The Vickers machine gun was an evolution of the Maxim, the world’s first successful machine gun. The Vickers was adopted by the British armed forces shortly before World War I and remained in active service until 1968. It is renowned as one of the most durable and reliable machine guns ever made, with one gun recorded to have fired more than 120,000 rounds in a single 12-hours period in combat. This Vickers has been rebuilt as a semiauto-only gun, and is this not regulated by the NFA and can be sold like any typical rifle or pistol (no tax stamp needed).
For more on the Vickers, see my Paean to the Vickers Gun.