MAGNESIUM FIREARM FOREARM AND METHOD OF MANUFACTURE

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to firearms, parts thereof, and methods of manufacturing such parts.

2. Description of the Related Art

Firearms generally include three main parts, the barrel through which a projectile, e.g., a bullet, is fired; the action which includes the moving parts that provide for the loading, firing, ejection of fired casing, and unloading; and either a stock (shotguns and rifles) or grip (handguns). The receiver houses most, if not all, of the operating parts that form the action of the firearm. The receiver is often made out of steel or aluminum. Under U.S. law, the receiver is generally the legally controlled part that is considered to constitute the firearm itself and which has a serial number fixed thereon.

Long arms, such as rifles and shotguns, will often have a forearm which extends forward of the receiver and at least partially surrounds the barrel. Typically, the forearm provides a location for the user to grip the firearm with their off-hand. While some forearms are positioned adjacent only the lower portion of the barrel and do not completely encircle the barrel, it is also known to use a forearm that completely encircles the barrel and also serves as a barrel shroud. A barrel shroud protects the user by inhibiting contact between the user and a barrel that has become heated due to firing of the gun.

The barrel of the gun may either be in contact with the forearm or be positioned proximate but slightly spaced from the barrel. When the barrel is not in direct contact with the forearm, it is generally referred to as a free floating barrel. Such free floating barrels are typically secured to the receiver and this attachment point serves as their sole point of attachment and support. Free floating barrels are generally considered to be more accurate than barrels which bear against the forearm because it is thought that the pressure exerted on the barrel by the contact between the barrel and forearm can change slightly from shot-to-shot thereby causing inconsistent bullet flight paths. A free floating barrel is not subject to such potentially variable contact pressure. The barrel of a firearm is generally attached to the receiver for both free-floating barrels and barrels which contact the forearm of the gun.

While many firearms have a unitary receiver, some have multiple receivers. For example, one common form of firearm, often referred to as an AR-style rifle, has both an upper and lower receiver which are detachably secured together. This type of rifle gets its name from the AR-15 originally introduced by Armalite and which was adopted by the U.S. military as the M-16 rifle. The M-16 is a selective fire weapon capable of both semi-automatic and fully automatic operation. A civilian version of the M-16 capable only of semi-automatic fire was subsequently developed by Colt's Manufacturing Company and sold as the Colt AR-15. For AR-style rifles, the lower receiver generally constitutes the serialized component that is legally controlled as a firearm.

AR-style rifles are modular rifles which include an upper receiver assembly having an upper receiver, a bolt carrier, a barrel and a forearm. The forearm of AR-style rifles often takes the form of a barrel shroud and, as a result, is commonly referred to as a handguard. The lower receiver assembly includes a lower receiver which houses a trigger assembly and has a port for receiving a magazine. A pistol grip and stock can be attached to the lower receiver.

The modular nature of the rifle provides several benefits. For example, it allows the rifle to be easily customized for a particular application. The modular nature of the rifle also allows an individual component or one of the sub-assemblies to be easily replaced if the original is damaged or an alternative design is preferred. The many advantages provided by AR-style rifles, also known as modern sporting rifles, have resulted in such rifles becoming one of the most popular styles of firearm produced today.

While conventional firearm designs and manufacturing techniques are capable of producing satisfactory firearms, improved cost-efficiency in the manufacture of firearms and design modifications which improve the manufacturability remain desirable.

SUMMARY OF THE INVENTION

The present invention provides a firearm forearm that includes a magnesium alloy body and a method of manufacture. The disclosed forearms are light weight and allow for the cost-efficient manufacture of the forearms.

The invention comprises, in one embodiment thereof, a firearm that includes a receiver operably coupled with a barrel and a forearm securable to the firearm wherein the forearm includes a magnesium alloy body.

The magnesium alloy body may advantageously be nickel plated. An oven-cure ceramic coating can be applied to the nickel plating. In some embodiments, the firearm is a modular rifle wherein the receiver includes an upper receiver and a lower receiver; the forearm and the barrel being mountable on the upper receiver and the lower receiver housing a trigger assembly. The barrel may be a free floating barrel that is spaced from the forearm.

