22 Long Rifle, or . 22 LR, is by far the least expensive, averaging about 10 cents per round over the past two and a half years.

Green tip ammo is made to penetrate steel, which makes it very strong. The damage it can do is what makes it controversial for civilian use. This superior ammo was originally created to penetrate armor. It's considered dangerous by many, but nonetheless is legal to own in the United States.

In terms of shelf life, ammunition generally doesn't expire or go bad. Many manufacturers will list an expiration date of ten years past the manufacturer date, but that's more for legal reasons than it is for safety reasons. If it's stored correctly, then there's no real known limit to how long you can keep ammunition.

One of the most common rounds world-wide is . 22LR ammo. It's easy to find both pistols and rifles chambered in this rimfire round.