No firearm is of any value unless it can hit what it is aimed at, at least if the shooter does his part. For this to happen, it must be “sighted in”. In the good old days, this often meant actually looking down the barrel from the chamber end and making sure the sight picture and what the barrel was pointing at were the same. Not precision “aiming”, to be sure, but this method would usually get the first shot close enough to where a shooter wanted his gun to hit than when just taking a chance on a first shot hitting on or near a target. This method worked OK on bolt action rifles if the bolt was removed for that look down the barrel, but was not applicable to most other types of actions – especially revolvers and semi-auto handguns.
Some sort of bore sighter greatly speeds up the sighting-in process, by allowing the sights to be initially set to a point even more accurate than looking down the barrel would give. The Collimater type uses a “stem” or arbor sized for the caliber of firearm being sighted in. The stem fits inside the muzzle end of the barrel, and the collimator fits on the stem. Inside the lens and screen of the collimator is a target grid usually set to simulate what a target would look like at 100 yards. Looking at the grid through your scope, the scope windage and elevation settings are moved to put the “center” of the crosshairs where you would like the bullet to hit on the target – dead center or a bit high or low, usually, depending on the trajectory of the cartridge being used. Normally, this technique will at least get a gun “on paper” – especially if starting at 25 yards before moving to a longer distance, so that it can be fine tuned by actually shooting a target at the range. A collimator is also useful for checking your scopes, as it requires no actual down-range target, and if the reticle position on the grid when the scope is actually sighted in is noted, it can be easily and quickly checked to make sure it has not changed due to being jarred somehow.
An update on the standard collimator is the type that uses no arbor, but instead mounts the device on a strong magnet that “sticks” to the muzzle end of the barrel. These types have the advantage of working with almost any gun and caliber, without needing an arbor to fit each one.
The only “drawbacks” to the collimator are it only works with scope sights, and it can be affected by the height of the scope above the bore – which is where the magnet type is handy.
A “more modern” approach to bore sighting uses a “laser pointer” on an arbor that is placed in the barrel and then “shined” at a target to show where the bullet should hit. The scope is then adjusted to “point” at that spot. If the arbor fits correctly, these bore sighters are quick and fairly accurate.
A laser bore sighter also can be used with red dot sights, or even open sights – as well as for adjusting a laser sight on a defensive gun.
The most modern wrinkle in bore sighters is a laser device coupled with a magnet, to fit on the end of the barrel and not require an arbor. This system is perhaps the most versatile of all. I use mine on several different scoped revolvers and one with a red dot sight. I also use it to set the laser sights on my two defensive handguns that wear these, and they can be used to “check” open sights, as well.
All of these devices require final adjustments to the sights or optics be made before they can be considered truly “sighted in”, but they will save a lot of ammo and time in that process, and allow check checks to make sure you will still have a chance to hit what you aim at when you need to.
(Editor’s Note: I have not mentioned the type of last bore sighter that is a cartridge type that fits in the chamber of the firearm, as I have not used these, and so cannot recommend them. Also, it SHOULD go without saying that care must be taken with ANY bore sighter to remove it before actually firing the weapon!)
As a side note, it is still an effective practice to get a first shot on target – by any means – and then adjust the scope to center on the hole that shot made!