In some embodiments, the magnesium alloy body forms an outer sleeve and the forearm further comprises an inner sleeve formed out of a non-magnesium material, the outer sleeve being disposed about and engaged with the inner sleeve. The inner sleeve may include a steel material.

The forearm may be defined by a pair of separable parts which substantially encircle the barrel when secured together. Alternatively, the forearm may be a unitary forearm which substantially encircles the barrel.

The invention comprises, in another form thereof, a method of manufacturing a firearm forearm that includes forming a magnesium alloy body and processing the magnesium alloy body to form at least a portion of the forearm.

In some embodiments, the magnesium alloy body has a layer of nickel plating formed thereon by a nickel plating process and a ceramic coating is then applied on the layer of nickel plating.

The magnesium alloy body may be formed by thixotropically molding the body. When thixotropically molding the body, the magnesium alloy body advantageously has a surface roughness, R_a, that is between approximately 35 microinches and approximately 60 microinches after molding and without any post-molding processing to smooth the surface. Alternatively, the step of forming a magnesium alloy body may include extruding the magnesium alloy body.

In some embodiments, the extruded magnesium alloy body forms a forearm that substantially encircles the barrel. After extruding the magnesium alloy body, the body may be cut lengthwise to form two separable parts of the forearm. The two separable parts advantageously have the same configuration.

In some embodiments, the forearm includes an inner sleeve and an outer sleeve disposed about the inner sleeve wherein the magnesium alloy body forms the outer sleeve of the forearm and a non-magnesium insert is provided to form the inner sleeve. Advantageously, the magnesium alloy body forming the outer sleeve is formed by extrusion.

The magnesium alloy body may be formed out of an AZ91D magnesium alloy. In some embodiments, the forearm has a configuration which adapts the forearm for use in a modular rifle having both a lower receiver housing a trigger assembly and an upper receiver securable to a barrel.

BRIEF DESCRIPTION OF THE DRAWINGS

The above mentioned and other features of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side view of a firearm having a magnesium forearm.

FIG. 2 is another side view of a firearm.

FIG. 3 is view of a firearm broken down into several major sub-assemblies.

FIG. 4 is an exploded view of a lower receiver and extension assembly, buttstock and grip.

FIG. 5 is a perspective view showing the removal of a two piece forearm from a rifle.

FIG. 6 is an exploded view of an upper receiver, barrel and two piece forearm.

FIG. 7 is a perspective view of a one piece forearm.

FIG. 8 is an exploded perspective view of a forearm with a reinforcing insert.

FIG. 9 is an end view of a forearm with a reinforcing insert.

FIG. 10 is an exploded end view of a two piece forearm.

FIG. 11 is an exploded perspective detail view of a two piece forearm.

FIG. 12 is a schematic depiction illustrating the molding of a forearm.

FIG. 13 is a schematic depiction illustrating the extruding of a forearm.

FIG. 14 is a perspective view of an extrusion.

FIG. 15 is a cross sectional view of an extrusion die taken along line A-A of FIG. 16.

FIG. 16 is an end view of an extrusion die.

FIG. 17 is a schematic depiction of a machining center for the machining of a forearm.

FIG. 18 is a schematic cross section of a portion of a forearm.

Corresponding reference characters indicate corresponding parts throughout the several views. Although the exemplification set out herein illustrates an embodiment of the invention, in one form, the embodiment disclosed below is not intended to be exhaustive or to be construed as limiting the scope of the invention to the precise form disclosed.

DETAILED DESCRIPTION OF THE INVENTION

A firearm 30 having a lower receiver in accordance with the present invention is shown in FIGS. 1 and 2. Firearm 30 is an AR-style rifle and, except for the forearm assembly 70, has a conventional design and construction which is well-known to those having ordinary skill in the art.

FIG. 3 illustrates firearm 30 with several of the major sub-assemblies being disconnected. More specifically, firearm 30 has been broken down to separate the lower receiver and extension assembly 32, the upper receiver and barrel assembly 34, the bolt and carrier group 36, and the charging handle 38. These sub-assemblies, e.g., lower receiver and extension assembly 32 and upper receiver and barrel assembly 34, can be further broken down into still smaller modular assemblies.

