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

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 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

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 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

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 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

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 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

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.

NRA - National Rifle Association Certified Instructor Practice Test

NRA - National Rifle Association Certified Instructor Practice Test

NRA Ballistics & Ammunition 3