Designed by Karl Heinemann and manufactured at Solothurn, Switzerland, this rifle was submitted to the late 1920s US Army tests to find a standard-issue semiauto rifle. It was a gas-operated gun using a muzzle cap similar to that of the earlier Bang rifle, but with a toggle lock mechanism reminiscent of the Luger. It was fed by a magazine on the left side of the rifle, and the toggle opened to the right. It weight 9 pounds 6 ounces, and had a total of 114 parts.
The US Ordnance testing board, however, concluded that the Rheinmetall rifle did not merit further consideration because of a poor feeding system, poor cooling, weight, high number of parts, too light of a barrel, poor functioning, and poor sights (one imagines that reading their report would have been quite the hit to Herr Heinemann’s ego).
For more history on the early development of a semiauto military rifle in the US, I recommend Major Julian Hatcher’s excellent work, Hatcher’s Book of the Garand