FIG. 4 provides an exploded view of the lower receiver and extension assembly 32. Illustrated in FIG. 4 are helical compression spring 1, buffer assembly 2, hammer assembly 3, sear 4, selector lever 5, helical compression spring 6, bolt catch plunger 7, bolt catch 8, spring steel pin 9, magazine catch 10, helical compression spring 11, pin 12, helical compression spring 13, magazine catch button 14, pivot pin 15, disconnector 16, trigger assembly 17, screw 18, lock washer 19, grip 20, helical compression spring 21, safety detent 22, grooved pins 23, grooved pin 24, takedown pin 25, stepped spacer 26, buttstock assembly 27, self-locking screw 28, receiver extension tube 29 and lower receiver 40. The assembly and operation of the parts shown in FIG. 4 will be understood by those having ordinary skill in the art.

The upper receiver and barrel assembly 34, which includes a forearm, is shown in greater detail in FIGS. 5 and 6. The illustrated forearms are adapted for use with AR style rifles and also function as a heat shield and as a handguard, however, alternative embodiments can be employed with other firearms. The terms handguard and forearm are used interchangeably herein.

The forearm assembly shown in FIGS. 5 and 6 is a two-piece assembly 70a having a pair of separable parts 72a that encircle the barrel. FIG. 5 illustrates the removal from rifle 30 of one of the two handguards 72a that form forearm 70a. FIG. 6 is a view of upper receiver and barrel assembly 34 with the handguard assembly 70a detached from assembly 34. Assembly 34 includes the upper receiver 33 which is secured to barrel 35. A slip ring assembly 64 is mounted proximate the attachment of barrel 35 to upper receiver 33 and a front sight assembly 66 is mounted on barrel 35 near muzzle 68.

Handguards 72a are removed from rifle 30 by pressing slip ring 64 toward upper receiver 33 and away from front sight 66. Slip ring 64 is biased toward muzzle 68 and front sight 66 by a spring (not shown). Slip ring 64 surrounds a reduced diameter collar 74 on handguards 72a. After depressing slip ring 64, one of the handguards 72a can be removed by pivoting the released end of the handguard 72a away from barrel 35 and disengaging handguard 72a from handguard cap 76. Handguards 72a may have retaining tabs (not shown) which fit within openings or recesses in cap 76 or otherwise engage cap 76 to thereby secure the muzzle end of handguard assembly 70a. FIG. 5 illustrates one person pressing down on slip ring 64 and a second person removing a handguard 72a, however, it is will generally be possible for a single individual to remove handguard assembly 70a without assistance. To attach the handguards 72a, the process is reversed.

Alternative method of attaching the forearm may also be employed. For example, the forearm could be provided with helical threads for securely engaging the firearm or a groove which receives a retractable projection. In still other embodiments, the forearm could be provided with apertures through which fasteners are extended to secure the forearm to the firearm. Other suitable methods of securing the forearm to the firearm may also be employed.

As can be understood with reference to FIGS. 5 and 6, handguard assembly 70a substantially encircles barrel 35 with each of the two similarly configured handguards 72a engaging each other along surfaces 80 that extend along the length of barrel 35. Vent openings 78 in handguards 72a allow air to escape and thereby dissipate heat from the space between barrel 35 and handguard assembly 70a.

It is noted that the handguard assembly 70a depicted in FIGS. 5 and 6 has a slightly tapered configuration wherein the diameter of the handguard assembly 70a is largest near upper receiver 33 (excluding collar 74) and becomes progressively smaller toward cap 76. In this regard, it is also noted that the handguard assembly 70 shown in FIGS. 1 and 2 also has a tapered shape. The handguard assembly of FIGS. 1 and 2 differs from the assembly of FIGS. 5 and 6 by having an exterior surface with a plurality of recesses while the assembly of FIGS. 5 and 6 has a generally smooth exterior surface. The recesses on the assembly of FIGS. 1 and 2 enhance the ability of the user to securely grip the forearm.

