The 223/5.56 Laser Bore Sight Module With External Battery Box works with two AAA batteries for much longer run time compared to the original internal battery design. Designed to make it quick and easy to bore sight your rifle chambered in .223/5.56. This laser is also the basis for the AimSHOT rifle caliber laser bore sight system and is used in conjunction with the AimSHOT Rifle Arbors to bore sight most major rifle calibers. Insert brass laser module into chamber and align scope reticle to match laser beam at 20 yards. Remove laser and proceed to the range for final adjustments at whatever range you want your zero.