When the ammo runs out, I'll be using airguns. Even if I have ammo, for close in and quiet, I'll be using airguns. Of course, I'm not talking about a Daisy BB gun or even a nifty Marksman BB/pellet gun. They're pretty useless for anything more than shooting paper or plastic GI Joes. Something a little more advanced.
This one works well for anything smaller than a Deer out to 100 yds and anything smaller than a Bison under 75yds with a head shot.
Of course they make semi-auto PCP's (Pre-Charged Pneumatics) as well and who wouldn't want a Big Bore in case you stumble across a heard of Bison.
Quackenbush Air Guns
Of course if you want to be really cool, you'll get on the waiting list for Barnes
Barnes Pneumatic Index Page Because this man makes deadly art.
To get an idea of what they make these days browse around this site
Airguns - Browse Air Rifles by Caliber and Air Rifle Manufacturer. There are better retailers, but they have the largest selection.
Most of the PCP's in .22 will shoot 100+ rounds on a charge. To recharge, you can use filled scuba tanks or when they're all gone, a high pressure pump similar to a bike pump. You can also adjust pressure on most of the PCP's. So if you want a close silent shot or just want to save air, dial it down to 600-900 lbs. If it's long range let'er fly at 1500lb+.
Rounds are cheap and can easily be cast at home and because they don't rely on a perfect measure and burn of powder, they are far more accurate than firearms.
If you prefer self contained units, there are several power plants available.
Spring, single pump pneumatic air spring, multi-pump pneumatic are all self contained plants and used by air gun hunters every day.
These and a Big Fuckin' Machete are my post-apocalyptic weapons of choice. A cross bow is another option, I'm just not as familiar with them.
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