The handguard assemblies illustrated in FIGS. 3, 7, 8, 9, 10 and 11 are not tapered and have a more cylindrical configuration. It is further noted that while the handguard assembly of FIGS. 5 and 6 are two piece handguards, the handguard assemblies of FIGS. 7, 8 and 9 are unitary handguards. The unitary handguard assemblies have a tubular form and must be slid into place either before barrel 62 is attached to upper receiver 60 or before the front sight assembly 66 is mounted on barrel 62 (if a front sight assembly is being used). The mounting of the handguard assembly on the rifle, whether a two piece or unitary design, will depend on the particular details of the rifle design as will be well-understood by a person having ordinary skill in the art.

Handguard assembly 70b shown in FIG. 7 is a unitary handguard and has a plurality of vent openings 86 formed therein. Handguard 70b also includes an interior threaded portion (not shown) for securing handguard 70b to upper receiver 60. Lugs 88 may be used to secure a bipod or other device to handguard 70b. The interior threads are located at the same end as lugs 88. Handguard 70b also includes four sections of a mounting rail such as a Picatinny rail. In the embodiment of FIG. 7, the top and bottom sections 82a, 82b extend for substantially the entire length of handguard 70b while the side sections 82c extend only a portion of the length.

Mounting rails 82a-82c provide a standardized mounting feature for attaching accessories, such as a scope or light source, to the forearm. Picatinny rails are one of the more common types of mounting rail and are also known as MIL-STD-1913 rails and have generally T-shaped cross section with a series of spaced slots 84. Those having ordinary skill in the art will recognize that the shape of such rails has been standardized to allow for the attachment of a wide variety of different accessories and that the use of such rails on the forearm of an AR style rifle and other firearms is a common and known practice.

FIGS. 8 and 9 illustrate a variant of FIG. 7. The embodiment illustrated in FIG. 7 is a unitary handguard that is made entirely out of magnesium. The handguard assembly 70c illustrated in FIGS. 8 and 9 has a magnesium outer sleeve 85 and an inner reinforcing sleeve 83 which is formed out of a stronger material. For example, inner sleeve 83 may be a steel or aluminum tube. In this regard, it is noted that some magnesium alloys have a greater strength than others. The embodiment illustrated in FIG. 7, for example, can be manufactured using an AZ91B magnesium alloy without the use of a reinforcing tube. Other magnesium alloys, AZ91D, for example, do not have physical properties which are identical to AZ91B and may require a reinforcing sleeve 83. The need for a reinforcing sleeve is dependent not only on the material used to form the outer sleeve but also on the dimensions and configuration of the forearm. Not all forearms using an AZ91D alloy will necessarily require the use of reinforcing sleeve nor will all forearms using an AZ91B alloy necessarily be sufficiently strong without an insert. Moreover, it may be desirable to provide additional strength to the forearm through the use of a reinforcing sleeve 83 even if the material used to form the outer sleeve would be strong enough without such a sleeve.

When using a reinforcing sleeve 83, the outer radial surface 83a of reinforcing sleeve 83 contacts the inner radial surface 85a of outer sleeve 85 over a substantial portion of the surfaces 83a, 85a which face each other. The illustrated embodiment includes an inner sleeve 83 with vent openings 86a which align with the vent openings 86 of outer sleeve 85. The illustrated inner sleeve 83 and outer sleeve 85 also have the same length. Alternative embodiments, however, may employ different arrangements of the inner and outer sleeve. For example, the outer sleeve could include vent openings that expose a portion of the inner sleeve or the two sleeves could have differing lengths. It may also be desirable in some embodiments for the inner sleeve to have more openings than the outer sleeve to reduce the weight of the inner sleeve while still providing the desired reinforcing strength or the inner sleeve might not include any vent openings. Although the two sleeves could be slidingly engaged and not fixed together, it will generally be desirable to permanently secure the two sleeves 83, 85 together. The two sleeves 83, 85 can be secured together using welds, a press-fit engagement, or other appropriate method.

