One of gentlemen who joined me to watch Kampfer, Hikago, asked: why didn't Akane use a revolver, since it's so popular in anime? He marked Trigun, Grenadier and Nanoha specifically, and could've added Sakura Taizen.
I swear I'm switching to Hatsuyuki from ep.06 onward.
The question actually goes down to the preference. Observe how Akane's gun is magic, which is why she never needs to reload and needs no place to carry it. The same is actually true for all weapons in Kampfer. For example, Schwert (a bladed weapon) can deflect Natsuru's fire blasts. So, Akane's gun is an expression of a gun rather than a real gun, and thus it took shape of a random piece. It could've looked like revolver as well, but I guess Akane liked it more that way.
Sage, spoilsport as he is, revealed that "one of the [future] red Kämpfer[s] wields two revolvers". Well, there you have it.