Reloading
Also: Handloading
Assembling cartridges from individual components instead of buying factory ammunition. The path to consistent precision and cheap volume.
A handloader starts with fired brass (or new brass), runs it through resizing dies, primes it, drops a measured charge of powder, seats a bullet, and ends up with a finished cartridge. The whole process takes 30 seconds to 5 minutes per round depending on the level of care.
Reloading exists for three reasons: cost (factory match ammo runs $2-3 per round; handloads can be $0.50-1.50), supply (precision components are easier to source than precision factory ammo), and accuracy (a well-tuned handload routinely outshoots premium factory loads in the same rifle).