For a mobile loadout I would want 3 guns. Any mag fed 22lr with lots of mags for long to medium range work (preferably with suppressor), a Saiga 12 gauge for close range, and a sidearm for SHTF situations, probably a 9mm glock 34 with extended mags. While I can relate the idea of sitting on the roof and blast zombies all day, I would prefer to keep a lower profile. The noise would only attract more zombies, and trap you until the zombies die or you starve, or worse, they find a way inside your defenses. They may be dumb but they are persistent and very strong, and will keep battering away until they break through or their arms are stumps. You've got to sleep sometime, in that situation its only a matter of time before you wake up only to be devoured by the horde. My solution would be to gather a small group of friends/family and go find a small island and camp out there, ala 28 Days. I would only use the guns if absolutely necessary, as using them would quickly bring more targets than I have ammo for.
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