What is this handgun?

In a surprisingly rapid response to my question given their schedule, I got word back from the unit in question. no wonder we were having a hard time deciding what this pistol is. It's a flare gun!

Here is the reply from LTC Steve Russell, the Battalion Commander. (SPC Hoefer is his driver.)

"The pistol is a type 57 Chinese flare gun. We used
many captured flare guns for signaling but mostly to
scare people. They made a hell of a bang and lots of
flash, enough to disperse most crowds, etc. We also
used them against large packs of dogs that seemed to
bark endlesly until scattered by the guns. It was
great fun to watch them scamper. So, it was not
anything fancy, just a flare gun that many of our
soldiers carried in the command convoys."

I feel almost vindicated for not picking up on it. I would never have guessed that one. Now I want to get my hands on one to scare off birds