Give your shoulder and wallet a break. If you have had to sight in a firearm recently, you know it can be expensive and very hard on the shoulder. Boresighting lets you make sure your sights (iron or scope) point close to where your barrel is pointed. I found an article in wikipedia that said you would break down your firearm so you could look through the barrel the barrel to see what it was pointed at, then adjust your sights to match. A much easier way are the laser boresights. These devices are small lasers placed in a container that matches the ammunition your firearm uses. You turn the device on and insert it into the breach and the beam projects a dot on your target. You then adjust your sights so the cross hairs are on the dot. All is left, then, is to adjust your sights for bullet drop over the distance selected. The boresights can save you a lot of shoulder pain if you are sighting in a high-powered rifle.