How Does a Bore Sight Work?
What is Bore Sighting
Bore sighting is a method of aligning a firearm's sighting system with the barrel. The purpose of a bore sight is to facilitate this process. Bore sighting saves time and ammunition, as it puts the sights or scope close to the correct position without firing.
Modern laser bore sights make the job of sighting in a rifle or handgun with a scope or open sights very easy. The laser bore sight fits into the chamber of the firearm. Once the laser is turned on, the firearm is aimed at the target and the scope or sights are aligned to aim at the laser dot on the target. In an ideal world without wind, air resistance or gravity, the firearm would be dead on without further need for sighting.
Get on Paper
Follow safe firearm-handling practices at all times. Open the firearm action to ensure it is unloaded. Keep the firearm pointed downrange. Treat every firearm as if it is loaded. Place a new paper target downrange at 25 yards for a rifle or 25 feet for a handgun.
Clamp the firearm into a firearm vise or rest it on sandbags and insert the laser bore sight into the chamber of the firearm.
Look through the scope without touching the firearm. You will find that the cross hairs do not align with laser's red dot. Without moving the firearm, turn the scope's horizontal (windage) and vertical (elevation) adjustment wheels one click at at time until the cross hairs are centered on the red laser dot. Adjustable rear open sites are moved manually, but the procedure is the same.
Fire a single round at the target to confirm the alignment. Remove the bore sight and place a single round in the chamber. With the cross hairs on the target center, fire the round and observe the location of the bullet hole. The bullet hole in the paper target should be less than an inch from the center. In most cases, it will be very close to center. You can now proceed to sight the firearm in at a longer range.
Extending the Range
Place a new target downrange at 100 yards (25 yards for a handgun or .22 rifle). At the bench, place the laser bore sight back in the chamber. Using the vise or sandbags, adjust the firearm to put the laser dot on the target. Look through the scope. You should be very closely aligned with the laser dot.
Adjust the elevation and windage to align the scope with the laser's red dot on the target. The final adjustments will have to be made while firing the firearm, but the bore sighting is complete. Final sight in should be with groups of three rounds fired between adjustments until the firearm shoots within an inch of the target center.
Note: If you laser bore sight a firearm and the actual impact point while firing differs significantly at longer ranges from the red dot, there is a problem with the boring of the rifle and you should have it examined by a competent gunsmith.
Michael Logan is a writer, editor and web page designer. His professional background includes electrical, computer and test engineering, real estate investment, network engineering and management, programming and remodeling company owner. Logan has been writing professionally since he was first published in "Test & Measurement World" in 1989.