NRA Ballistics & Ammunition — Questions and Answers

Question 1: Which branch of ballistics studies the behavior of a projectile after it leaves the muzzle and before it reaches the target?

Internal ballistics
External ballistics (Correct answer)
Terminal ballistics
Wound ballistics

Correct answer: External ballistics

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

Question 2: In ammunition terminology, what does 'grain' measure?

The length of the cartridge case
The weight of a projectile or powder charge (Correct answer)
The diameter of the bullet
The pressure generated by ignition

Correct 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.

Question 3: What is 'headspace' in firearm and ammunition terminology?

The distance between the front sight and the rear sight
The gap between the trigger and the trigger guard
The distance from the bolt face to the point in the chamber that stops forward cartridge movement (Correct answer)
The space inside the magazine above the top round

Correct 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.

Question 4: What causes a 'squib load' and why is it dangerous?

Excessive powder charge that generates dangerously high pressure
Insufficient powder or primer failure leaving the bullet lodged in the barrel, causing a potential obstruction (Correct answer)
A cartridge loaded with the wrong caliber bullet
A primer that ignites late after the trigger is pulled

Correct 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.

Question 5: What is 'muzzle velocity' as it applies to ammunition performance?

The rotational speed of the bullet as it travels downrange
The speed of the bullet as it exits the muzzle of the firearm (Correct answer)
The rate at which the powder charge burns inside the case
The velocity at which the bullet impacts the target

Correct 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.

Question 6: Which of the following best describes a 'sabot' round?

A bullet coated with a lubricant to reduce barrel friction
A sub-caliber projectile housed in a carrier that is discarded after leaving the muzzle (Correct answer)
A bullet designed to expand upon impact with the target
A cartridge loaded with multiple small projectiles

Correct 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.

Question 7: What are the four components of a standard centerfire cartridge?

Primer, case, powder, and wad
Case, bullet, powder, and primer (Correct answer)
Bullet, jacket, core, and propellant
Shell, powder, slug, and cap

Correct answer: Case, bullet, powder, and primer

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

Question 8: What does 'FMJ' stand for and what is its primary design characteristic?

Full Metal Jacket — a bullet with a soft lead core enclosed in a harder metal shell (Correct answer)
Full Magnum Jacketed — a high-pressure round with a reinforced case
Forward Metal Jacket — a bullet with extra weight at the front for stability
Fixed Metal Joint — a sealed primer that cannot be reloaded

Correct 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.

Question 9: What is 'terminal ballistics'?

The study of how a bullet behaves inside the barrel during firing
The study of how a projectile behaves upon impact with a target (Correct answer)
The study of maximum range a bullet can travel
The study of bullet trajectory during its flight

Correct 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.

Question 10: What is the key difference between a rimfire and a centerfire cartridge?

Rimfire cartridges are larger in caliber than centerfire cartridges
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 (Correct answer)
Rimfire cartridges use smokeless powder while centerfire cartridges use black powder
Rimfire cartridges are reloadable while centerfire cartridges are not

Correct 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.

Question 11: What is 'ballistic coefficient' (BC) and how does it affect bullet performance?

A measure of how much a bullet expands upon impact, with higher values indicating greater expansion
A numerical value describing a bullet's ability to overcome air resistance; higher BC means less velocity loss over distance (Correct answer)
A rating indicating the maximum safe chamber pressure for a given cartridge
The ratio of bullet weight to barrel twist rate required for stabilization

Correct 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.

Question 12: What causes 'keyholing,' and what does it indicate about the ammunition or firearm?

The bullet is too heavy for the barrel twist rate, causing it to tumble and strike the target sideways (Correct answer)
Excessive barrel heat is melting the bullet jacket, causing irregular impact patterns
The bullet is striking the target at a steep angle due to an obstructed sight line
A worn or damaged crown at the muzzle is causing the bullet to veer off course

Correct 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.

Question 13: What is 'sectional density' (SD) and why is it important to hunters and instructors?

The ratio of a bullet's diameter to its length, used to determine optimal barrel twist rate
The ratio of a bullet's weight to the square of its diameter, indicating potential penetration capability (Correct answer)
The measurement of how uniformly the bullet's core is distributed within the jacket
The ratio of powder charge weight to bullet weight, used to calculate maximum pressure

Correct 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.

