T&E: February 2000
By Al Paulson
Genius in Suppressor Design
The design of sound suppressors took a quantum jump forward on May 13, 1986, when the U.S. Patent Office awarded Patent Number 4588043 to Charles A. “Mickey” Finn. In my opinion, the three baffle designs covered by this patent represent the most significant achievement in sound suppression technology over the preceding three-quarters of a century. Not since Hiram P. Maxim’s Patent Number 916885 was awarded on March 30, 1909, had the field of silencer design seen such genius applied to the problem of stealthy shooting. Taking the time to understand how Finn’s innovative baffles work is a great way to jump well up the learning curve on how to effectively dampen the sound signatures of gunshots. In fact, one can make the argument that mastering the information in Finn’s patent will provide the moral equivalent of a Master’s Degree in sound suppression.
Much of the progress in the field of suppressor design throughout the late 1980s as well as the 1990s has been stimulated by analyzing the principals revealed by Finn’s work, and then applying those lessons in new ways. That, in a nutshell, is how progress in science and technology always works.
The easiest way to get your hands on Finn’s patent is to visit IBM’s Intellectual Property Network on the World Wide Web (the URL is http://www.patents.ibm.com). Once you’ve digested this patent, searching the database with key words such as “silencer” or “suppressor” or Boolean phrases such as “silencer + gun” or “suppressor + firearm” will reveal a number of additional patents worth studying if you are a serious student of suppressor design. Using a Boolean search phrase will help avoid a lot of extraneous hits related to automobile mufflers and silencers for air conditioners. But the cornerstone of such a quest for knowledge should be Finn’s ten-page Patent Number 4588043.
The patent describes three distinctly different baffle designs based upon a central concept—the slanted sidewall—which is defined as “a cylinder whose axis passes through the central axis of the sound suppressor at a predetermined angle so as to direct propulsion gases passing through the opening.” The slanted sidewall directs a gas jet diagonally across the gas stream following the bullet, deflecting a portion of that gas stream away from the central axis of the suppressor, where the gases can be slowed and cooled, robbing them of energy that would be perceived as sound. Four of the twelve figures in the patent are included here.
Figure 1 shows the preferred design of Finn’s Type 1 baffle (called the “first embodiment” in the patent, it has subsequently come to be known as the Type 1 baffle by suppressor cognoscenti). While this is a versatile design with a great deal of subtlety, it requires a fair amount of machining. I have seen simplified versions of the Type 1 baffle used for some applications. In fact, a photograph accompanying this discussion shows a Type 1 baffle simplified as much as possible; it’s just a flat disk with a slanted sidewall. Two noteworthy aspects of the preferred embodiment of the Type 1 baffle include the use of asymmetric surfaces to maximize turbulence and the use of geometry to enhance the effectiveness of the slanted sidewall. The Type 2 and Type 3 baffles also incorporate radial openings into the rear of the slanted sidewall (see Figures 2 and 3, respectively). These openings are designed to increase the diagonal gas jet formed by the slanted sidewall.
The preferred embodiment of the Type 3 baffle includes an integral conical spacer and a flat baffle. The baffle incorporates slots in the rear surface that communicate with an annular chamber inside the baffle. The annular chamber dumps gas into the rear of the slanted sidewall via three radial ports. A cut-off chord in the rear surface of the baffle (which is perpendicular to the aforementioned two slots) provides a large third pathway into the annular chamber inside the baffle.
The preferred embodiment of the Type 3 baffle also includes a mousehole at the wide part of the conical spacer (see Figure 4). This mousehole has several functions. It permits the flow of gasses from the coaxial expansion chamber (formed by the conical spacer) back into the central axis of the suppressor. And it releases gas pressure from the front of the coaxial chamber, which prevents the buildup of back pressure that would prevent more gas from entering the rear of the coaxial chamber.
