As laser technology has become less expensive, laser boresighters have become popular for sighting in rifles. One type of laser boresighter is shaped like a cartridge, and when inserted into the chamber projects a laser beam through the barrel onto the target. The user then adjusts the iron sights or the scope reticle are aligned to the projected laser dot. Another type of laser boresighter is more commonly used and is attached to the muzzle of the barrel, either by inserting into the bore (“arbor” type) or via a magnet, and is held in alignment with the barrel and projects a laser beam onto the target. Again, the user aligns the sights to the laser dot on the target.
No matter which method of bore sighting is used, the result is to align the sights to the spot where the barrel is pointing at a particular distance. Because of variations in the trajectory of ammunition and other factors, the bore-sighted rifle will probably not shoot to that exact spot, and live ammunition will need to be fired to further fine-tune the sighting process.
Accuracy is the measure of how well the sighted object is represented. It can be measured from a specific decision-making circumstance, like the orientation of notches of a gun barrel. Alternatively, the device could be designed to accommodate a range of circumstances and still be sufficiently accurate.