In 1943, Russell S. Robinson started the design and development of what many would consider to be a proper machine pistol, i.e. a pistol that would fire automatically yet having recoil so low as to be controllable in this mode of fire. The Model 11 is not a true Constant Reaction gun in which the barrel, extension and bolt are used to pre-absorb recoil, but uses the slide or jacket to provide all of the inertia. This is a unique approach to solving the problems of firing in full automatic with a weapon the size of a Colt M1911A1.

The Model 11 employs two distinct principles: firstly to smooth out the rearward recoil kick and secondly, to smooth out the torque impact resulting from spinning the projectile to about 1,500 rpm which disturbs aim in a light hand held weapon. The second principle involves rotating the barrel while the slide is moving forward, with the rotation of the barrel in the same direction as the spinning projectile. While we will examine in detail the operation and design of the Model 11 later on, we will first take a look into the history of its development, and what role Russ Robinson had in mind for the Model 11 when designing and developing it. It turns out that this was the role of a Personal Defense Weapon (PDW) long before the concept of a PDW came into vogue.

Inspiration from the Gatenby .45

In 1942, an Australian named Gatenby submitted to the Australian Army Inventions Directorate (A.I.D.) for evaluation a very unusual .45 caliber Machine Carbine/Pistol. Intrigued, the A.I.D. sought a version in 9mm for evaluation and Robinson, at the time involved in firing-range tests of his Model 5 Cal. .50 machine gun, was contracted by the A.I.D. to design a version in 9mm.

The Gatenby gun fed rearward out of the magazine, with a fixed buttress on the pistol grip having a fixed firing pin. A sliding barrel was used with about 1.5 inches of movement. When a round was chambered and fired, the force of engraving and friction of the bullet in the rifling carried the barrel forward against a stiff spring, with a spring-biased extractor in the buttress holding the fired case against the breech face. A fixed ejector spun the empty case off the breech face after the barrel had moved forward about 1.25 inches. Hitting a forward stop at its forward limit of movement, the barrel returned rearward, with a fixed finger under the barrel striking the point of the next cartridge in the magazine. This thrust the cartridge rearward against a ramp that guided it upwards, and, simultaneously, the recoiling barrel pushed the point of the cartridge upward and chambered.

Problems with feeding reliably due to insufficient support of the cartridge while the barrel moved rearward, as well as the heavy recoil, made the Gatenby very difficult to control in a full-auto burst mode. The heavy recoil was due to a combination of the simultaneous recoil shock of ignition and the shock of the returning barrel hitting the fixed breech face.

Robinson designed two variants of the 9mm Gatenby, these being known as the Models 8 and 10. While the Gatenby did not continue any further, it did impress Robinson with some aspects of the design. He initially considered that the Constant Reaction principle was only applicable to .30 caliber and larger, but the Gatenby concept inspired him to apply a variation of the principle to a light weight gun. He felt that a cyclic rate of 600 rpm, with continuous recoil of 5.2 pounds, with the recoil varying about 1.75 pounds, would result in an accurate one-hand held machine pistol. The end result was the S.R. Model 11 9mm Machine Pistol.

Development and design of the Model 11

Conceived in early 1943, the drawings were finally completed by March 1944, and construction was approved in November 1944. Major modifications to the design were necessary due to Russ Robinson’s failure to realize that when the slide struck the barrel via the chambered case, substantial energy was lost in getting the six ounce barrel up to slide speed. As a result of this failure, six ounces had to be added to the slide weight at the rear to compensate. These modifications and redesign were finished by mid February 1945. By early September 1945, major components had been fabricated at the Small Arms Factory (SAF), Lithgow and the prototype gun had fired some 1600 rounds in tests.

The S.R. Model 11 9mm Machine Pistol was designed to initially meet some 13 specifications laid down in 1943 following the advice and assistance of Major J.E.M. Hall, then chief of the Army Small Arms Branch, Directorate of Artillery. One requirement that could not be met was the weight, as the slide alone had to weigh one pound. Additional recommendations and suggestions were made by Australian Army and R.A.A.F. service personnel returning from fighting overseas and later by the Canadians. In this revised list of specifications, numbering 24 in total, the weight was increased.

While some of the 24 specifications laid down have been examined in an article from the now defunct Fighting Firearms, (Summer 1996, Constant Reaction Guns II), let us look again at some of the more interesting. These are as follows:

1. Cyclic Rate of 500-600 rpm;
2. Weight not to exceed 2.5 pounds;
3. Provision for automatic ejection of empty magazine from gun;
4. Safety and fire-selection controls must be conveniently located and designed for immediate operation by right and left trigger finger only;
5. Recoil force to be smoothed out to permit accurate auto or semi-auto fire single handed;
6. Except for pushing home successive magazines, no handling or operational function to require a second hand;
7. The action to be kept in a cocked mode upon termination of burst fire as well as ejection of the magazine; and
8. Magazines to be made as expendable as possible.

Some of these requirements and features had never been seen before such as the automatic ejection of magazines when empty. Alternative feed systems were mentioned in place of the magazine. For example, a flexible feed system was proposed feeding through the pistol grip though nothing came about from this proposal. The auto-ejection of empty magazines, coupled with the retention of the gun in a fully cocked position, allowed for a very short time break in firing estimated to be about 0.5 second. The only movement required to re-commence firing was the pushing home of the new magazine. This feature resulted from advice from Australian soldiers fighting in the jungles of New Guinea.

