Paint - How It Works - The AutoMag

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How It Works - The AutoMag

Published Aug 1996
An Article by Mike Wallis

You have seen from my last two articles how two different types of semi's work. The blow forward action I'll describe this month I consider to be one of most elegant paintball gun designs on the market.

The only blow forward paintball gun on the market today is the 68 Auto-Mag. The Auto-Mag consists of four major components. The bolt assembly, the gas valve assembly, the trigger assembly and the gas regulator.

When a gas bottle is fitted the gun is ready to fire, no cocking of the action is required. The gas passes first through a gas regulator. (This regulator allows the pressure in the forward air chamber to be changed and thus alter the velocity of the gun. More pressure = more velocity.) The gas then passes through an on/off valve to the air chamber behind the bolt assembly. The bolt is held in the open position against this gas pressure by the trigger sear. The central pin of the bolt assembly sits against an o-ring like a cork in a bottle to seal the air chamber.

To fire the gun the trigger is now pulled. The trigger performs two functions using a pivoting sear lever. First it closes the on/off valve which consists of a pin, a two piece valve body and some o-rings. When the trigger is pulled the rear part of the sear lever pushes the pin in closing off the valve. As the valve is closed the front part of the pivoting sear lever has moved far enough downwards to release the bolt.

The central pin of the bolt assembly is now forced forward by the pressure in the air chamber. As the bolt moves forward it pushes a paintball into the barrel. Whilst this is happening the expanding gas is passing around the central bolt pin and is ported to the front of the bolt. When the bolt reaches its forward position the gas pressure behind the paintball is enough to propel it out of the barrel. The bolt is then returned to its open position by the now compressed main spring .

As the trigger is released the front part of the sear lever pivots up to re-engage the bolt whilst the rear part pivots down to re-open the on/off valve and allow the regulator to supply a measured amount of gas back into the air chamber. The gun is now ready to fire again.

A Custom AutoMag

As you can see this is a very simple elegant design. The only downside of the gun is that it is designed to operate using gas only. Because CO2 is stored as a liquid in the back bottle any of this liquid surging into the gun or condensing in the air chamber can cause velocity and functioning problems. Using an anti-syphon bottle and allowing it to warm after filling I'm told minimises these problems. On the plus side the gun is very gas efficient and gets at least 400 shots per 7oz tank.

If you get a chance to see the Auto-Mag video have a look. It covers the history and developement of the gun as well as fault finding.