User blog comment:Kodachi-sama/HINT in the Ruby Trailer??/@comment-5230279-20130303194039/@comment-5043861-20130303232243

The image on it seems to be an implosion (arrows pointing inward to the target/circle), while the white shots (blank?) are the default or explosions.

The shots from the reloading scene to the end are black, but every shot before it is white. Magazines affecting her shot type seems to be true for now.

Also, some good speculation [here].