For anyone interested, the guys on Sons of Guns made 2 Zombie Killing Guns along with Max Brooks on the last episode.
It was fun.
One was an M-16 with a 37mm grenade launcher, bayonet, suppressor(don't want them to hear you), and some nice optics.
The other was a .22 magnum rifle(most plentiful ammo in the world) converted to a bullpup design with a custom attachable spike and optics.