Most gun violence is committed by males, yet most males do not commit acts of gun violence, indicating that some aspect of masculinity that varies among males might account for this incongruence. I proposed that masculine gender role discrepancy strain, in combination with acquired capacity for gun violence, might account for why some boys and men commit acts of gun violence. The evidence for the role of discrepancy strain in the perpetration of violence was reviewed, with support coming from correlational studies, experiments, and qualitative studies in four social science disciplines: psychology, sociology, criminology, and cultural anthropology. This research suggested that males who feel that they do not measure up to their own standards for masculinity, or who are induced to feel that way after their masculinity is threatened, are likely to react violently. Furthermore, additional evidence linked discrepancy strain to three forms of actual gun violence: school shooters, mass shooters, and murder-suicides. I next examined the plausibility of the construct of acquired capability for gun violence, reviewing work on gun ownership, gun carrying, and gun enthusiasm. I concluded by providing recommendations for research and public education. In regard to the latter, I recommended that psychologists speak with parents, teachers, coaches, and other professionals who interact with boys to persuade them to carefully consider the messages that they are sending to boys.