The Roth-Sauer is a rare early automatic pistol designed by Karel Krnka, financed by Georg Roth, and manufactured by J.P. Sauer & Sohn in Germany. It is mechanically quite complex – much moreso than strictly necessary. The action is a long-recoil type, in which the bolt and barrel remain locked together through the full rearward travel of the bolt. The bolt then stays to the rear while the barrel recoils forward, clears the empty case, and ejects it. Once the barrel is fully forward, the bolt is released to strip a new cartridge from the magazine and chamber it. The bolt has a single locking lug, which rotates into a recess in the barrel extension to lock.
The firing mechanism on the Roth-Sauer is very similar to the later Roth-Steyr 1907 pistol – and to the modern style of the Glock and others. It uses a striker to fire, which is tensioned to half-cock by the bolt and barrel recoiling with each shot. Full tension on the striker is delivered by the trigger pull, resulting in a approximation of a double-action system. Very much ahead of its day. The Roth-Sauer is chambered for the 7.65mm Roth-Sauer cartridge, which uses a 13mm-long case and it practically identical to the short 7.65mm Frommer (the pistol also shares characteristics with Frommer pistols, as Roth was involved with both designers). It is a quite light cartridge, propelling a 71 grain bullet at 820 fps.