Because I have an odd brain, I started wondering how hot your flame aura has to be before it vaporizes the bullets shot at you.
Iron melts at about 1500 degrees Celsius, and that's higher than the melting point of steel or brass, so we're going to use that. The boiling point is about twice that. I looked up some bullet weights under the misguided notion that all I had to do was figure the energy that went into that mass...I digress. Most bullets (as opposed to cartridges) are under 100 grams. There are exceptions, but we're wingin' it, baby.
Now, having looked at the math, I now know why (a) my university physics courses didn't touch heat transfer and (b) I'm not going to calculate the heat transfer. Let's just say that any heat involved has to be intense.
There isn't anything in ICONS about blast furnaces or arc welders. (I know, I'm shocked too.)
But at the heart of it, claiming that the character's fire aura vaporizes the bullets is such a comic book thing to do, so I want to keep hacking at this for a moment.
We could stunt it, treating the flame aura as a force field and the special effect as vaporizing the bullets, but that really seems like a betrayal of the comic-book-ness of it.
Now, military-style heavy weapons are damage rank 7. Incendiary bombs start at damage rank 7, and bullets are deformed in hitting materials of hardness 6 or so. So let's say that fire rank 7 is enough to melt a bullet, which is less than 100 grams of lead, steel, or brass, over a panel or three. Fire rank 8 would vaporize the bullet, if the bullet were in it for a panel or two or three. (Fired bullets hurt the target before then, whether it's rank 7 or 8.)
But rank 9 is in linear terms much more than rank 8. So let's say that any character with a flame aura of 9 or 10 really does vaporize the bullets before they hit his or her skin. Oh, you can still hurt them by dropping a locomotive on them: that's a lot of metal to heat up. But you can treat them as having a force field for the purposes of small flammable projectiles. Concrete would probably hurt, but thrown bottles and cans wouldn't even be noticed.
Of course, I just realized that you could spray them with bullets for a long time and suffocate them by making them breathe in all that vapor they've created....