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The "Cyclone" On/Off Top Replacement for the Automag

From AKA Design and Leads Metal Products

© Ravi Chopra, 1998

Anyone who has 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 at 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. Another problem is that the valve bottom partially occludes the hole leading forward to the air chamber.

The Cyclone is a replacement on/off valve top which seeks to correct this problem by offering a larger gas path through the on/off.


The Cyclone was designed as a replacement for the on/off valve top only. The stock valve bottom, piston, and seals are used throughout the rest of the on/off assembly. It is machined entirely from stainless steel and is nothing more than 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.

The Cyclone leaves mostly empty space in the on/off top area so as to provide an extremely low resistance path to the air chamber. I also like the use of stainless steel with something that really has so little material holding it together. 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 still partially occludes the hole leading to the air chamber.

As such, the Cyclone is a decent design which takes the opening of air-flow space in the valve top to an extreme. On the other hand, it doesn’t really break any new ground or address any of the other failings of the stock on/off design.

Design/Construction rating [3]


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. 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, 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 impressed me. Where the stock valve allowed velocity drops of about 50-60 fps when short stroked, the Cyclone only allowed velocity dips in the 20-30 fps range. This is a significant improvement over the stock, and quite a bit better than any other valve I’ve tried.

Performance/Versatility rating [3]


At an MSRP of $19.95, the Cyclone is almost double the price of most on/off top replacements. This is a lot of money for such a tiny piece of metal. The performance is good, but that and stainless steel construction hardly warrant this large of a premium.

AKA’s warranty protects you against manufacturing defects, which is really all you’d worry about with as simple a part as this anyhow.

Warranty/Price rating [2]

All material at this site is © Ravi Chopra, 1999