The Advanced Optics Universal Green Boresighter attaches instantly to the muzzle of any firearm and works on all calibers. The magnetic connection to the end of the muzzle provides more precise alignment with the bore without the risk of damaging the bore, compared to arbor style bore devices. It uses a high-power, long-range daylight visible green laser, which runs on a single Lithium CR2 battery (included). Since a green laser is visible at 100 yards or more during the day, it really is the better choice for a boresighter compared to a red laser, which might be visible up to 25 yards. A machined aluminum body with soft rubber over-molding houses the laser module.