The Crosman 600 is a CO2 powered pellet pistol manufactured between 1960 and 1970. Unlike its contemporaries it was equipped with a unique mechanism that used some of the gas from each shot to actuate a shuttle mechanism that took a 0.22" lead pellet from the inline magazine and placed it in line with the rifled barrel at the moment of firing.
This particular example is a late model denoted by the plunger on the chamber cap used to puncture the 12 gram CO2 cartridge that powered the pistol. The wooden grips are aftermarket items.
The magazine follower can be cocked back into a notch allowing the 10 round magazine to be filled from the front.
Fully loaded magazine.
In the fired position, the shuttle is in line with the barrel. Cocking the hammer puts it in line with the magazine, allowing a pellet to feed. Once the trigger is pulled, the hammer simultaneously opens the valve momentarily while putting the shuttle in line with the barrel. Full video: https://youtu.be/1F7M3_zdBQA
The mechanism is seen here filmed at 1000 frames per second. The CO2 which escapes the valve not only propels the pellet down the barrel but also recocks the hammer which in turn returns the shuttle to the magazine feed position.
There is no seal around the shuttle, so in spite of it being a tight fit a visible amount of CO2 escapes around it. The pistol fires 14.3 grain pellets at a respectable 335 feet per second, sufficient for backyard plinking and for dealing with small pests at close range.
Viewed from above, note how the stack of pellets in the magazine temporarily moves rearwards at the moment of firing, as the domed head on the next pellet in line is forced out of the hollow skirt of the pellet about to be fired.
