Samuel McClean was a medical doctor from Iowa who began tinkering with firearms designs in 1889, and formed the McClean Arms Company in 1896. He was an intelligent and talented designer, but never quite managed to get a gun good enough for military acceptance. His work included bolt actions rifles, self-loading shoulder rifles, machine guns, and self-loading cannons. By 1910 his company had gone bankrupt twice, and he was forced out by his investors. Isaac Newton Lewis was brought in, and turned McClean’s initial concepts into the ultimately-successful Lewis Machine gun.

However, McClean made one least attempt to produce his own gun after World War One. This is the McClean Automatic Rifle, and it was tested by the US Navy in 1919 - and rejected. This pattern uses an operating system similar to McClean’s early work, and thus also quite similar to the Lewis gun. Instead of two large locking lugs, however, it has several dozen small lugs in two rows on each side of the bolt. The gas piston is also huge by modern standards; over an inch in diameter. The gun is unfortunately missing its magazine Still, it is the only example of the type known to exist, and probably the only one ever manufactured.