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Indianapolis IN 46201
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The "Cyclone" On/Off Top Replacement for the Automag

From AKA/Leads Metal Products
Ravi Chopra, 1997

Cyclone on/off top

Anyone who's ever used a 68 Automag for any extended period of time has almost certainly experienced drop-off problems with rapid fire. Drop-off (also known as shoot-down and walk-back) is the condition where, under rapid fire, the 'gun starts to lose velocity after a number of shots. This occurs when the air chamber behind the bolt is not completely filled to regulated pressure between shots so subsequent shots are fired with low pressure, and therefore come out with low velocity.

The reason this happens is because of restrictions in the gas-path through the 'gun. The single most significant bottle-neck in the gas-path is the on/off valve. This valve lies immediately upstream of, and directs the gas flow to, the air chamber. The gas-path through the on/off runs through a part called the on/off top, a brass piece that fills most of the valve space and is supposed to direct the gas flow to the air chamber. The problem is that this part offers very little space for air to flow through it, and therefore significantly restricts the flow of gas through it.

The Cyclone on/off valve top seeks to correct this problem by replacing the on/off top with a less restrictive piece. The Cyclone is a stainless steel on/off valve top replacement with just barely enough metal to ensure that the on/off valve bottom is spaced out correctly. It has a thin disc at the top and bottom connected by two slim posts to space them apart. Large holes are drilled in the discs to allow passage of the on/off pin and to ensure free flow of air into the valve. The rest of the Cyclone is simple empty space so as not to restrict flow through the valve at all. In principle, the Cyclone is a good design, leaving mostly empty space in the on/off top area so as to provide an extremely low resistance path to the air chamber. On the other hand, the Cyclone is only a valve top replacement and therefore does not address the problem with the stock valve bottom which partially occludes the hole leading to the air chamber.

In testing the Cyclone, I addressed the two biggest reasons that people experience drop-off. The first is restriction of air flow through the on/off valve during rapid fire. The second, and probably most common, reason for drop-off is short-stroking. Short-stroking results from a person "riding" the trigger. That is to say, the person does not completely release the trigger between shots, preventing complete opening of the on/off valve and preventing complete filling of the air chamber between shots.

I used an Auto-Response trigger to test the flow-rate characteristics of the Cyclone. The Auto-Response is a complete grip-frame and trigger mechanism replacement which allows a 'mag to shoot on both the pull and release of the trigger. This has two advantages. First, it allowed me to shoot very fast. Second, it forced me to cycle the trigger completely so I knew that any drop-off was not the result of short-stroking. I tested my 68 Micromag equipped with an Auto-Response and the Cyclone. As with the stock valve and other modified on/off tops, the Cyclone did not fare particularly well in this test. After a few shots, the velocity rapidly dropped off and the 'gun hung up and stopped functioning entirely. Since the only valves that have successfully passed this test have been complete on/off replacements (like the Reactor), I can only conclude that there is a flaw in the stock valve design that mere on/off top replacement can not alleviate.

To test how the Cyclone handled short-stroking, I fired the 'gun over the chrono without completely releasing the trigger between shots (I intentionally severely short-stroked the trigger). It is in this area that the Cyclone stood head and shoulders above all other on/off valves I've tested. Where the stock valve allowed velocity drops of about 50 fps when short stroked, the Cyclone only allowed velocity dips in the 20-30 fps range. This is significantly better than any other on/off replacement (top or complete) I've ever tested.

The Cyclone follows a common trend in trying to alleviate drop-off in the Automag by providing a less restrictive on/off top. The Cyclone's design is sound and its construction is excellent. Though its performance in the Auto-Response test indicates that it is not the ultimate solution to the air-flow restriction problem in the Automag's on/off assembly, it's unmatched performance in the short-stroking test is really a better indication of it's value. From my own personal experiences, and from observations of other players shooting the Automag, I'm convinced that players most frequently run into drop-off problems as a result of short stroking. This is particularly true in the case of 'mags that have had trigger-jobs done to give them extremely short pulls and encourage the shooter to ride the trigger when rapid firing. The Cyclone's excellent alleviation of drop-off when short-stroked make it a particularly suitable selection for most players suffering these problems.

All material at this site is © Ravi Chopra, 1999