FIGS. 10 and 11 illustrate another variant of the forearm of FIG. 7. The embodiment of FIGS. 9 and 10 is formed by taking the forearm of FIG. 7 and cutting it in half to form a two piece handguard assembly 70d having a pair of separable parts 72d that encircle the barrel when secured together. Each of the two resulting handguards 72d have engagement surfaces 90 which abut with surfaces 90 of the opposing handguard 72d when the two handguards 72d are secured about a barrel 35. The two handguards 72d can be secured together using various methods known in the art such that described above with regard to the embodiment of FIGS. 5 and 6. The embodiment of FIGS. 9 and 10, however, use threaded fasteners. As seen in FIG. 10, an access area 96 and an aperture 98 are cut in the handguards 72d and threaded fasteners 92 are engaged with nuts 94 to secure the two handguards 72d together to form handguard assembly 70d, for example, four sets of fasteners 92 and nuts 94 can be used to secure the handguards 72d. It is also noted that instead of using a loose nut 94, threaded inserts could be embedded in one of the handguards 72d to engage threaded fasteners 92.

A variety of other modifications can also be made to the illustrated handguard assemblies. For example, AR style rifles originally all used a gas impingement system to cycle the spent shell casing and load a new round into the chamber. In a gas impingement system, propellant gases are bled from a port in the barrel into a tube which conveys the pressurized gas to a location where it can impinge upon the bolt carrier and perform the cycling operation. In recent years, a number of manufacturers have begun manufacturing AR style rifles with a gas piston system. In this alternative, pressurized gases are bled from the barrel through a port and impinge upon a piston. A rod connected to the piston is used to impinge upon the bolt carrier. In gas piston systems, the hot and dirty propellant gases are not introduced into the receiver to thereby reduce fouling of the action of the firearm. Because the tube conveying the gases or the piston and rod assembly acted upon by the propellant gases is typically located alongside barrel 35 for AR style firearms, the configuration of the handguard assembly will often be influenced by whether the firearm is using a gas impingement or gas piston system. Various configurations of handguards suitable for use with gas impingement systems and gas piston systems are well known to those having ordinary skill in the art and can be employed with alternative embodiments of the present invention.

The illustrated handguards can be formed by injection molding a thixotropic, semisolid magnesium alloy and subsequently applying a nickel coating using an electroless nickel plating process. In this regard, it is noted that handguards for AR-style rifles are most commonly formed out of aluminum or plastic. Magnesium is lighter than aluminum and comparable in strength. For example, lightweight magnesium alloys may be 35% lighter than aluminum alloys. Although plastic is lighter than magnesium, magnesium is significantly stronger.

As mentioned above, magnesium alloys such as AZ91B and AZ91D can be used when molding the illustrated handguards. The composition of an AZ91B magnesium ally may include by weight 8.3 to 9.7% Al, 0.13% Mn min., 0.35 to 1.0% Zn, 0.50% Si max., 0.35% Cu max, 0.03% Ni max, and 0.30% max other (total) with Mg forming the balance of the alloy. The composition of an AZ91D magnesium alloy may include by weight 8.5-9.5% Al, 0.45-0.90% Zn, 0.17-0.4% Mn, ≦0.05% Si, ≦0.025% Cu, ≦0.001% Ni, and ≦0.004% Fe with Mg forming the balance of the alloy. Magnesium alloys such as AZ91B and AZ91D are commercially available and well-known to those having ordinary skill in the art.

The use of a thixotropic injection molding process to form handguard assemblies 70a-70d is schematically depicted in FIG. 12. Molding machine 100 includes a supply system 102 for feeding magnesium chips and an inert gas supply 104. The introduction of an inert gas such as argon prevents the magnesium from igniting. The magnesium chips and inert gas are fed into an injector barrel housing a screw 106. Heating elements 108 heat the content of the barrel. Heating elements 108 partially melt the magnesium chips while screw 106 provides the shearing force necessary to create a thixotropic slurry out of the semi-molten magnesium. Injector mechanism and accumulator 110 accumulate and then force the thixotropic magnesium into mold 112 under high pressure. After allowing the magnesium to cool within mold 112, the mold is opened to remove the forearm.