During a trip to Canada, on the way home from the UK in 1945, Russ Robinson visited Small Arms Ltd. and John Inglis Co., Ltd., the latter being manufacturers of the GP35 Pistol and the BREN. Both of these manufacturers expressed a great deal of interest in the Model 11. Colonel Jolley, the Manager at Small Arms Ltd., suggested that a light holster or combination holster/shoulder stock be developed, similar to that of the Mauser Broomhandle and the FN GP35, to enhance the effective range of the Model 11. However, a simple tubular telescoping stock was eventually designed and manufactured, which was attached to the pistol via a tapped hole in the frame. The holster ended up being made of canvas with a separate slip to accommodate the telescoping stock.

When Russ Robinson returned to the UK in the latter part of 1945, he took with him a number of S.R. Model 11 Machine Pistols complete with tubular stocks and canvas holsters. These guns were then later modified after tests in 1946. While these tests were carried out by the UK Ordnance Board, in another ironic twist, the trial report was signed by Major J.E.M. Hall, the Australian Army officer whose advice led to specifications for a 9mm machine pistol being laid down in Australia and ultimately resulted in the development of the S.R. Model 11. Major Hall had been transferred to the UK to work on various small arms projects, and was in charge of a design team working on the .280 rifle project.

The S.R. Model 11, in its initial form, resembled a normal semi-automatic pistol, with the exception of the grooves machined into the exterior of the long barrel. Conducting further research for this article proved the old adage that “hands-on” research provides new insights into a subject. Up until now, it was commonly believed that only four S.R. Model 11 9mm Machine Pistols, including the prototype, were manufactured at SAF Lithgow, though there were some references in official files to a fifth gun being manufactured for spares only. The fifth gun was recently discovered in an official collection in Australia, and it is in an unmodified condition, unlike the other existing Model 11 guns that were modified in England. With the number 5 marked on the slide, it appears that this gun was assembled at SAF Lithgow, and somehow ended up in this official collection along with a modified Model 11 that is now in another official collection within Australia. This discovery allows us to view for the first time what the original Model 11 looked like prior to being modified in England. The markings on this fifth gun match those shown in the original drawings, and the differences between the unmodified and modified specimens are quite striking. The most obvious difference is the extended tang on the pistol grip while the modified slide is longer, heavier and has different markings.

Trials and Tests in the UK

In 1946, the Model 11 underwent sand and mud tests at Enfield held in conjunction with accuracy tests. Major Hall ran these trials, and the accuracy tests produced some interesting results. The Model 11 was found to be more accurate in full-auto fire than the Sten Mk V and the Polish-designed Machine Carbine Experimental Model (MCEM), which is believed to be the MCEM 2. Both the Sten Mk V and the MCEM 2 were used as controls in both the accuracy and sand/mud tests. The accuracy tests showed that the Model 11 was not as accurate as the two control guns in semi-auto fire. The sand and mud tests showed some problems with the change lever and also clearance between the magazine and the housing had to be increased slightly.

Russ Robinson’s work for the British at the time concentrated more on machine guns so the Model 11 received only spasmodic attention to improve the design. After carrying out their initial tests, the Ordnance Board (OB) felt that if it looked like a pistol, was carried like a pistol in a holster, was used like a pistol, and its weight was like a pistol, then it should shoot like a pistol in semi-auto fire. The OB advised Robinson that the gun should be re-designed so that it would provide accurate semi-auto fire but at the same time maintain the accuracy levels achieved with full-auto fire. This was easier said than done, as it would require a major re-design of the Model 11 to allow semi-auto fire from a front sear position, and a change from a fixed firing pin to a more conventional floating firing pin. Robinson looked at this, and this re-design was known as the Model 16. Unfortunately, the Model 16 was never built, with the exception of some firing fixtures.

In 1948, Robinson experimented with heavy alloy metals to try and increase the weight of the slide without making the gun more bulky. Using an alloy made by General Electric Company known as “Heavy Alloy”, which was 50% heavier than steel, new slides were manufactured which were slightly thicker and longer than the original slides. Modifications to the frame included welding an extension to the tang of the frame. Slides were manufactured and fitted to the Model 11 guns that Robinson had brought with him from Australia, and it was envisaged that further tests would result in a total re-design and lead to further manufacture. These tests never occurred because Russ Robinson moved to the United States, and the British had by then adopted the Patchett submachine gun.

Operation of the Model 11

The S.R. Model 11 is a very simple gun with a total of just 22 parts including checkered wooden grips and screws. It has a floating barrel that is the secret of the low recoil force in the various machine pistols designed by Russ Robinson. The floating barrel enabled the forward momentum of the slide to be fully harnessed to pre-absorb almost half of the recoil. The automatic ejection of the magazine is accomplished by an ejection system that is triggered when the rising magazine follower strikes the magazine retainer when it rises to the top of the magazine. The release of the magazine retainer permits the magazine ejector to thrust the magazine downward and out of the butt. At the same time, a heel on the ejector rises and holds the slide slightly to the rear of the sear position. When a loaded magazine is thrust in place, the magazine ejector is rocked upward by the rear wall of the magazine and its heel is withdrawn allowing the slide to move forward .025 inches to rear (cocked) position, and the gun is ready to fire.

When the trigger is pressed, the slide is accelerated forward by the driving spring, the rear end of which bears rearward against the barrel and holds it against its rear stop. As the slide moves forward, it forces the barrel to rotate at a fairly constant angular speed by the grooves in the slide nut engaging the external grooves on the barrel. By the time the slide reaches forward or firing position, the rotational energy of the barrel is about one half that of the fired bullet. When the fixed firing pin of the slide strikes the primer and ignites the charge, a very slight delay occurs while combustion fully develops. At the speed the slide is moving, it wants to move about .030 inches before the recoil is sufficient to arrest and then reverse the motion of the slide. Because of this delay, the slide is arrested in 9mm weapons not by recoil, but by the slide striking the fixed barrel and frame via the fully chambered cartridge case. The greater part of the forward energy of the slide is dispersed into the frame or pistol grip. In order to make the forward energy or movement of the slide fully available to pre-absorb almost one half of the recoil, the barrel of the Model 11 is allowed to slide forward with the slide.

