ELENKER Cal 223 5.56mm Rem Gauge Laser Bore Sighter Boresight Red Dot The laser unit cartridge fits 223REM caliber rifles Simply place batteries in end cap-twist and end cap to turn on-and place in chamber, this product use only 3 batteies. Class 3A laser and laser output less than &lt;5mw Great for the range and ensuring your gun is still zeroed in after travel It projects a straight laser beam allowing precise optical adjustments to sight in your scopes & sights without firing and ammo