http://www.rockislandauction.com/viewitem/aid/67/lid/1525

In 1928 and 1929, the Swiss Rheinmetall company produced about 50 examples of a toggle-locked rifle designed by Karl Heinemann. It was tested by the United Stated among other countries, but never found military acceptance. This particular example is a Hienemann rifle in sporting pattern, made by the Walther company. I do not know the details of Heinemann's move form Rheinmetall to Walther, but I would guess it had to do with his early rifles' lack of military success.

Mechanically, the gun is quite unusual and interesting, with a toggle-locked bolt and a Bang-type muzzle cup. Gas is captured in this cup when the rifle is fired, and that pressure pulls the muzzle cup forward. An operating rod runs form the muzzle back to a cam which cracks the bolt toggle open when it is pulled forward, thus unlocking the action.