As the bullet leaves the muzzle it has about twice the rotational energy as that of the rotating barrel, so the barrel rotation is arrested and reversed by the rotating bullet. But as the slide moves rearward, the barrel’s rotation is decelerated so that the decelerating torque is in the same sense as the accelerating torque when the slide is going forward. Thus the heavy torque impulse to spin the bullet is replaced by a continuous very small torque which is applied throughout the entire cycle of fire, and which is too small to affect aim during automatic firing.

Each cycle of fire in the Model 11 is followed by a small cushioned blow of the slide against the rear buffer of the pistol grip, which represents a reserve of energy to provide for elevated firing or firing under foul conditions. The blows against the buffer can be felt, but they are very small compared with usual 9mm recoil. The Model 11 was not a true constant reaction gun but it employed a combination of the constant reaction principle with rotating the barrel in the direction of projectile spin, and recoil was reduced greatly by this unique combination. Robinson found that the rapid firing of the gun produced a succession of reactive torque impacts upon the gun, thus affecting accuracy. There is a tendency for such a firearm to react with non-axial twisting pulses. And if these impacts could be cushioned so that the impact is applied to the gun over a long time, then the effects on accuracy due to imparting bullet spin in a very light weapon can be virtually eliminated. The selector mechanism used with the Model 11 is a simple three-position system. The selector is ambidextrous and can be used with either trigger finger. The full-auto position is when the selector lever is fully up and parallel with the slide. Moving the selector lever downwards about 20 degrees clicks it into semi-auto position; and in the safe position the selector lever is fully down and blocking access to the trigger while internally locking the sear.

Ejection of empty cases is via an ejection port in the top of the slide. With the exception of a magazine change, all operations necessary to use the gun require only one hand, thus meeting a major specification laid down back in Australia. Magazine capacity was 14 rounds for the initial holster friendly magazine, and 30 for the subsequent magazines.

The Model 11 U.S. Patent

In 1970, Russ Robinson applied for a U.S. Patent on the concepts he developed with the original Model 11, with the U.S. Patent Office granting the patent on June 12, 1973. The patent disclosed two different approaches to the original ideas as used in the original Model 11, and the additional approach is worthy of some discussion.

The original approach is disclosed though with some differences from the actual Model 11. Rather than have the recoil spring positioned around the barrel as in the actual Model 11, the patent disclosed having the recoil spring being positioned below the barrel. It is believed that this approach was used in the design of the later Model 16. Another difference disclosed in the patent involved the addition of a ring of a resilient material, such as synthetic rubber, to the forward bearing surface between the slide and the external helical grooves in the barrel. This feature was included specifically for the Model 11 as a “…type of firearm…in which a short dwell time occurs in the movement of the slide after it has completed its counter recoil movement and before it receives its recoil movement…”

The alternate embodiment disclosed in the patent was for a firearm with a rotating barrel and two bearings, one at the front of the barrel and the other at the rear, the rear bearing being positioned in the receiver of the firearm. The design allowed for the barrel to be restrained from longitudinal movement, but allowed for the unobstructed rotation of the barrel within the receiver and within the constraints of the two bearings. The receiver included a saddle at the front of the receiver with a friction clip or clamp as a part of the saddle. The friction clip or clamp utilized a simple tension screw that was threaded into a threaded hole in the saddle.

Tightening the screw increased the clamping action of the friction clip and increased the torque resisting the rotation of the barrel with respect to the receiver. When correctly adjusted, the firing of a shot resulted in the barrel being reactively spun by the projectile to an angular velocity in which its angular momentum, less the losses generated by friction, was equal to but opposite to that imparted by the projectile. This resulted in the clamping torque being applied to the barrel so that the barrel was brought to a rest in a period considerably longer than the period of projectile travel in the barrel. Reduction of the torque level and its application to the receiver resulted in the cushioning of the reactive torque impact on the receiver.

Research into the various guns developed by Russ Robinson has failed to find any particular firearm that utilized this version of the invention, and it is believed that this approach was a theoretical design and concept that was never proven in an actual firearm.

The Model 11/16 as a PDW

Examination of personal and official files has shown that, if the problem of semi-auto fire could have been solved quickly, the British would have seriously considered adopting the Robinson gun for use in a multi-purpose role replacing the pistol and the machine carbine. This is the role that Russ Robinson envisioned right from the start for the Model 11, a role now known as a PDW or Personal Defense Weapon.

Initially, the S.R. Model 11 was designed as a standard holster weapon for officers, NCOs, drivers, jungle artillerymen and such, but the fact that it was so light and able to be used with one hand opened up many possibilities for use by other military personnel. Robinson felt that a 2.5-pound 9mm carbine that is normally carried in a holster would be extremely valuable for street and jungle fighting, and night operations. He envisioned that, combining the use of such a weapon with the standard infantry rifle, there would appear to be little requirement for the orthodox type carbine.

The OB was of the opinion that a combination of the self-loading pistol and the machine carbine would be very interesting, but weight would be a major factor. The weight would have to compare favorably with other self-loading pistols for it to be seriously considered. While the weight factor was easily achieved, it was the semi-auto requirement that was awkward to achieve without a major re-design of the gun.

The Model 16 still kept many of the highly desirable features of the Model 11, including one-handed operation, ejection of empty magazines, selective-fire capability, and most critical, a projected weight of 2 pounds 4 ounces unloaded.

The story of the Model 11 finished when Russ Robinson moved to the US, and no further development of the Model 11 or Model 16 occurred. However the specifications laid down for the Model 11 so many years ago mirror, in many aspects, current requirements and operational roles for a PDW/OPW.