Thixotropic injection molding typically provides a laminar melt flow at a relatively low temperature which provides for quick cooling with limited shrinkage and high dimensional accuracy. Thixotropic injection molding also typically results in relatively high densities and low porosity. The dimensional stability and tight tolerances obtainable by thixotropic injection molding is result of several factors including laminar flow of the thixotropic slurry into the mold, the high pressures used when filling the mold and rapid solidification. The high dimensional stability, tight tolerances and low draft obtainable by thixotropic injection molding of a magnesium alloy allows for the molding of complex geometries.

The molded handguards also have a semi-smooth surface. After molding, and without any post-molding processing, it is possible to obtain a surface having a surface roughness, R_a, of approximately 35 microinches to approximately 60 microinches (approximately 0.00089 mm to approximately 0.0015 mm) when thixotropically molding a magnesium alloy. The semi-smooth skin and ability to mold complex geometries held to tight tolerances, allow handguards to be molded with preformed openings and other design features that might otherwise require significant machining to form. Furthermore, for those features that are machined, magnesium is a relatively easy material to machine.

Minimizing the machining of the handguards is advantageous not only for reasons of manufacturing efficiency but also because it reduces the small particles of magnesium that are generated during the machining process. Small particles of magnesium are relatively easily ignited and thus must be carefully handled. Minimizing the volume of such particles is advantageous.

In the illustrated embodiments, it is noted that the general structure of Picatinny rails 82a-82c can be formed by the molding operation with Picatinny rail slots 84 and other engagement surfaces of the Picatinny rails 82a-82c being machined after the molding operation. It may also be advantageous to roughly mold slots 84 in rails 82a-82c and clean up the surfaces with post-molding machining operations. While it may also be possible to form rails 82a-82c by the molding operation alone and without any post-mold machining, it will generally be desirable to machine the engagement surfaces of rails 82a-82c to obtain tightly controlled tolerances. Vent openings in the handguards are advantageously formed by molding but could alternatively be subject to limited post-molding machining or formed entirely by post-molding machining operations.

FIG. 17 schematically depicts a CNC machining center 184 that can be used to machine the magnesium alloy bodies forming the handguards to achieve the desired final shape. The illustrated CNC machining center 184 includes a workbed 186. A carriage 188 allows tooling 190 to be repositioned relative to workbed 186. A controller 192 controls the operation of the tooling 190. Various other machining equipment known in the art can also be used when machining the handguard assemblies.

After molding and machining the handguard, it is tumbled in a ceramic media for deburring, then cleaned and plated. Either an electroplating or electroless plating process can be used to plate the handguard. Plating the magnesium body protects the magnesium from corrosion, notably galvanic corrosion.

Although electroplating can be employed, an electroless nickel plating process provides several advantages. Electroless nickel plating is an auto-catalytic chemical process that deposits a nickel-phosphorus layer on the magnesium components of the handguards. In an electroless nickel plating process, a reducing agent is used to react with metal ions to deposit metal on the object being plated. In the illustrated example, a layer of nickel is deposited on the handguards. Unlike electroplating, electroless nickel plating does not require the use of an electrical current to form a deposit on the work piece. The absence of flux-density and power supply variations allows the electroless nickel plating process to provide a more even deposit on complex geometry than would an electroplating process. The use of an electroless nickel plating process also provides the handguard with a more durable coating than would a conventional ion-exchange chromating process.

Once plated, the handguard can be assembled in a firearm 30. If the handguard will be combined with an inner sleeve, the inner sleeve and outer magnesium sleeve will be combined before installing on the firearm 30. The electroless nickel plating also allows for the application of one or more additional layers of material such as those applied to firearm components made out of traditional materials. For example, another layer of plated material using traditional plating methods could be applied to the electroless nickel plating layer. Alternatively, it may be desired to apply a camouflage pattern to the handguard. Materials and methods of applying camouflage patterns to firearms is well-known in the art.

