Abstract:
A forward hand guard assembly for a rifle includes an upper metal hand guard which is secured to the receiver rifle by a clamp, and a lower grip which is releasably secured to the upper guard and the clamp by a latching pin. The clamp has a locking mechanism which can be released without tools. The grip is a molded plastic body designed to rest comfortably in the hand.

Description:
This application claims benefit of provisional application 61/510716, filed Jul. 22, 2011. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to a forward hand guard assembly for a semiautomatic rifle, such as the AR-15 rifle illustrated in  FIG. 1 . 
     The polymer forward hand guards or “forearms” provided as original equipment on many rifles are of large diameter and tubular in design requiring that the shooter&#39;s hand be wrapped around the guard (substantially beyond 50% of the circumference of the tube, as shown in  FIG. 3   b ) to get a secure grip. Gripping a large diameter forearm this way is not ergonomic; it tires the hand and lower arm, which results in a poor grip and muscular fatigue.  FIGS. 2   b  and  2   c  illustrate that the human hand is better suited to grip small diameter cylindrical objects where the fingers and hand can wrap fully around the diameter of the cylinder (locking the cylinder between the fingers and palm); while  FIG. 2   a  shows the hand in an even more ideal position in the fully relaxed open position.  FIG. 3   a  shows a handgrip according to the present invention: the hand is relaxed, in a configuration more like that of  FIG. 2   a.    
     Unlike hunting or other military rifles which use a full stock, many semiautomatic rifles use three separate primary human interface points for stability, control and operation: the butt stock, the grip and the forward hand guard. The butt stock is used to ground the weapon against the body of the shooter, providing a point of stability; it also transfers recoil away from the weapon. The grip, sometimes referred to as a pistol grip, is a second point of control and stability for the weapon, and optimally positioning the shooter&#39;s trigger finger near to the weapon&#39;s operational controls. The forward hand guard serves as the third interface between the shooter and the weapon and is a primary point of support and control for weapon aiming. 
     The forward hand guard provides the main point of support for stabilizing the weapon by the shooter, allowing for accurate aiming and firing. Thus the hand and arm that interact with the forward hand guard are often referred to as the “support side” of the shooter, while the trigger hand is referred to as the strong or dominant side. 
     When a rifle is raised to the dominant side shoulder and aimed perpendicular to the shooter&#39;s body, the weight of the elevated stock, action or receiver, and barrel creates a cantilever effect, requiring a brace to counteract the weight and to stabilize the front of the weapon. The shooter&#39;s support side arm, with elbow bent and hand gripping the underside of the forward hand guard create the triangular brace needed to help transfer the outward extending weapon weight back to the shooter&#39;s body. Bracing the weapon in this manner also provides another point of stability for the weapon. 
     The act of extending the arm and hand out away from the body to support the weight of the rifle by gripping the forward hand guard, places physical demands on the shooter&#39;s anatomy. When the shooter is standing erect, the stability of the rifle becomes a function of a shooter&#39;s physical conditioning, technique, and comfort or ability to relax. Failure in any of these areas results in muscular fatigue, which commonly manifests itself through discomfort and shaking or quivering. Such movement is transferred to the rifle and compromises accuracy. 
     The fatigue created by the extension in arm and hand results in shaking or quivering of the muscles and causes movements in the weapon&#39;s barrel and sights, compromising accuracy. 
     The AR-15 rifle, M4 carbine, M16, AR-10 and like semiautomatic rifles share many common features and are all weapons that utilize the three separate primary human interface points described above. Because of the similarities in design and for the ease of this discussion we refer to this group of rifles simply as AR-15 rifles hereafter. 
     In the case of AR-15 type rifles, most are factory-equipped with one of three front hand guard designs: the traditional circular or oval polymer forward hand guard, an elongated tubular aluminum hand guard, or what is commonly referred to as an aluminum quad-rail hand guard. The purpose of these hand guards is (a) to provide a gripping surface for the shooter to secure the rifle, (b) to protect the forward hand from heat radiated from the barrel, and (c) to protect the operating components of the rifle. One feature that nearly all of these forward hand guards have in common is that they are all designed to be centered about the center of the rifle barrel&#39;s bore or center line. 
     A second common feature of many of these designs is that they all seek to maintain proper thermal clearances away from the hot barrel resulting in relatively large diameter profiles. 