Perhaps we do need to reflect upon what has occurred in the past, take heed, and start to break out of the circle that continues in small arms design. Many of today’s so-called advances in small arms have their roots in the past, when lessons were not heeded. Just imagine what would have happened if the British had adopted the Model 11 or 16. Much time, money and effort would not be expended today trying to create a solution that may already exist. In a conversation with Russ Robinson in 1995, he indicated that he would be glad to undertake the design of an improved Model 16 if a firm requirement arose from a responsible source. Regrettably, following his passing away in late 1998, this will not occur. But, perhaps we may still see such a gun incorporating Russ Robinson’s concepts and ideas.

The author wishes to acknowledge the assistance of the following: Australian Army Engineering Agency (A.A.E.A.), (formerly A.T.E.A., Army Technical & Engineering Agency), Maribyrnong, Victoria, Australia; MOD Pattern Room, Nottingham, United Kingdom; the late Mr. Herb Woodend, and the late Mr. Russell S. Robinson in the preparation of this article. Their assistance is gratefully appreciated.

by N.R. Parker

If you become seriously interested in the guns you own, and are interested enough to start researching the history of a particular gun such as who designed or invented it, sooner or later you may want to see if there are any patents granted by the United States Patent & Trademark Office (USPTO) that relate to the particular gun. This article is intended as a guide to finding any patents that may have been granted by the USPTO, the classification systems used, and conducting a search on the USPTO Web Site.

There are a number of ways to see if a patent has ever been granted for a gun, though doing it via the USPTO web site is probably the easiest and the quickest. Bear in mind that there are unfortunately restrictions on what you can search, and how you can search, and when one takes into account that the USPTO has granted over 6.5 million patents since 1790, one of the main problems for the USPTO is the size of the database. Currently it is about 4 terabytes large, and full search capabilities are restricted to patents granted from 1976 onwards. This restriction does affect the patent searcher, especially if they are interested in firearms from the pre-20th century through to 1976 era. However, before we get too deeply involved, let’s look at some basics.

Patent Classifications

The USPTO uses its own unique patent classification system, and while there is another more widely used system, called the International Patent Classification (IPC) which is used outside of the US, we won’t examine the IPC system for now. There are Concordances available that give an IPC to USPTO and USPTO to IPC equivalent classifications and checking these can be helpful in finding foreign patents, as foreign countries use the IPC system extensively. As the US system is the one we’re interested in, let’s probe a little deeper into the USPTO patent classification system.

US Patents are placed into over 400 different classes, depending upon the patented item. There are 4 main classes that are of interest for our purposes and these are Classes 42, 86, 89, and 102. These classes are Firearms (Class 42), Ammunition and Explosive Charge Making (Class 86), Ordnance (Class 89), and Ammunition and Explosives (Class 102). There are other classes that are also of related interest including Class 124 (Mechanical Guns and Projectors). As the four main classes 42, 86, 89 and 102 are of most interest to us, let’s look at the USPTO class definitions.

The following definitions are extracted from the USPTO Manual of Classification.

CLASS 42 FIREARMS – CLASS DEFINITION

This class includes all the portable firearms, i.e., those which are supported by hand when operated, such as shoulder guns, pistols, toy firearms and cane guns, except the automatic or explosion-operated firearms. This class also has such firearms combined with cleaners, entrenching devices, bayonets, and other cutters (including specifically pistol-swords). The following devices are likewise found here either, per se, or in combination with the firearm; ram rods, gun-rests and some body supported arm rests.

CLASS 86 AMMUNITION AND EXPLOSIVES MAKING – CLASS DEFINITION

Instruments and processes peculiarly adapted for making fixed ammunition, including percussion caps, cartridges, or other explosive charges for firearms or ordnance, pyrotechnic devices, blasting charges, etc.

CLASS 89 ORDNANCE – CLASS DEFINITION

This class includes all guns adapted to be mounted or supported otherwise than by hand, all explosion-operated guns including hand and shoulder firearms, bomb dropping devices, and those gun combinations and sub-combinations which are not provided for in other classes including mounts, supports, carriages, loading and hoisting mechanisms, shields.

CLASS 102 AMMUNITION AND EXPLOSIVES – CLASS DEFINITION

This is the residual class for ammunition propelled by explosives and explosive methods or means which includes:

Missile, blasting means, payload, pyrotechnic, gun ammunition and/or miscellaneous explosive means. Gun barrel cleaning means which are propelled through the barrel by explosive or fluid under high pressure. Fluid under high pressure, other then chemical reaction, which escape very rapidly. Material which burns or combusts which is intended to be projected, dropped, thrown, or propelled is proper for the class. (1) By releasing a combustion material to the atmosphere, e.g., gas, incendiary shell, grenade, etc. (2) by generating heat to damage an object, e.g., thermite means. Sub-combinations peculiar to the class which are not classified in other classes, e.g., cartridge case, primer igniter, fuse, sabot, rifling band, wad, propellant form, etc. Dummy, practice, drill, training ammunition, etc., is classified with the conventional ammunition.

All of these classes are sub-divided into sub-classes, and the Manual of Classification used by the USPTO is always under revision.

An important point to remember is that all US patents, regardless of their age, are listed under their current classification on the USPTO Web Site. It is highly likely that, due to the revision of the classification system over time, the current classification may not be the classification originally given to the patent when granted.

For this reason, it is important to check the Manual of Classification as an initial step if checking by classification rather than by other means, such as the inventor’s name. If we don’t know the USPTO classification, we can search by description which will give us the class, and sub-class we are looking for, and once we have the class or sub-class, we can go from there.

Patent Databases at the USPTO Web Site

The USPTO web site provides searching by a number of different search criteria, and these are the quick, advanced and patent number searches. There are two databases that may be searched, and these are the Full-text since 1976 database, and the Full-page images since 1790 database.