An oven-cure ceramic coating can be applied to the nickel plating to provide it with the desired color and/or camouflage pattern as well as enhance the wear and weather resistance of the forearm. For example, a Cerakote™ coating commercially available from NIC Industries, Inc. located in White City, Oreg. can be applied over the electroless nickel plating layer and form the exterior layer of the handguards. The application of various other material layers to enhance the appearance, wear or weather resistance of a firearm that can be applied to a nickel plated surface using traditional methods are also well known to those having ordinary skill in the art.

FIG. 18 schematically depicts a cross section of a portion of a forearm and the thickness of layers 122 and 124 is exaggerated for purposes of graphical clarity. As can be seen in FIG. 18, a magnesium alloy body 120 forms the structure of the illustrated portion of the forearm and has a layer of plating 122 deposited thereon. In the illustrated embodiment plating layer 122 is a layer of nickel plating. Deposited on top of plating 122 is a layer of ceramic coating 124. In the illustrated embodiment, both the plating layer 122 and ceramic coating 124 are applied to all surfaces of the magnesium alloy body 120. It will generally be desirable to apply a plating layer 122 to all surfaces of the magnesium body 120. Ceramic coating 124 can also be advantageously applied to all external surfaces of the magnesium body as exemplified in the illustrated embodiment. In some embodiments, however, it may be desirable to be more selective as to which surfaces receive plating 122 and ceramic coating 124. For example, it may be desirable to omit either plating 122 or coating 124 from the inner surface of a magnesium alloy body forming the outer sleeve of a forearm that receives an inner sleeve.

Turning now to FIGS. 13-16, another method of manufacturing a handguard/forearm will be discussed. The method illustrated by FIGS. 13-16 involves the extrusion of the forearm. FIG. 13 schematically depicts an extruder 170 that can be used to form an extrusion having the shape of unfinished forearm 162 in FIG. 14. Extruder 170 includes a hydraulic press 171 which powers a ram 172. Ram 172 extends into container 174 which holds a billet 176 of the material to be extruded. A dummy block, not shown, is placed between billet 176 and ram 172. A die 180 is installed at the end of container 174 opposite ram 172. Controls 178 govern the operation of extruder 170. As ram 712 is extended, billet 176 is forced through die 180 to form an extrusion with the configuration of unfinished forearm 162.

When using an extruder, the billet may either be cold or heated. In a cold extrusion process, the billet is placed in the container in a solid form at ambient temperature. Alternatively, the billet may be heated before it is placed in the container. In a hot extrusion process, the billet is heated to a temperature above the recrystallization temperature of the material. In a warm extrusion process, the billet is heated to a temperature above the ambient temperature but below the recrystallization temperature of the material.

Although magnesium alloys can be cold extruded, when forming an extruded forearm a warm or hot extrusion process is advantageously employed. For example, the billet may be an AZ91D magnesium alloy. The composition of AZ91D magnesium alloys is known in the art and typically includes about 8.5-9.5% Al, 0.45-0.90% Zn, 0.17-0.4% Mn, ≦0.05% Si, ≦0.025% Cu, ≦0.001% Ni, and ≦0.004% Fe with Mg forming the balance of the alloy. This alloy has high strength and good corrosion resistance and is often used for the housings of electric appliances.

FIG. 14 illustrates an unfinished forearm 162 that can produced by extruder 170. As can be seen in this figure, unfinished forearm 162 defines an axially extending centerline 164. Unfinished forearm 162 has a cylindrical section 165 that extends parallel with and concentrically about centerline 164. T-shaped projections 166 extend outwardly from cylindrical portion 165 and will define a mounting rail such as a Picatinny rail in the finished forearm. Cylindrical section 165 also defines an axially extending center bore through which barrel 35 will extend when the forearm is mounted on a firearm 30.

When forming an extrusion with extruder 170, the extrusion may have an axial length parallel with centerline 164 that is equivalent to or slightly longer than a single forearm by selecting an appropriately sized billet 176. Advantageously, a larger billet 176 is used and the extrusion has an axial length that is longer than a single forearm and equivalent to or slightly longer than a whole number of individual forearms whereby the extrusion can be cut transverse to centerline 164 to thereby form a plurality of forearms from a single extrusion. Each of the individual unfinished forearms 162 can then be machined to form a finished forearm. The use of a billet having a size sufficient to form several forearms from a single extrusion will generally provide manufacturing efficiencies over the use of a billet sufficient only for a single forearm.

