Original Berloque Mini-Pistölchen (Kaliber 2mm) von - Gas & Signal Waffen - Freizeitwaffen - Waffen Online Shop - Frankonia.de
D'you see a theme emerging here?
Loud and destructive, this is handy for distraction - as long as you can get it a good distance away from you before it explodes! Slingshot or an adapted tennis-ball thrower could work. WARNING - do not allow one of these to explode close to anything you want to keep, eg fingers, face, testicles... (I'm not kidding - Google is full of horrifying images of this sort of injury). Alternatively, put one on the end of a long stick and feed it to a zombie...
Of course, if it's a zombie bite, bleeding to death might seem preferable. But silly accidents will happen, even in apocalypse situations...
You've seen the movies. The zombies are roaming the streets, and the roads out of the cities are crammed with abandoned cars. Start looking for back roads, and avoid those built-up areas with an up-to-date road atlas.
No, it probably won't kill a zombie, but it might keep you in game, and a shot to the soft bits could be enough to deter casual scavengers... SWISS ARMS P1911 4.5mm CO2 METAL