’re going to do another take, but it was like, “OK. That’s it. We’re done with that now. That’s just going to be in the movie now. ” It’s not that it was arbitrary. It’s just that, well, that’s the nature of making a small movie.

CM: Do you feel like you could have done some things even better if only you’d had some more time?

Kristen: Oh, my God! Hell, yeah! We loved watching the movie, but (picking up a pencil) I can’t have objects like this is my hand while I’m watching it, because otherwise (lunging forward) I’ll want to go “Arrrgh!”