Another database that may also be searched is that of Patent Applications which have been published since March 15, 2001. We will discuss the Patent Application database later, as there are special criteria that apply to this database.

The Full-text database allows you to search by some 30 different search fields, ranging from Title and Date through to Name of Inventor, US Classification, International Classification, and through to Claims and Description. The Full-text database also allows searching by certain time periods, and this is from 1976 onwards. This helps when narrowing down search criteria. When displayed, a list of patents granted post 1976 display the patent number and the title of the patent.

The Full-page Image database basically allows you to search by US classification, number or date only. When a list of patents granted prior to 1976 are generated by a search, all that is displayed is the patent number and the class or classes under which the patent is classified.

We are restricted to 1976 and onwards for full-text search, and this includes the name of the inventor or the name of the assignee if the patent is assigned to a firm or if the rights of the patent were assigned to another party or person or company. It is highly unlikely that the full-text search for pre-1976 US patents will change in the future, but for the present, it does restrict doing simple searches. There are a number of ways to get around this restriction, though it usually means checking patents individually to see if any patents listed under a certain class were granted to a particular person or company.

Another database that is searchable is that of Patent Applications. Since March 15, 2001 the USPTO has published Patent Applications. While in foreign countries patent applications have been published some eighteen months after application, until recently patent applications have been kept from public eyes due to US patent laws. Currently, there are a number of reasons to exempt a patent application from publication with the main reason requiring the applicants to submit a signed form with the patent application requesting non-publication of the patent application because there will be no filing of an application in a foreign country. This restricts publication until the patent has been granted. However, if no such request is submitted then the patent application is published. Many applicants do not seek publication for obvious reasons. These include commercial reasons, and if you have a lot of time, effort and money invested in an invention, why let the competition know what you’re doing? Intellectual property rights, such as patents, are valuable and many companies will go to extreme measures to ensure protection of their intellectual property. The Patent Application database is a full-text database and the same rules apply to searching as for post-1976 patents, with the exception that the database is limited to post March 15, 2001 for the date.

No matter what database is used to search; the patent numbers displayed are simply clicked on to allow viewing of the patent, either in full-text version or in full-page images. Viewing US patents does require some software that is downloadable from the USPTO web site via a link or by simply clicking on a URL.

Patent Viewing Software, Associated Software Problems and Access Controls

All the US patents require a file viewer to allow for correct downloading, viewing and printing of the patent in question. The patent files are TIFF file format, but not your normal TIFF file. The TIFF file viewer must specifically display TIFF files using ITU T.6 or CCITT Group (G4) compression. This means that you must use a plug-in to your browser to allow viewing of the patent images, and unfortunately there is a limited number of plug-ins that will permit this, and this is dependent upon the operating system of your PC.

For the Apple Macintosh, Apple’s freely distributed QuickTime version 4.1 or later will allow viewing, but does not provide printing capability. It is available from the Apple Web site at http://www.apple.com/software/.

For Windows system PC’s, the only free, unlimited time TIFF image viewers offering full-size, unimpeded patent viewing and printing unimpeded by any advertising on Windows x86 PCs are AlternaTIFF: http://www.alternatiff.com (tested on Internet Explorer, Netscape & Opera), InterneTIFF: http://www.innomage.com/inteneTIFF.htm (tested on IE & Netscape). For Linux, a plug-in called “Plugger” works nicely with Netscape Communicator. It is available at http://fredik.hubbe.net/plugger.html.

AlternaTIFF is a web browser add-on (ActiveX control or plug-in) and while it is free to use, it must be registered before it can be used to view images. If you use Netscape, Opera or another web browser, AlternaTIFF is available as a standard plug-in. If you use Internet Explorer 4.x and higher, it is available as an ActiveX control with auto install or as a downloadable ZIP file.

InterneTIFF consists of the viewer for Internet based TIFF images and innoVUE which is a viewer for locally saved TIFF images, and both of these viewers are bundled together when you download InterneTIFF. InterneTIFF works with IE 5.1, SP2, 5.5 and 6+ and Netscape Navigator, Communicator, Netscape6, Netscape7, Mozilla and Opera5+.

If there are any problems with either of these programs, check or read the FAQs on the respective web sites.

Once you have downloaded, installed the software and re-booted your PC, you are then able to view, print and save the patent TIFF files.

There are a number of problems associated with some of the software and downloading patent images, and the main one is that with AlternaTIFF, you are restricted to downloading the patent pages one at a time. With the full version of InterneTIFF, (check the web site for the current price), one can download, print or save the whole patent at once, without having to wait for individual pages to download. The free version, which allows for a 5-day evaluation during which you get to try all of the features, then reverts to printing, saving and viewing of each page. However, if you are prepared to download or print out the patent page by page, then use AlternaTIFF.

There is one other catch in using these programs. With AlternaTIFF, if you use your browser to view locally saved TIFF files, your browser may open the TIFF file with AlternaTIFF, but it is not as reliable as using a proper graphics application rather than a plug-in. With InterneTIFF, if you view locally saved TIFF files, you will use innoVUE, which is the file viewer for local TIFF files, and this means that all TIFF files on your PC will be opened by innoVUE. By default, your locally saved TIFF files are associated with innoVUE, and if you want to prevent innoVUE from opening your local TIFF files, you need to associate your TIFF files with a different application. You will have to use a graphics file viewer program such as Adobe PhotoShop or JASC’s Paint Shop Pro to open all TIFF files, including those which use the LZW file compression technique. Please remember this if you intend to download, store or print out a lot of US patents. If you want to be able to open a TIFF file directly and have it automatically open in a graphics application, you need to make sure TIFF files are associated with that application.

