I’ve written before about the RWS/Diana Model 5, which was the first quality air pistol I owned. It’s a fine piece, and unfortunately not made any more, though there are plenty of Chinese copies about. One gun no one seems to have tried to copy is the RWS/Diana model 6, which came in a number of variants. Seen above is the basic 6G model; the 6M had a full barrel shroud and better sights:
The Model 6 used a recoiless system in which two pistons moved in opposite directions. One worked in the usual manner, compressing air and propelling the pellet out of the barrel. The other was a reaction mass, carefully balanced to cancel out the recoil energy from the main piston. This system worked very well, but Feinwerkbau’s simpler sliding receiver system sold better, and the Model 6 disappeared from the market.