It is a Zelinka gun, they are made by a number of gunsmiths in Russia and follow the same principle of a moving inner barrel acting as the valve that admits air to the inner barrel when you pull the trigger. Pelengas make a form of Zelinka, but it lacks the power regulator switch at the rear and instead has a hand pump attachment in the rear of the gun. Zelinka type guns use the inner barrel as the hand pump with the spear being used as the pump rod. The muzzle is adjusted in a forward position for pumping so that air is admitted to the gun on each pump stroke through the muzzle relief ports, the piston seal being able to escape contact with the inner barrel bore at the top of the pump stroke.
Whether the gun floats after the shot given the diameter of the tank depends on the materials used and the buoyancy provided by the handle. Titanium being heavier than aluminium it requires more design effort to make such guns float, although the longer the gun then there is more tank volume to make the gun a floater.
Well just when I proclaim that a titanium gun will be a sinker unless it has a significant tank capacity to provide enough water displacement for it to float after the shot, one gets offered on eBay via the Pelengas store that does float, or so it is claimed on the item description.This all...
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