The framerate they've used varies throughout the image. If you're looking for a base FPS for your own animations, I would start with 0.08s. That's 12fps, and 800ms. It's a good consistent speed, and you can speed and slow things as you wish whilst you're animating. It's also the industry standard, so getting used to 12fps is a good thing.
Personally, I would not advise dropping below 0.05s. While most browsers support down to 0.03s/0.02s, Internet Explorer unfortunately only goes to 0.05s. And rather than going to its fastest speed when something is too fast to handle, it instead defaults to 0.1s. This is absolutely fatal for an animation, as that means your fastest part is your slowest! :c Of course, you can just go 'screw IE', up to you.
i really enjoy the colors you used in this. the girl's design is excellent and it gives me the fuzzies when i see how smooth the animation is. wow look at how much detail you put in the gun!! wow this is really good woW WOW