Ballistics & Ammunition Flashcards

Which branch of ballistics studies the behavior of a projectile after it leaves the muzzle and before it reaches the target?

Answer: External ballistics

External ballistics covers the projectile's flight path from muzzle to target, including factors like gravity, wind, and air resistance.

In ammunition terminology, what does 'grain' measure?

Answer: The weight of a projectile or powder charge

Grain (gr) is a unit of weight equal to 1/7,000 of a pound, used to measure both bullet weight and powder charge weight.

What is 'headspace' in firearm and ammunition terminology?

Answer: The distance from the bolt face to the point in the chamber that stops forward cartridge movement

Headspace is the distance from the bolt face to the datum line in the chamber that stops the cartridge from moving forward; incorrect headspace can cause dangerous malfunctions.

What causes a 'squib load' and why is it dangerous?

Answer: Insufficient powder or primer failure leaving the bullet lodged in the barrel, causing a potential obstruction

A squib load occurs when insufficient powder or a defective primer fails to fully propel the bullet, leaving it stuck in the barrel; firing another round into an obstructed barrel can cause catastrophic failure.

What is 'muzzle velocity' as it applies to ammunition performance?

Answer: The speed of the bullet as it exits the muzzle of the firearm

Muzzle velocity is the speed of the projectile at the moment it leaves the barrel, typically measured in feet per second (fps), and is a key factor in external ballistics.

Which of the following best describes a 'sabot' round?

Answer: A sub-caliber projectile housed in a carrier that is discarded after leaving the muzzle

A sabot is a sleeve or carrier that allows a smaller-diameter projectile to be fired from a larger-bore barrel; the sabot falls away after the bullet exits the muzzle.

What are the four components of a standard centerfire cartridge?

Answer: Case, bullet, powder, and primer

A centerfire cartridge consists of the case (brass), bullet (projectile), powder (propellant), and primer (ignition source).

What does 'FMJ' stand for and what is its primary design characteristic?

Answer: Full Metal Jacket — a bullet with a soft lead core enclosed in a harder metal shell

FMJ (Full Metal Jacket) bullets have a soft lead core enclosed in a harder metal (usually copper or gilding metal) jacket, which reduces barrel fouling and increases penetration.

What is 'terminal ballistics'?

Answer: The study of how a projectile behaves upon impact with a target

Terminal ballistics examines what happens when a projectile strikes a target, including penetration, expansion, energy transfer, and wound channel formation.

What is the key difference between a rimfire and a centerfire cartridge?

Answer: Rimfire cartridges have the primer compound in the rim of the case; centerfire cartridges have a separate primer in the center of the case head

In rimfire cartridges the priming compound is spun into the hollow rim of the case, while centerfire cartridges use a separate replaceable primer seated in the center of the case head.

What is 'ballistic coefficient' (BC) and how does it affect bullet performance?

Answer: A numerical value describing a bullet's ability to overcome air resistance; higher BC means less velocity loss over distance

Ballistic coefficient is a measure of a bullet's ability to resist aerodynamic drag; a higher BC means the bullet retains velocity better over long distances.

What causes 'keyholing,' and what does it indicate about the ammunition or firearm?

Answer: The bullet is too heavy for the barrel twist rate, causing it to tumble and strike the target sideways

Keyholing occurs when a bullet is insufficiently stabilized by the barrel's rifling twist rate and tumbles in flight, leaving an elongated key-shaped hole in the target instead of a round hole.

What is 'sectional density' (SD) and why is it important to hunters and instructors?

Answer: The ratio of a bullet's weight to the square of its diameter, indicating potential penetration capability

Sectional density is the ratio of a bullet's mass to its cross-sectional area; a higher SD generally indicates better penetration, which is important in hunting to reach vital organs.

What is 'overpressure' ammunition (indicated by '+P' or '+P+') and what precaution must an NRA instructor communicate to students?

Answer: '+P' ammunition is loaded to higher-than-standard pressure for increased velocity and must only be used in firearms rated for it

+P and +P+ ammunition is loaded to pressures above SAAMI standard specifications for that caliber and should only be used in firearms specifically rated by the manufacturer to handle the extra pressure.

What does 'twist rate' refer to in a rifle barrel, and how does it affect bullet selection?

Answer: The rate at which the rifling causes the bullet to rotate, expressed as one full rotation per a given number of inches; faster twist stabilizes heavier/longer bullets

Twist rate (e.g., 1:10 means one rotation per 10 inches) describes how fast the rifling spins the bullet; heavier and longer bullets generally require a faster (lower number) twist to be properly stabilized.

What is a 'hollow point' bullet designed to do upon impact, and in which context is it commonly recommended for self-defense?

Answer: Expand upon impact to create a wider wound channel and reduce the risk of over-penetration

Hollow point bullets are designed to expand (mushroom) upon impact with soft tissue, creating a larger wound channel while reducing over-penetration, making them popular for self-defense.

What is 'copper fouling' in a firearm barrel, and how does it typically occur?

Answer: Deposits of copper or copper alloy left in the bore by the bullet jacket as it travels down the barrel

Copper fouling occurs when the copper or gilding metal jacket of a bullet scrapes against the bore's rifling under high pressure, leaving copper deposits that can degrade accuracy if not cleaned.

What is 'trajectory' and what are the two primary forces that shape a bullet's trajectory after it leaves the muzzle?

Answer: The curved flight path of the bullet; primarily shaped by gravity pulling it downward and air resistance slowing it

Trajectory is the curved path a bullet follows in flight; gravity continuously pulls it downward while aerodynamic drag slows it, causing the arc-shaped path seen in ballistic charts.

What is 'hydrostatic shock' and why is it a topic NRA instructors should understand when discussing terminal ballistics?

Answer: The pressure wave generated by a high-velocity projectile traveling through fluid-containing tissue, potentially causing damage beyond the direct wound channel

Hydrostatic shock refers to the remote wounding effect from a pressure wave transmitted through tissue fluids by a high-velocity projectile; it is relevant when discussing wound ballistics and bullet performance in self-defense and hunting contexts.

When selecting ammunition for a specific firearm, what is the most critical compatibility factor an NRA instructor should teach students to verify first?

Answer: That the caliber and chamber designation on the ammunition matches exactly the caliber stamped on the firearm

The caliber marked on the ammunition must exactly match the caliber stamped on the firearm's barrel or receiver; using mismatched calibers can result in catastrophic firearm failure and serious injury.