Downtune an acoustic

All I have is my acoustic with me right now, and I want to play a downtuned song. Can an acoustic go lower than Drop C? Can it even go to Drop C and still play good? I've never tried to downtune my acoustic because I heard you could damage the neck. Just wondering how low I can play.

I've never tried tuning an acoustic that low. I'd imagine you'd get a lot of fret buzz?