Jokers' gun in "The Killing Joke"

Question

Before I watched the movie "The killing joke" I read the comic again. I was always wondering why the gun of the joker has two barrels. Can it be possible that the main barrel is just used to trigger the flag with the words "click click click" on it?

The second barrel could be the "real" one that actually shoots bullets.

This theory could mean, that the joker had the opportunity to kill batman, but he decided to let the game go and just released the flag.

Has anybody ever thought about this? Here is a picture of that special gun.

Answer 1

Barrels

That is not a second barrel. It is the slide for emptying rounds from the cylinder.

On old style revolvers, the entire cylinder does not pop out to allow for speed loading. Instead, you open a latch and use the ejector rod which runs along side the barrel to individually eject spent rounds from the cylinder.

You can see it on single-action revolvers.

Here is a revolver without the casing around the ejector rod that demonstrates how it works.

Click Click Click

As far as the Click Click Click flag. It is more likely he has a special bullet loaded which pushes out the flag.

Answer 2

I just looked at my Killing Joke, and Joker clearly says

God damn it... It's empty!

Surely, he could be lying.

We see that the flag comes out of the bigger barrel. When Joker shoots Barbara, it is unclear whether the bullet exits from bigger barrel or smaller one.

Anything else is really just speculation, although I clearly remember at least one (old) comic where Batman was caught off-guard and incapacitated, and Joker let him live while he could finish him off.