As depicted in FIG. 14, unfinished forearm 162 has a bore 168 formed therein during the extrusion process. FIGS. 15 and 16 schematically depict a die 180 which can be used to form an extrusion having a bore extending therethrough. As is known in the art, a mandrel can be used to form a centrally located opening in an extrusion. The illustrated die 180, includes a mandrel 194 having support legs 196 and a leading edge 198. The billet first contacts leading edge 198 and is pierced thereby. The support legs 196 support center die 200 which forms center bore 168. Support legs 196 are located only proximate the leading edge of die 180 and allow the material to reform within die 180 after passing by legs 196. Depending upon the precise parameters of the extrusion process, the finished extrusion may include weld lines at the location of legs 196 as a result of the extrusion process. Once the extrusion is formed and has cooled, it is cut to length to form a plurality of unfinished forearms 162.

After forming unfinished forearm 162, it is machined to form a forearm having the desired configuration similar to the machining of a molded handguard. FIG. 17 schematically depicts a CNC machining center 184 that can be used to machine an unfinished forearm 162 to its desired final shape.

When forming the embodiment of FIGS. 10 and 11, unfinished forearm 162 is cut in half parallel with center line 164. The general structure of mounting rails 82a-82c are formed by the extrusion process with slots 84 and other engagement surfaces of mounting rails 82a-82c being machined to meet final tolerances after the extrusion operation.

After machining the extruded forearm, it is tumbled in a ceramic media for deburring, then cleaned and provided with a surface finish in same manner as a molded forearm as discussed above. Once the surface of the forearm has been given the desired finish, the forearm is completed can be assembled in a firearm 30.

Extruded and molded forearms will generally be machined and finished in the same manner. The configuration of the forearm, however, may make it more suitable for one process or the other. For example, tapered forearms, such as 70, 70a shown in FIGS. 1, 2, 5 and 6, are more easily molded while forearms having a cross section, taken transverse to centerline 64, that remains relatively constant over the axial length of the forearm, such as those shown in FIGS. 3, 7-10 and 14, are more suitable for extrusion.

In this regard, it is noted that both types of forearms can be formed using either process. However, if a tapered forearm is extruded, a substantially amount of material would have to be removed by machining thereby significantly impacting the efficiency of the process. The molding of a tubular forearm well suited for extrusion would not present undue inefficiencies, however, even greater efficiencies will generally be obtainable by extruding such forearms.

For both molding and extrusion processes, the unfinished forearm resulting from the molding or extrusion process reduces the amount of machining required and will generally give the forearm its final profile. The forearm is then machined to meet the desired final tolercances. After the machining, the forearm is plated using an electroplating or electroless plating process to protect the magnesium material from corrosion such as galvanic corrosion. The plating layer can function as the final finish layer of the forearm or a surface finish, such as an oven-baked ceramic coating, can be applied over the plating layer to give the product its final finish and color.

It is noted that the finished forearm may be used in the assembly of a new firearm 30 or be supplied as an aftermarket part. When supplied as an aftermarket part, the forearm allows owners of pre-existing firearms 30 to remove the original forearm, such as an aluminum or plastic forearm, and replace it with a forearm in accordance with the present disclosure.

While the present invention has been illustrated and described in the context of a handguard/forearm for an AR-style rifle, the present invention may be utilized with other firearm components, such as scope rings, butt stocks, grips and the like and with firearm components for other styles of firearms. The invention is not limited to the exemplary design described herein and the present invention may be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles.

Number	Date	Country
61863195	Aug 2013	US
61846674	Jul 2013	US
61735254	Dec 2012	US

MAGNESIUM FIREARM FOREARM AND METHOD OF MANUFACTURE

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CROSS REFERENCE TO RELATED APPLICATIONS

Provisional Applications (3)