What makes the final determination about whether or not two bullets were fired by the same gun?

The final determination about whether two bullets were fired by the same gun is primarily made through ballistic comparison analysis. Forensic experts examine the unique striations and markings on the bullets, which are created by the gun's barrel and firing mechanism. Using comparison microscopes, they can match these individual characteristics to determine if the bullets share a common origin. Additionally, test bullets fired from the suspected firearm can serve as a reference for comparison.