NRA Ammunition & Ballistics Fundamentals Flashcards

What is 'rifling twist rate' and how does it affect bullet stabilization?

Answer: The rate at which the rifling imparts spin to a bullet — faster twist stabilizes heavier, longer bullets

Twist rate (e.g., 1:10 inches) determines how many inches of travel equal one full bullet rotation; heavier, longer bullets need faster twist to be stabilized.

What is 'case trimming' and when is it necessary in reloading?

Answer: Cutting brass cases back to specified length after they have stretched from firing

Brass cases stretch with each firing, and trimming restores them to the correct length to prevent dangerous chambering issues.

What is the 'ogive' of a bullet?

Answer: The curved forward portion of the bullet that transitions from the bearing surface to the tip

The ogive is the curved nose section of the bullet, and its shape (tangent, secant, hybrid) significantly influences ballistic coefficient and seating depth.

What does 'maximum average pressure' (MAP) represent for a cartridge?

Answer: The highest average chamber pressure considered safe for a given cartridge per SAAMI standards

MAP is the SAAMI-established upper pressure limit for a cartridge, ensuring safe operation across all firearms chambered for that round.

What is a 'wildcat cartridge'?

Answer: A cartridge not standardized by SAAMI, typically created by reshaping existing brass

Wildcat cartridges are custom, non-standardized rounds formed by re-forming existing cases, often for improved performance in specific applications.

What is the purpose of 'annealing' brass cartridge cases during reloading?

Answer: To soften the case neck and shoulder to restore ductility after work-hardening

Annealing applies heat to the case neck and shoulder to relieve work-hardening from repeated firing and resizing, extending case life.