One way to associate files is to carefully follow these instructions:

1. Use Windows Explorer to locate any TIFF file on your computer, and select it (left-click).
2. Hold down the Shift key while you right-click on it.
3. Choose “Open With” from the menu.
4. Select your application from the list, or if it’s not listed, press “Other” to locate it.
5. Make sure “Always use this application…” is checked.
6. Press “OK”.

From now on, you should be able to view TIFF files by double clicking on them. (At least until you install some other application that changes your file associations again).

There is a warning from the USPTO that needs to be discussed here before we progress any further. The USPTO will not tolerate mass logins to their servers, with the subsequent mass downloading of patents. Individuals, companies, IP addresses, or blocks of IP addresses who, in effect, deny service to the general public by generating unusually high numbers (1000 or more) of daily database accesses (searches, pages, or hits), whether generated manually or in an automated fashion, may be denied access to these servers without notice. There are a specific number of users allowed at any one time, and as access, searching, downloading and printing is free via the web site, don’t abuse this access. The information available is a treasure trove, and there are commercial sites that charge quite high prices to do exactly what you can do for free at the USPTO web site. Abusing this facility will result in restricting or blocking your access. Conducting a patent search at the USPTO Web Site First thing we need to do is to download and install the appropriate software to view any patents available from the USPTO Web Site. As most people will be using a PC rather than an Apple Macintosh, initially I would suggest downloading the AlternaTIFF software from the following URL: http://www.alternatiff.com/

As stated above, this allows one to have free, unlimited patent viewing and printing from the USPTO Web Site. Once you have had some experience with searching, downloading, and viewing, I would suggest that you try the InterneTIFF software, and then purchase the full version if you intend doing extensive searches. The full version has some very good features for downloading, saving and printing patents. After downloading and installing the AlternaTIFF software, and connecting to the Internet through your ISP, go to the following URL: http://www.uspto.gov

As there are a number of different ways to search the patent databases, we will start with the following method, which also gives us an indication of the various sub-classes within a classification. We will look at other methods later on. So, what are we looking for? Is it in the firearms class, the ordnance class or the ammunition class? As an example, let’s assume it deals with automatic guns, and this places it in the ordnance class, this being class 89. Let’s go to the following URL: http://www.uspto.gov/go/classification

Next step is to check the actual class itself, so we click on the Class Numbers and Titles and that will take us to the following Web Page and URL. http://www.uspto.gov/go/classification/selectnumwithtitle.htm

We then scroll down to the class number, select the actual Class Number and Title, in this case 89, click “GO”, and the following Web Page and URL will be displayed.

When this is displayed in your browser, it will display the entire breakdown of the class and sub-classes within Class 89, and from this we can go to the particular sub-class we are interested in searching. To the left of every class or sub-class is an icon, which is a little white P in a red box. Clicking on this icon will result in a list of all US patents granted in the particular class or sub-class selected. This is one of the fastest ways to get a list of all US patents granted in that particular class or sub-class. If there are more than 50 patents in the class or sub-class, the patents will be displayed in a list of 50 patents per list, starting with the most recently issued patent and going through to the oldest patent issued for the sub-class. To check older patents will require clicking on the “Next List” box at the bottom of the page.

Patents with full-text search capability will be displayed with the patent number and patent title while patents granted prior to 1976 will display only the patent number and patent classification and sub-class(es) if classified in more than one sub-class.

Once we become familiar with the four main classes relating to firearms, and the sub-classes associated with the main classes, we can move on to searching with specific search fields in the full text database.

Searching the Full-Text Database

The Full-Text Database is a database that contains U.S. patents granted post-1976, and the database is capable of being searched by a number of specific fields. There are 30 specific fields by which the database may be searched, and these range from title, patent number, inventor, assignee, country, through to claim(s) and description/specification. You are even able to search for specific words within the description/specification field. To go to the Full-Text search page, enter the following URL for the Quick Search or Boolean Search Web Page: http://patft.uspto.gov/netahtml/search-bool.html

This will also give one-click access to other search pages such as the Advanced and Patent Number search pages as well as help files and searching by patent classification.

This page presents you with two terms and two fields that will allow you to search, and it is not necessary to enter all four items. You may also use the Boolean terms “ and”, “or”, and “and/not” to be more specific about the patents one is searching. Unless I am doing a search that needs to be very specific in the terms and the fields, I usually only enter one term and one field, and for what I am usually searching for, the Quick Search or Boolean Search page is the search page that I use most frequently.

The USPTO web site has extensive on-line help files for greater in-depth searching, such as that offered in the Advanced Search page, and explanations about the navigational icons used on the web site. If you intend to do a lot of searching, then spend some time and go through the help files as they explain more in far greater detail about patent searching than I am able to explain in this brief coverage. Once you get to know your way around the USPTO web site, most of the URLs listed here are available through one-click buttons.

Searching the Patent Application Database

Most of what has already been explained applies to searching the Patent Application Database with two exceptions. This Database covers the time period from year 2001 through to the present year, and the patent applications listed are only those where the applicant has not requested non-publication of the patent application. Patent applications subject to the non-disclosure request are only published when the patent is granted. If the patent is not granted, then the patent application is not available for examination by the public.

