Design Details
The PB-4 is a four-barreled break-action gun of original design. It has two horizontal "8"-shaped chambers in its aluminum chambers block, each housing two rounds. There is no need for separated chamber for each round, because gas pressure is contained within thick cylindrical case (external case diameter is 18mm while bullet caliber is 15.3mm), thus chamber support is not needed. Would the round be unlawfully redesigned to increase its power, this will prevent normal use of the gun. The case also performs the function of the barrel, with the bullet positioned deep inside and accelerating within the case. The front end of the case is in level with front end of the chamber block when in firing position. There is a four-fingered extractor in the central channel of the chamber block. Cases are rimless and have an extractor groove. Extractor keeps cases from falling forward outside of chamber block. When action is opened, cases are extracted backwards for manual reloading. The trigger and trigger guard are fixed to lower side of the chambers block.
Chamber block is locked to the handle block with locking surface, firing button (pushed by trigger when chamber block is locked), pistol grip, battery and electronics. Primers are ignited electrically, so there are four circular contact plates on the locking surface (contacting with case bottom) and four contact pins in the center of each plate (contacting with primer). On the trigger pull an impulse is generated. Electronic firing mechanism is able to send firing impulses in sequence to the chambers from 1 to 4 and to skip chambers with malfunctioning rounds to avoid misfires. Weapon is only capable of single-shot firing mode. There are different modifications of PB-4, on some firing mechanism is fed by a battery, on others - by a sort of muscular generator similar with kitchen spark device (a spring is compressed during the trigger pull and electrical impulse is generated by its release).
There is a simple sight assembly atop the chamber block - a semi-cylindrical groove along it and white forward post at the front end of the groove. Some variants of PB-4 have built-in laser sight with laser window in the center of the "locking surface" and the beam following central extractor channel of the chamber block. Laser switch on the left side of the handle block is operated by the thumb. Laser is fed by a battery inside the pistol grip. There are no safety switches - locked and loaded weapon is always ready to fire (for some modifications battery should be live, though)
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