While one can learn a great deal about the outstanding Type 3 baffle from the text and drawings of Finn’s patent, there is no substitute for seeing the actual object being described. Therefore, the photos accompanying this discussion provide details of the Type 3 baffle used in the Large Suppressor designed for the MP5SD-N. The Large Suppressor was manufactured by Heckler & Koch for the U.S. Navy under a licensing agreement from Qual-A-Tec in Oceanside, California. Heckler & Koch used a proportionately smaller but otherwise identical Type 3 baffle in the Small Suppressor, which was designed for the HK P9S pistol as well as the MP5-N and MP5K-N submachine guns. While the designs of HK’s Small and Large Suppressors are discussed in a two-part article that appeared in The Small Arms Review [see 2(4):28-32 and 2(5):28-31], photos illustrating the details of a Type 3 baffle as used by Heckler & Koch were not available at that time.
Note from the photos that the Type 3 baffle design used by Heckler & Koch moved the mousehole from the front edge (wide part) of the conical spacer to the rear (narrow part) of the conical spacer opposite the front edge of the slanted sidewall. Placing the mousehole here increases the efficiency of the slanted sidewall, directing its diagonal gas jet into the coaxial expansion chamber formed by the spacer.
Heckler and Koch began producing robust, accurate and quiet silencers based on Mickey Finn’s Type 3 baffle in 1986. The specific suppressor designs were developed by Finn’s company Qual-A-Tec and manufactured under at HK’s facilities at Chantilly and Sterling, Virginia. The photos of HK’s Small Suppressor accompanying this article were provided by Hays Parks, who was involved with the Navy’s development of an effective 9x19mm subsonic round in the 1980s based on a 147 grain projectile. The goal was to develop a 9x19mm cartridge that would provide an optimum mix of accuracy, incapacitation of the target, and lack of overpenetration. The latter criterion was important since the mission of certain elements within the Navy had been expanded to include in extremis missions such as counter-terrorism and hostage rescue. The HK P9S pistol and Small Suppressor were used during the course of this research program, which spawned the Winchester 147 grain JHP subsonic round that has stimulated the proliferation of 147 grain rounds in the marketplace.
The U.S. Navy is seldom seen as the originator of innovative developments in small-arms ammunition. But in the case of the 9x19mm JHP subsonic round, Navy innovation made a significant contribution not only to military technology, but to technology available to the law-enforcement community and private citizens as well. (The Navy’s development of this round is discussed at length in Silencer History and Performance, Volume 1; ISBN 0-87364-909-5). It is reasonable to assume that 147 grain JHP will play a major role wherever 9mm ammunition is used for decades to come. While the HK 9mm suppressors using Mickey Finn’s Type 3 baffle are now out of production, they remain in the Navy’s inventory, and they should provide service well into the future as well.
Most important of all, Mickey Finn’s innovative baffles and suppressor construction have fundamentally changed the field of silencer design. If one uses a yardstick based upon the number of practical and effective suppressors developed by other designers based directly or indirectly upon the principals revealed by a designer’s work, then one could make the case that Finn’s slanted sidewall baffles represent the most important contribution ever made to the field of sound suppressor design.
That may overstate the case only slightly, for Hiram P. Maxim provided the first commercially successful silencer designs, proving that gunshot noise could be reduced substantially by a simple, compact and practical device that could succeed in the marketplace. We might not be having this discussion at all without Maxim’s contributions. Furthermore, Maxim’s outstanding designs still work pretty well by modern standards even though they date back to the era of primitive canvas and wire biplanes.
When Finn turned his genius to suppressor design, the state of the art was not much different from World War II technology developed during the era of the radial engine. Finn’s work catapulted the field of suppressor design into the Space Age, providing a quantum jump in the state of the art and fundamentally changing the direction of subsequent developments. It is my contention that the contributions made by Hiram P. Maxim and Charles A. “Mickey” Finn to the field of suppressor design can best be described by the word “genius” since they have contributed “extraordinary creativity” to the field of suppressor design. That’s quite a legacy.
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