Are silencers legal in Idaho?
But Knight Armory does make some nice semi-auto rifles.
I liked their SR-25, it has a very nice barrel.
Anyway if the zombies come, most of the sniper rifles mentioned here are a really bad idea. Lets think about it logically zombies have all the abilities of a human minus any significant thinking skills. But they will probably be able to hear well and use senses as well or maybe better then most people. So the bang from that 50 cal will take down any zombies who are lined up in a mile radius, but it will alert any other zombies to your location. and then its gona be hard to run with that huge rifle. Also as long as ammo is concerned then you need a caliber thats really plentiful in most gun shops which you are going to raid on your way to salvation. Z51 proposed the best choice a silences sniper rifle, in a zombie scenario a silenced weapon is a huge advantage. A system like VSS Vintorez or AS Val would have been a great choice but you'd never find any ammo for it. So the best choice would be a short range silenced sniper, a silenced SMG like HK MP-5SD3 with good glass and set on single shot would be ideal.
But me personally, I'm ready for when the zombie epidemic starts. I'm gonna tie bunch of knives to my hands, put on bullet proof vest and a tactical helmet, I mean lets face it, chances are you are not going to be one of the survivors. So at least I'm gonna be the baddest zombie out there and will live long enough for scientist to discover the cure that will turn zombies to normal people.
P S sorry if I ruined the seriousness of your discussion.