The Laser Bore Sight

We are going to talk about lessons learned from the DRE this week. Specifically, we will be discussing a system that is underutilized in the arms room; The Laser Bore Sight. The Laser Bore Sight is used to develop a ballistic compensated zero for optics, lasers, and thermals. It is a more precise method of adjusting a scope than just sighting down the bore of the weapon with the bolt removed (and the upper receiver removed from the lower) onto a target at distance and then adjusting the Optic, Thermal, or Laser to that point.

Picture 1

Picture one illustrates what the LBS looks like.
Picture two illustrates what happens to zero a weapon when you remove the Paratrooper from the equation. There are three things that interact between the optic and weapon in order to hit a target. They are Line of Sight, Line of Bore, and Trajectory. We will start by talking about line of sight.

Picture 2

To put it simply, line of sight is the straight line from the eye through the aiming device (Scope, Iron Sights, Laser) to the point of aim. The line of bore is the line defined by the bore of the rifle or the path the bullet would take without external ballistics acting on it. In other words, if you were to place a laser at the center of the barrel, this is the resulting line.

Why the line of sight, and the line of bore are important are because of the factors that affect the round once it exits the barrel. When a projectile exits the muzzle of a rifle, it drops from the line of bore (LOB), otherwise known as the center-boreline(CBL).

As the projectile travels down range, the velocity is decreased by the effects of external ballistics (the primary effect being drag), thus giving way to the inevitable force of gravity. It is this effect, which creates a trajectory, otherwise known as a parabolic curve.

So essentially, when we zero our weapon, we are adjusting our line of bore, so that it creates a trajectory whose Point of Impact (POI) intersects with our line of sight at the Point Of Aim (POA) on the target. There are certain crossover points in the round’s trajectory, where POA is very close to POI. They are at 10 and 25 meters, hence the reason we Battle-sight zero and Boresight at these distances. Picture four illustrates what a ballistic offset looks like for the laser boresight.

There is much argument over whether the boresight works or not. But when done correctly, the zero that it provides will give you at worst a near solution and at least have you in the target area. A Laser Boresight zero mechanically aligns the line of bore with the line of sight of the optic with a ballistic offset for the appropriate distance. It does need to be confirmed at distance for optics, but is very close. This is of course dependent upon weather conditions (e.g. full-value ten mile an hour wind may affect the accuracy of the zero if not compensated for).

Moreover, the Laser Boresight has a training mode that can be used in conjunction with dry-fire. When the Boresight is put in the ‘pulse’ mode, it operates when the trigger of the weapon is depressed and the hammer drops on the firing pin. The resulting vibration turns the laser on for approximately ¾ of a second, allowing a Paratrooper to triangulate a shot group.

This means that in addition to the dry-fire drills we’ve mentioned in previously, you can utilize this system to work through issues the Paratrooper’s shot process. This provides the Paratrooper feedback on their performance in table I, making them ready to achieve better results in table II.

To sum up, we’ve discussed what the Laser Bore Light is, and the theory behind its application. We will soon discuss how to use this system.

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Raymond Miller
82nd Airborne Division Small Arms Master Gunner: primary weapons trainer, force modernization for individual weapons, and range liason for the 82nd.