List-2-reasons-why-striations-on-bullets-fired-from-the-same-gun-may-vary-slightly

List 2 reasons why striations on bullets fired from the same gun may vary slightly.

Why would an investigator not pick up a weapon by its barrel with a pencil or stick in order to protect latent fingerprints?

What kinds of impression evidence might a forensic odontologist be asked to analyze?

Basic answers please can be one sentence.