NRA Ballistics & Ammunition 3

Question 1

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

Accepted 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

Answer

The angle at which the barrel is threaded for a muzzle device, affecting suppressor compatibility

Answer

The speed at which the action cycles during semi-automatic fire

Answer

The number of lands and grooves cut into the barrel, affecting friction and velocity

Question 2

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

Accepted Answer

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

Answer

Penetrate deeply without deforming, maximizing wound channel depth in soft tissue

Answer

Fragment into multiple pieces to increase the area of tissue damage

Answer

Deflect off hard surfaces to reach targets around cover

Question 3

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

Accepted Answer

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

Answer

Oxidation of the steel barrel caused by exposure to moisture and humid air

Answer

Contamination of the powder charge by copper residue from the primer

Answer

A reaction between the brass cartridge case and the chamber walls under high pressure

Question 4

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

Accepted Answer

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

Answer

The bullet's rotational path; shaped by twist rate and barrel temperature

Answer

The straight-line path the bullet travels; determined solely by muzzle velocity

Answer

The bullet's path as deflected by crosswinds; determined by bullet diameter and wind speed

Question 5

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

Accepted Answer

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

Answer

The recoil force transmitted through the action into the shooter's body when a high-powered round is fired

Answer

The shock to the firearm's internal components caused by overpressure ammunition

Answer

The hydraulic pressure created in a suppressor when wet suppressant is used

Question 6

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

Accepted Answer

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

Answer

The ammunition's brand reputation and country of manufacture

Answer

That the ammunition's muzzle velocity matches the firearm manufacturer's recommended FPS range

Answer

That the bullet weight in grains does not exceed the maximum listed in the owner's manual

Question 7

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

Accepted 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

Answer

A cannelure is a coating applied to the bullet to reduce barrel friction and improve velocity

Answer

A cannelure is a hollow cavity at the base of the bullet to improve gas sealing

Answer

A cannelure is a color-coded band identifying the bullet's intended use (e.g., hunting vs. target)