The Browning Auto-5 is a semi-automatic shotgun designed by John Browning and introduced in 1900. It was one of the first successful semi-automatic shotguns and is known for its distinctive humpbacked receiver. The Auto-5 operates using a long-recoil system, where the barrel and bolt move together during firing, allowing for quick follow-up shots. This shotgun was produced in various gauges, including 12, 16, and 20, and became popular among hunters and sport shooters. The Browning Auto-5 remained in production until 1998, with over a million units sold, making it a significant model in the history of firearms.