The Popcap pistol is named after it's firing sound, many soldiers having reported it's quieter and lighter than a 'real firearm should.' The sound is due to the unorthodox round used by this weapon. They are similar rounds to the ones used by [link]
The three barrels help keep the weapon in working order as the new rounds work, exploding just outside the barrel in a sort of sawd off shotgun type spread.
Manufacturer's Note: any collateral damage is just too bad. You took this monster out of it's holster, armed it, aimed, and fired it. Everything in front of you you should have wanted dead anyway.