     The fact that most forward hand guards are centered around the barrel&#39;s bore means that their widest points correspond with the two outer most surfaces of the barrel (i.e., three and nine o&#39;clock positions). To maintain consistent insulating properties of the guard, the bottom of the guard or the six o&#39;clock position is at least as far from the center of the barrel as at the three and nine o&#39;clock positions. The combination of side width and the depth between the center of the barrel and the lowest point of the guard&#39;s profile require a deep grasp in order to properly secure the rifle with the support hand. 
     To grip these hand guards with a secure grip, the shooter must rest the bottom of the hand guard in the palm, while extending and wrapping fingers up and around the guard&#39;s large circumference. To achieve a secure grip, the ball of the shooter&#39;s finger tips must extend beyond 50% of the guard&#39;s circumference. The area above the 50% circumference can be referred to as the control surface area. It is this area that the fingers pull down against, capturing the guard between themselves and the palm. With the fingers positioned in this manner, having crossed beyond the 50% threshold, the forward hand sufficiently envelops the guard to provide a secure or locking grip. A locking grip is established when the fingers are able to pull an object in toward the palm. Conversely, if a shooter grips such guards over less than 50% of the circumference, with sufficient force, the guard will have a tendency to pop up out of the grasp of the shooter. This phenomenon is similar to what happens when one pinches a golf ball or other similar round object over less than 50% of the circumference. In such situations more force, only increases the likelihood of the guard jumping. 
     In addition to the general deep grasp problem described previously, aluminum quad rail guards are also hampered by the sharply machined “picatinny” accessory mounting rails that are machined into their side and bottom profiles. The harshness of the machined surfaces has resulted in manufacturers and aftermarket providers creating many after-the-fact solutions, the most common of which is the application of external covers that are meant to insulate the shooter&#39;s hand and to provide a smoother surface to grasp. The consequence to all these designs is that they all add even more circumference around which a shooter&#39;s hand must reach, further compounding the deep grasp problem. 
     Although physical conditioning and shooting technique are unique to each shooter, comfort can be directly influenced through proper ergonomic hand guard design. 
     The ideal hand guard design would provide a shallow grip, allowing for a relaxed hand and a positive gripping control edge to allow for a strong yet comfortable secure grip. These two ideal characteristics would be achieved by lowering the center of the guard&#39;s control surfaces from the barrel&#39;s center line, so that the guard is not constrained to the default widths and would also provide the room necessary to incorporate control edges for increased gripping. 
     The shallow grip used in an ideal hand guard profile would enable the shooter&#39;s hand to relax into a natural position. The universal natural position of a hand is a flat palm, semi-erect thumb and half-bent fingers. By incorporating a guard profile that allows for a relaxed natural hand position the stress on a shooter&#39;s forearm and hand is greatly reduced. Secondly, the ideal design would utilize well-defined, finite control edges as part of the shallow profile allowing the shooter to expend the minimum energy possible to maintain control of the weapon. 
     Because shooters and shooting conditions vary widely from one situation to the next, the ideal design would include various situation-specific hand grip profiles, and would allow these hand grip profiles to be quickly interchanged without the need for tools while in the field. Furthermore the tool-less assembly locking mechanism would provide a robust, secure function. 
     By creating a forward hand guard profile that allows the hand to relax and assume a natural position combined with control edges for an optimal secure grasp, a shooter will experience less fatigue and will allow for steadier and longer holds of the rifle. 
     It would improve the accuracy of a firearm, and the comfort of the shooter, to provide an ergonomic forward hard guard that overcame the problems mentioned above. 
     SUMMARY OF THE INVENTION 
     An object of the invention is to optimize the interface between the rifle and its shooter, in particular by providing a hand guard assembly having a replaceable lower grip portion which can be chosen for its ergonomic compatibility with a particular person&#39;s anatomy, stance, and shooting environment or situation, while maintaining the utility of readily mountable accessories. 
     These and other objects are attained by a forward hand guard assembly for a rifle, as described below. 
     The hand guard assembly includes an upper metal portion which provides structural strength and a lower ergonomic grip portion which permits a shallower grip and enables one to support the rifle with a relaxed hand. 
