Two small points. Why does anyone try to quantify the Joker's weapons? He's a psycho in the purist form of the word. So yea, one of his hold outs is a sharpened potato peeler, and he'll use any weapon he can get his hands from crowbar to plastic explosives.
Two, when Batman bends the barrel it very obviously shows the new servo-system in his arms doing the work, you will even hear a high-pitched gyro whine. They are used again when he cuts into the van's side.
Lastly, yea thats three not two, whatever, as much as I like examining the guns in movies, it is based on a comic book, so if there is a ".28 calibre polymer made in China gun" that doesn't fire, there's a guy in a blue and red suit from an alien planet that teams up with Batman all the time too, let's give them some fictional leeway.
