The .308 Winchester (7.62 NATO) Laser Boresight from Sightmark provides a rapid and convenient method for boresighting firearms chambered in .308 Winchester (7.62 NATO). Turn the boresighter on and insert it in your firearm, just as you would chamber a regular cartridge. Orienting your firearm toward a vertical surface, the laser dot will indicate exactly where the barrel is pointed. Stabilize the firearm, and adjust your scope or sight to coincide with the dot; your firearm is now on paper at approximately 15-50 yards, without firing a single shot. Live fire is necessary for determining exact zero, based on distance, load and firearm.This laser boresighter is most useful with firearms having limited access to the breech, such as most semiautos, lever-action rifles and revolvers. Designed primarily for indoor use at short distances, the laser might be visible outdoors too, at distances of up to 50 yards, depending on light conditions. It can save you time and ammo, as it precludes travel to the range and trial-and-error, live-fire based boresighting. The laser is actuated by tightening the end-cap, and will stay on until loosened again. The boresighter comes in a lightweight carrying pouch, which protects the laser for convenient use in the field. It is compatible with all firearms chambered for the .308 Winchester (7.62 NATO) and most cartridges based on it, such as the .243 Win, .260 Rem, .307 Win, .358 Win, 7 mm-08, .256 Win, .220 Jay Bird, etc.