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Ballistics terminology

While entering a heavily wooded section on the route of advance, Staff Sergeant Conde-Falcon and his company encountered an extensive enemy bunker complex, later identified as a battalion command post… he maneuvered toward the enemy’s flank position. Carrying a machinegun, he single-handedly assaulted the nearest fortification, killing the enemy inside before running out of ammunition. After returning to the three men with his empty weapon and taking up an M-16 rifle, he concentrated on the next bunker.

-Medal of Honor citation for Staff Sergeant Conde-Falcon

For Walkthrough Wednesday, we are continuing our discussion from the previous week on ballistics; specifically, we will be defining common terminology of ballistics, so we can delve further into this topic. Our reference for this is Appendix B, TC 3-22.9, Change 1 dated January 2017.
To recap, there are three major types of ballistics: internal, external, and terminal. Several key terms are used when discussing the physical actions of internal ballistics

Bore– the interior portion of the barrel forward of the chamber.

Chamber– the part of the barrel that accepts the ammunition for firing.

Grain (gr) – a unit of measurement of either a bullet or a projectile. There are 7000 grains in a pound, or 437.5 grains per ounce.

Pressure – the force developed by the expanding gasses generated by the combustion (burning) of the propellant. Pressure is measure in pounds persquare inch (psi).

Shoulder– the area of the chamber that contains the shoulder, forcing the cartridge and projectile into the entrance of the bore at the throat of the barrel.

Muzzle– the end of the barrel. Throat– the entrance to the barrel from the chamber. Where the projectile is introduced to the lands and grooves within the barrel.

Picture two illustrates where some of these components are inside the M4.

The following terms and definitions are used to describe the actions or reactions of the projectile during flight. This terminology is standard when dealing with any weapon or weapon system, regardless of caliber.

Axis of the bore (Line of Bore) – the line passing through the center of the bore or barrel.

Line of sight (LOS) or gun target line (GTL) – a straight line between the sights or optics and the target. This is never the same as the axis of the bore. The LOS is what the Soldier sees through the sights and can be illustrated by drawing an imaginary line from the firer’s eye through the rear and front sights out to infinity. The LOS is synonymous with the GTL when viewing the relationship of the sights to a target.

Line of elevation (LE) – the angle represented from the ground to the axis of the bore.

Ballistic trajectory – the path of a projectile when influenced only by external forces, such as gravity and atmospheric friction.

Maximum ordinate – the maximum height the projectile will travel above the line of sight on its path to the point of impact.

Time of flight – the time taken for a specific projectile to reach a given distance after firing

Pictures three and four illustrates these terms in relation to external ballistics.

Terminal ballistics is the science of the actions of a projectile from the time it strikes an object until it comes to rest (called terminal rest). This includes the terminal effects that take place against the target. There are two primary terms associated with this:
Kinetic Energy (EK) –a unit of measurement of the delivered force of a projectile. Kinetic energy is the delivered energy that a projectile possesses due to its mass and velocity at the time of impact. Kinetic energy is directly related to the penetration capability of a projectile against the target.

Penetration –the ability or act of a projectile to enter a target’s mass based on its delivered kinetic energy. When a projectile strikes a target, the level of penetration into the target is termed the impact depth. The impact depth is the distance from the point of impact to the moment the projectile stops at its terminal resting place. Ultimately, the projectile stops when it has transferred its momentum to an equal mass of the medium (or arresting medium).

Picture five illustrates this with the M855A1 round. Notice how much penetration is achieved in the ballistic gelatin:

So to sum up, We have defined several terms associated with the various phases of the projectile’s flight. Next week, we will discuss further the preactical application of ballistics.

#weaponsmastery #ballistics

Our hero of the day is Staff Sergeant Conde-Falcon. SSG Conde-Falcon was a part of the famous “Golden Brigade”  which deployed to Vietnam in 1968. You can read more about his actions that earned home the medal of honor at the following link:
https://www.army.mil/medalofhonor/valor24/recipients/conde-falcon/?f=recipients&l=name

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

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