303BR Brass Red Laser Boresight. Caliber-matched brass bore sight exclusively for .303 British barrels, made of premium solid brass for tight barrel fit. It adopts a 635-655nm visible red laser with safe output below 5mW, delivering clear aiming dot from 10 to 80 yards, with a 1.5-inch dot at 100 yards for easy optic alignment. 50g lightweight brass cartridge inserts easily into barrels, allowing fast pre-zero calibration to save ammunition for hunting and range practice.