If you can't reuse, then stockpile all you can so you have plenty when the zombies get you...
Here are a few links to help you master your ammo making/recycling skills:
Equipment for Bullet Casting: How to Make Your Own Ammunition -- powered by eHow.com
Dealing with Duds: How to Make Your Own Ammunition -- powered by eHow.com
If you need to get perfectly round shell, just drop it off the roof