haugenna, the simplest way I can define runout is to say that it refers to how straight or crooked a rifle cartidge is. Cartridges with less runout arestraighter than those withmore runout. One way for you to see this is to take a cartridge and roll it across a flat surface, like a table. While doing this, carfully observe the tip of the bullet.If the tip end of the bullet wobbles as you roll the cartridge, then there is a certain amount of runout present in that cartridge. Another term used in describing whether a cartridge is straight or not is concentricity. A cartridge with little or no runout is said to beconcentric. There are tools for measuring concentricity. My favorite is the one made by Sinclair Int'l.

In practice, cartridges with less runout, those that are concentric, generally tend to shoot more accurately than those with more runout because they are in better alignment with the axis of the rifle's bore. So, if shooting the smallest groups possible is your desire, it's more likely that you'll be able to do it if your ammo has little or no runout. Of course it is nice to shoot the smallest possible groups on paper, I know I enjoy it, but I really can't imagine a little runout ever causing you to miss an animal unless you're shootin' at them way, way out there.