Other Methods of Patent Searching

There are a number of other methods of patent searching, and the most useful method basically involves spending some time at a library, but this may not be your local library. The USPTO has a program whereby libraries across the USA become part of the Patent and Trademark Depository Library (PTDL) Program. This program has been in place since 1871, and there are many libraries, both public and university, that are members of the PTDL Program. A full list of libraries is available at the following URL: http://www.uspto.gov/web/offices/ac/ido/ptdl/ptdlib_1.html

Using a PTDL is most useful when you are searching for patents granted prior to 1976 and these patent are not text-searchable on the USPTO web site. The PTDL Program provides a large amount of official documents in paper and electronic formats to libraries joining the PTDL Program, beginning with the year of PTDL designation. Part of the official material supplied to a PTDL are the Annual Indexes of Patents, Parts I and II, and the Official Gazette — Patents. The Annual Index of Patents, Part I is the List of Patentees, and this is probably the most valuable when searching old patents, as the patentee (or inventor) and the assignee (the person or company who owns part of or all of the patent) are listed alphabetically. All patents granted to an inventor are listed, and this will enable the researcher to quickly find the patents of interest. Currently, the most recent issue of the Annual Index of Patents is for the year 1997. If you are lucky, and the library closest to you has been part of the PTDL program for a long time, say back to 1900, then it is likely that they will have copies of the Annual Indexes back to 1900. If not, you may have to check with another PTDL library.

Once you have checked the Annual Indexes, and obtained the patent numbers you are seeking, it is then just checking the patents on the USPTO Web Site for viewing or printing.

There are also two books that are valuable when searching for specific patents dealing with automatic guns, and these are Volumes 4 and 5 of Chinn’s The Machine Gun series. The original 4-volume set of books covered US Patents relating to automatic guns up to 1954 while the fifth volume covered US Patents from 1955 through to 1971. If your field of interest is in automatic guns, these books are invaluable, as they give the patent number and patentee name(s), along with a brief abstract of the patent. Once you have the patent number, it’s a simple step to the Internet to view, save or print out the relevant patent.

To understand the world of patents, you need to understand about the classification system, which is the heart of the USPTO. Understanding the classification system and the various search fields will allow you to search an extremely valuable asset, an asset that directly chronicles the technological development of man.

In the firearms world, patents are a valuable asset for many companies and individual inventors/designers, as they represent formal recognition and protection of the unique designs that have been developed by the companies or the inventors/designers. So enjoy your searching. I’m sure you’ll find it an extremely interesting experience.

The HEL M2 was an experimental M16 suppressor that used a series of baffles coupled with an expansion chamber extending back over the barrel to the front sight. The M2 model for the M16 rifle was 14 inches long and used 24 baffles forward of the muzzle. Following an ENSURE (Expediting Non-Standard Urgent Requirement for Equipment) request (DA ENSURE Index No. 77) from the USARV (United States Army, Vietnam) for silencers for the M16A1 rifle in May 1966, HEL designed and tested a noise suppressor designated the HEL M4, which was a variant of the M2.

To reduce the bulk and weight of the M2 5.56mm suppressor, HEL shortened the length to 12 inches, reduced the number of baffles, and changed the internal arrangement of components. The number of baffles was reduced from 24 to 11, with the first baffle being positioned backwards (i.e., so that its apex was toward the front of the suppressor). Directly in front of this baffle was a short expansion chamber followed by a baffle positioned normally (i.e., with its apex toward the muzzle of the rifle). This baffle had a very large bullet passage, presumably to reduce back pressure. The next 9 baffles were the same design as the first baffle, but were oriented normally.

The new can eliminated enough of the muzzle blast so that the location of the shooter was undetectable to hostiles downrange, which greatly improved a shooter’s tactical advantage and survivability. Given ideal vegetation and terrain, the muzzle blast from an M16A1 was completely indistinguishable beyond 50 yards. Only the sonic boom created by the 5.56mm projectile remained, which sounds something like the report of a short-barreled .22 rifle. In the absence of a muzzle blast, the mammalian brain interprets the origin of the gunshot as perpendicular to the pressure wave of the ballistic crack striking the body. Combined with the sound of bullet impact, this phenomenon causes individuals to turn their attention 90 to 180 degrees away from the shooter. This is a very good thing during an ambush or when a small force equipped with silencers must cope with a larger force.

To meet the ENSURE #77 requirement, the USARV submitted an acquisition requirement for 1,080 HEL M4 noise suppressors. By December 1967, the first 120 suppressors had been produced, but further production was suspended pending a field evaluation by USARV. Twenty suppressors were sent to USARV for testing.

In March and April 1968, the USAIB (United States Army Infantry Board) tested the M4. The USAIB test found that the M4 had three shortcomings. (1) The gas deflector failed to deflect all of the escaping gases from the firer’s eyes. (2) The ejection pattern of the rifle with noise suppressor attached caused the spent cartridge case to strike the cheek of left-handed shooters. And (3) the malfunction rate of the test rifle was significantly higher than the control rifle during automatic fire. The USAB concluded that the HEL M4 sound suppressor had military potential but it was not the perfect tool for the job, so the Board returned the M4 to HEL for correction of these shortcomings.

Early development at Aberdeen also demonstrated that the M4 generated a number of problems with the M16A1 rifle: (1) increased back pressure; (2) increased cyclic rate; (3) increased rearward bolt velocity, and (4) excessive gas discharge from the ejection port into the shooter’s face. The major problem was the increased back pressure, which actually produced the other problems, such as shearing off the bolt carrier key. HEL solved the bolt velocity and cyclic rate problems by adding an additional gas pressure relief port to the bolt carrier, which enabled reliable functioning of the rifle whether the selector was set to SEMI or AUTO.

The only glitch with this solution was that the rifle would not cycle reliably with the modified bolt carrier unless the suppressor was installed. This meant that a rifle fitted with the modified bolt carrier had to be dedicated for suppressed use only.

