The hole in the middle of the rear of the slide routes the gas behind the BB. In the front you can see the brass tube for the blowback, and the recoil spring around the outer barrel.
SHELL-EJECTING GAS BLOWBACK MADNESS!
Marushin from Japan has a long history of quite interesting airsoft models as well as PFC (Plug Fire Cartridge) models, aka. model guns or cap guns. While they have the obvious M9 and 1911 models in their selection, they were never afraid to try something different. This goes for both the models they selected to replicate, but in this case also the operating method.
Shell ejecting gas blowback is a combination many have deemed impossible to achieve in a pistol, but Marushin managed to pull it off over a decade ago! How is this possible? A brief explanation is in order: The BBs are loaded into shells, which are loaded into a realistically sized magazine. No room for gas in there as well, so Marushin has made the entire back of the grip into a gas tank! It is filled from the heel of the grip, and you can actually feel it cool down if you shoot rapidly.
When you first pull the trigger, the hammer falls and strikes the valve to route gas behind the BB. The BB is shot out, and if you "feathered" the trigger, the slide won't move. Pulling the trigger completely actuates another valve, which routes the gas into the blowback chamber. Because a loading nozzle would not have time to move back to feed a full length cartridge if it was placed into the rear of the slide, the entire GBB system has been moved into the front of the slide below the barrel. As the pistol needs a recoil spring as well, it is placed around the outer barrel instead. Some real pistols have recoil springs around the barrel so it's not a completely unusual design, but the real CZ-75 has a regular spring and spring guide below the barrel.
A pistol of limited capacity that spits out shells every time you shoot isn't really the choice of a skirmisher, but the Marushin CZ-75 is not a complete joke in the performance department - of course considering the age. It shoots 0.2 gram BBs at around 200 fps with HFC134a, and is capable of putting shots into a palm-sized grouping from 5 meters. The slide action is surprisingly swift with a strong recoil spring, but the felt recoil is nothing to write home about because of light moving parts and the use of HFC134a. This pistol has no hop-up whatsoever, but the rear sight is quite high to extend the range by slight arcing of the BBs. (We wonder if the lack of hop-up on early models is the reason why Marushin puts two (sic) of them in their current models...)
They don't make them like they used to... No wait! In the summer of 2008 Marushin did announce that they are releasing another shell-ejecting GBB pistol, the Glock 21. The CZ-75 was a collector's item already 10 years ago, but perhaps there is a chance that these things are revived with new technology! And if you're into CZ's, you may want to jump on the few KSC models we still have left while they last.