Question 14: What is 'overpressure' ammunition (indicated by '+P' or '+P+') and what precaution must an NRA instructor communicate to students?

'+P' ammunition is loaded to lower-than-standard pressure for reduced recoil and is suitable for all firearms
'+P' ammunition is loaded to higher-than-standard pressure for increased velocity and must only be used in firearms rated for it (Correct answer)
'+P' ammunition uses a different primer type and is incompatible with standard firing pins
'+P' ammunition is a military designation meaning armor-piercing and is illegal for civilian use

Correct 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.

Question 15: What does 'twist rate' refer to in a rifle barrel, and how does it affect bullet selection?

The angle at which the barrel is threaded for a muzzle device, affecting suppressor compatibility
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 (Correct answer)
The speed at which the action cycles during semi-automatic fire
The number of lands and grooves cut into the barrel, affecting friction and velocity

Correct 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.

Question 16: What is a 'hollow point' bullet designed to do upon impact, and in which context is it commonly recommended for self-defense?

Penetrate deeply without deforming, maximizing wound channel depth in soft tissue
Expand upon impact to create a wider wound channel and reduce the risk of over-penetration (Correct answer)
Fragment into multiple pieces to increase the area of tissue damage
Deflect off hard surfaces to reach targets around cover

Correct 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.

Question 17: What is 'copper fouling' in a firearm barrel, and how does it typically occur?

Oxidation of the steel barrel caused by exposure to moisture and humid air
Deposits of copper or copper alloy left in the bore by the bullet jacket as it travels down the barrel (Correct answer)
Contamination of the powder charge by copper residue from the primer
A reaction between the brass cartridge case and the chamber walls under high pressure

Correct 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.

Question 18: What is 'trajectory' and what are the two primary forces that shape a bullet's trajectory after it leaves the muzzle?

The bullet's rotational path; shaped by twist rate and barrel temperature
The curved flight path of the bullet; primarily shaped by gravity pulling it downward and air resistance slowing it (Correct answer)
The straight-line path the bullet travels; determined solely by muzzle velocity
The bullet's path as deflected by crosswinds; determined by bullet diameter and wind speed

Correct 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.

Question 19: What is 'hydrostatic shock' and why is it a topic NRA instructors should understand when discussing terminal ballistics?

The recoil force transmitted through the action into the shooter's body when a high-powered round is fired
The pressure wave generated by a high-velocity projectile traveling through fluid-containing tissue, potentially causing damage beyond the direct wound channel (Correct answer)
The shock to the firearm's internal components caused by overpressure ammunition
The hydraulic pressure created in a suppressor when wet suppressant is used

Correct 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.

Question 20: When selecting ammunition for a specific firearm, what is the most critical compatibility factor an NRA instructor should teach students to verify first?

The ammunition's brand reputation and country of manufacture
That the caliber and chamber designation on the ammunition matches exactly the caliber stamped on the firearm (Correct answer)
That the ammunition's muzzle velocity matches the firearm manufacturer's recommended FPS range
That the bullet weight in grains does not exceed the maximum listed in the owner's manual

Correct 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.

Question 21: What is the purpose of a 'cannelure' on a bullet, and why is it relevant to ammunition reliability?

A cannelure is a coating applied to the bullet to reduce barrel friction and improve velocity
A cannelure is a groove crimped into the bullet near the base or middle to allow the case mouth to be crimped into it, preventing bullet setback (Correct answer)
A cannelure is a hollow cavity at the base of the bullet to improve gas sealing
A cannelure is a color-coded band identifying the bullet's intended use (e.g., hunting vs. target)

Correct answer: A cannelure is a groove crimped into the bullet near the base or middle to allow the case mouth to be crimped into it, preventing bullet setback

A cannelure is a rolled groove around the bullet that allows the case mouth to be crimped into it, securing the bullet and preventing it from being pushed back into the case during feeding, which could dangerously increase pressure.

NRA Ballistics & Ammunition

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

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Sources & references

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