Once installed, the suppressor became an integral part of the rifle that could not be removed without swapping the bolt carrier as well. This was not an ideal situation for special operators. Furthermore, the suppressed rifle with modified bolt carrier still dumped a lot of hot combustion gas into the shooter’s face, so HEL added a special gas deflector to the charging handle of the M16A1 rifle. This deflector was not entirely successful, however. In April and May 1968, HEL developed a new, shorter suppressor that eliminated the need for a specially modified bolt carrier. Apart from the removal of 5 baffles from the baffle stack, the new suppressor used the same arrangement forward of the muzzle of the rifle. This new 9.5 inch model was known variously as the HEL M4A, or H4A, or E4A which was its final designation. The gas deflector was also intended to be used with the new suppressor, but there is little evidence to suggest that it was actually used with the E4A suppressors in the field.

Other developers of noise suppressors tried to meet the ENSURE #77 requirement, including SIONICS (a commercial company that eventually merged with the Military Armament Corporation) and Frankford Arsenal (FA; which was a government facility). In May 1968, HEL, SIONICS and FA submitted a total of seven different noise suppressors for testing to meet the ENSURE #77 requirement. The Frankford Arsenal silencers were 1.25 inches in diameter and utilized porous aluminum rather than baffle technology. These very early SIONICS silencers used WerBell’s spiral diffusers, but did not incorporate baffles that would later be seen in his patents and production units. They also featured a flash hider that screwed onto the front end cap of the SIONICS silencer. The HEL M4 and M4A suppressors were tested at Ft. Benning, Georgia, by the USAIB in a Military Potential Test (MPT) against the FA (Frankford Arsenal) FA XM and CM noise suppressors and three different versions of the SIONICS 5.56mm suppressor (the MAW-A1, A2, and A3 models). The test recommendation was that the HEL E4A noise suppressor was suitable for a field evaluation in Vietnam.

The HEL E4A was win-win technology. While it was not as quiet as the M4, it solved all of the reliability and durability issues plaguing the M4 suppressor. Furthermore, it was more compact than the HEL M4. While the E4A did not require a modified bolt carrier (unlike its M4 predecessor), we find it quite interesting that the E4A was considered to be a permanent fixture once it was fitted to a rifle.

The E4A produced a net sound reduction of 26 dB (at 12.5 feet down range and 2 feet to the right of bullet trajectory). That was significantly better than the SIONICS suppressors (by about 10-11 dB), but not as good as the HEL M4 (which produced 35-36 dB reduction) or the FA XM (which produced 32-36 dB reduction). See the accompanying sidebar to learn more about the sound level measurement procedures used for these HEL tests. All of the other five suppressors tested by the USAIB had shortcomings. The performance of the E4A out-shone the other suppressors, especially with regard to the number of malfunctions that occurred during cyclic tests. The malfunction rate of the E4A was significantly lower than all other suppressors tested; during a 1,000-round cyclic rate test, only 3 malfunctions occurred with the E4A.

While some shortcomings were noted with the SIONICS suppressors, SIONICS was well advanced in the use of high-tech materials compared to the other suppressor manufacturers of the time. SIONICS used a plastic bushing under the rear retaining collar. Unfortunately, this bushing melted during a full-auto testing. A redesigned bushing made from Teflon was then submitted during the MPT to rectify this problem. Unfortunately, Teflon melted when temperatures reached about 1,000 degrees F, so SIONICS finally settled upon making the bushings from naval bronze.

Another problem was the gas pressure relief valve. The springs used in the relief valve failed during the cyclic rate testing, so a redesigned spring made from Inconel was submitted in an attempt to rectify this problem. Even resorting to using a high-temperature resistant alloy like Inconel proved unsuccessful, so SIONICS developed its third and final design: a passive gas pressure relief valve with no moving parts. Significantly, the MPT found that the pressure relief valve had no effect on the operation of the test items, and concluded that it was an unnecessary part of the suppressor. It is also interesting to note that use of a gas pressure relief valve with center-fire rifle suppressors has not been seen since its use in the SIONICS suppressors, with one exception. Recently deployed Israeli-made centerfire rifle suppressors for the M16A1 and M14 rifles have featured the use of gas pressure relief valves, despite the fact that advances in internal design have clearly eliminated any need for pressure relief valves.

Two of the SIONICS suppressors used titanium spiral suppressor rings, while the third used aluminum spiral suppressor rings. Following further destruct tests at Ft. Benning, SIONICS made significant changes to the construction and materials used in the 5.56mm suppressors. No internal parts were subsequently made from aluminum, and stainless steel became the material of choice. While the use of titanium has become more widespread in recent years, it is a little-known fact that SIONICS pioneered the usage of titanium in firearms sound suppressors, though undoubtedly the cost factor prevented its widespread use during the Vietnam years. Despite the advances in material use, the SIONICS/MilitaryArmament Corporation’s suppressors were not as widely used as the HEL E4A in Vietnam.

After the MPT report was published in September 1968, final production of the outstanding 960 HEL E4A suppressors was completed, and these were shipped to Vietnam in late 1968 and early 1969 at a cost of $42,000. That works out to less than $46 per unit. According to several sources, the HEL E4A suppressor was used in greater numbers during the Vietnam War than SIONICS/Military Armament Corporation’s suppressors designed for the M16A1 and CAR-15. Rangers, SEALs and Army Special Forces began using HEL M4 silencers in the summer of 1968 and then upgraded to the HEL E4A suppressors, which were employed throughout the remainder of the Vietnam War. The SEALs, however, eventually used a U.S. Navy-developed 5.56mm suppressor rather than the E4A suppressor.

Surprisingly, both the HEL M4 and E4A suppressors were considered to be expendable items. If they were damaged, they were to be destroyed by the company armorer rather than repaired. This may explain why the HEL M4 and E4A suppressors are rarely seen today in collectors’ hands. It is known that during the early 1980s, at least one mail-order company was selling parts kits for the M4, although this practice ceased when ATF changed the definition of a silencer to include silencer parts. If you ever find a transferable M4 silencer, it’s a rare and important historical artifact from the Vietnam War.