This month I'm going to explain the operation of a closed bolt semi-auto. Two examples of this type are the Auto-cocker from Bud Orr and the Typhoon by Glenn Palmer. Now both of these guns are in fact converted pump guns. Having examined a Typhoon very closely I'll use this gun as an example for my explanation.
The Typhoon is based on the Sheridan KP3 series pump action paintball rifle. So I have only shown the semi-auto parts in the diagram.
As can be seen from the diagram the Typhoon consists of a pump gun with added low pressure pneumatic components. There are three major components, a double action pneumatic cylinder, a 4 way control valve and a low pressure regulator.
Because the CO2 gas is stored at high pressure a regulator is required to lower the gas pressure to around 60 to 80 PSI for use by the auto-cocking system. This low pressure gas is then switched by the 4 way valve to either end of the pneumatic cylinder to open and close the action.
This is how it works. Assuming we have fitted a gas bottle and filled the hopper with paintballs all we need to do to cock the gun is pull the trigger and release it. Apart from its normal job of releasing the hammer to fire the gun the trigger is also connected by a linkage to the gas valve. When the trigger is pulled right back this depresses the gas valve. The valve then ports gas to the back of the pneumatic cylinder causing the cylinder rod to extend, open the bolt and cock the action. A paintball then falls into the breech. When the trigger is released the gas valve moves up switching the gas pressure from the rear to the front of the pneumatic cylinder. The cylinder rod now reverses and returns the bolt to the closed position. The gun is now ready to fire.
To fire we pull the trigger again. This time as we pull the trigger the hammer is released firing the gun. As we continue to pull the trigger back past the point where the hammer was released the gas valve is again depressed by the trigger linkage. This repeats the above cocking sequence. Now every time we pull the trigger the gun fires and then cycles the pneumatic cylinder to re-cock and load the action.
Glenn's First Semi, "Camille".
This system works very well but it is much more complicated than an open bolt semi-auto. Because besides adjusting the velocity, you must also adjust the low pressure regulator and occasionally the trigger linkage for correct functioning of the pneumatics.
The principle of operation is simple isn't it. In my next article I'm going to tackle a blow-forward semi-auto the Auto-Mag 'til then keep painting.
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