Answer #1: Kaff Tagon is firing 10mm exploding rounds from a hybrid gauss/gunfoam pistol. In pure 'gausspistol' mode the weapon is fairly silent, propelling iron-core flechettes at just under the speed of sound. Silent is good, and flechettes are excellent anti-personnel rounds.
Suppose you want to pack more punch than a flechette, though. In gunfoam mode the weapon can launch longer, explosive rounds without risking the mag-pulse of gauss mode fouling the detonation circuitry. Gunfoam goes "BLAM." The explosive rounds also go "BLAM," but at point blank range it's all pretty much one noise. And depending on where you are standing, you won't get to hear it at all. Or maybe you'll just get the "BL" part, and stop wondering what's happened by the time the "AM" reaches you.
Answer #2: Most comic-book handguns go "BLAM" regardless of how the author thinks they work. Because of this, the above explanation is fairly pointless. Forget I said anything.