Here too, I've never encountered anyone who considered firearms (useage) a martial art. Now we're not talking Iraq here. I've only my Bureau training, S&W training and visits to my local range buddies to base this on.
What a rare and welcome opportunity to spread the word!
Most people who practice both a more "traditional" martial art as well as firearms for Self Defense (SD) or combat consider their firearms training to be a "martial art" as well. It's very, very common. Take a look at the usenet forum rec.martial-arts as an example of a forum that runneth over with people who consider firearms training a "martial art."
Considering that "martial" (in this context) means roughly "of, deriving from, or having to do with war or combat" and "art" being a refined skill, firearms skill applies just as easily as kyudo/kyujutsu, being essentially exactly the same martial art excepting the substitution of the firerarm for the bow. Continuing that thought, I point you to the Japanese "Martial Art" of Jukendo, which is rifle-with-bayonet fighting (a
subset of firearms use). In continuation of the theme, note that, besides the obvious martial and SD application, firearms training, in many cases, bears all the halmarks of any other "traditional" (i.e. oriental) martial art in that qualified and certified istructors teach students, there are numerous bodies organizing various aspects of training such as sport competition and SD targeted yet competitive outlets. Further, many of these organizations issue multiple levels of
ranking for acquired and demonstrated skill in the "art" such as Marksman, Pro Marksman, Marksman First Class, and Sharpshooter.
The only thing that it lacks in making it a "martial art" in the minds of some is white pyjamas and calling the rank 'shodan' instead of 'sharpshooter'.
Seriously, you should look into the body skill, and commitment required for SD or Combat related study of the art of firearms use and base your consideration of whether or not its a "martial art" upon that. I think you'll find yourself pleasantly surprised.
Oh, but like a top level set of Kendo gear, bring your wallet.
Peace favor your sword,
Kirk