     The terms “longitudinal”, “transverse”, “horizontal” and “vertical” are use below to indicate directions relative to the rifle, if held normally and pointed in a horizontal direction. “Longitudinal” means along or parallel to the axis of the rifle barrel. “Transverse” means in a horizontal direction perpendicular to longitudinal. “Lengthwise” means in a longitudinal direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, 
         FIG. 1  is a side view of an AR-15 rifle, with a standard front hand guard; 
         FIG. 2   a  depicts a relaxed outstretched hand; 
         FIGS. 2   b  and  2   c  shows the hand tightly gripping a cylindrical object; 
         FIGS. 3 and 4  show the hand configuration when holding a rifle equipped according to the present invention, and according to conventional practice, respectively; 
         FIG. 5  shows a forward hand guard assembly embodying the invention, mounted on a rifle; 
         FIG. 6  is a perspective view of the hand guard; 
         FIG. 7  is an exploded perspective view thereof from the front, left side, and below; 
         FIG. 8  is an exploded perspective view thereof from the rear, right side, and above; 
         FIG. 9  is an exploded perspective view of a first modified form of the hand guard; 
         FIG. 10  is a rear elevation of the hand guard of  FIGS. 6-8 ; 
         FIG. 11  is a front elevation of the hand guard of  FIGS. 6-8 , mounted on a rifle; and 
         FIG. 12  is a view like  FIG. 11 , showing a second modified form of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A forward hand guard assembly embodying the invention is designated by reference  10  in  FIG. 3 , where it is shown positioned for mounting over the barrel of a rifle. Some firearms have a sight post at the end of or along the barrel which is too large for the assembly to fit over; therefore, the device is made in two halves which can be assembled around the barrel. 
     Referring to  FIGS. 6-10 , the two major components of the assembly are an upper metal portion  20  and a lower hand grip  40 . The parts have mating surfaces  22 ,  42  ( FIG. 7 ) which meet at a plane containing, or closely parallel to, the axis of the gun barrel. 
     The upper metal portion  20  is made of a single piece of metal, preferably aluminum, and provides most of the structural strength of the assembly. It has an integral Picatinny rail  24  extending lengthwise along its top surface, between two oblique walls  26 ,  26 ′ and two vertical side walls  28 ,  28 ′ ( FIG. 10 ). The integral rail is designed to align perfectly with the standard rail formed on the top of the AR-15&#39;s upper receiver, so the two provide a continuous surface for mounting optics and other accessories. 
     The outer surfaces of the oblique walls and the side walls are flat and parallel to the barrel axis. An array of holes  30  is formed in each of the oblique and vertical walls. Preferably, equally spaced holes are provided in each wall, to give the user the choice of a number of positions at which to mount auxiliary Picatinny rails. Threaded inserts  32  are permanently installed in the holes, to receive screws  33  ( FIG. 7 ) for retaining an auxiliary or modular Picatinny rail  34 . The preferred modular rails are symmetrical—so they are reversible if damaged and so they cannot be installed backwards. The modular Picatinny rails have rounded ends that allow for faster accessory changes in the field and better avoid snagging on foreign objects. The rails have flutes  35  on their back sides to ventilate the upper guard while maintaining adequate rail rigidity. 
     The upper metal portion has a number of slots  36  in both the oblique and vertical walls to provide good ventilation around the hot gun barrel, and to permit water, dust and other debris to drain through when necessary. 
     The hand grip  40  is preferably made of a moldable polymeric resin. The resin may be fiber reinforced, and is selected for qualities of strength, heat resistance and impact resistance. The presently preferred polymer is a polyamide resin such as nylon 66 or Zytel (Zytel is a trademark registered by DuPont). 
     The hand grip is shaped to provide a comfortable, ergonomic shape for the hand It preferably keeps the entire hand below the centerline of the barrel. The bottom  44  ( FIG. 10 ) of the grip is flat, smooth and uninterrupted, except for a lower track described below. The flat bottom makes the grip ideal for shooting from rest positions, such as from sandbags and ledges, and prevents the grip from catching on foreign objects. 
     A preferred form of the grip is shown in  FIGS. 6-10 . The grip has, on either side of the flat bottom surface, a pair substantially quarter-round convex surfaces  46  having a first radius R 1  ( FIG. 10 ). Each convex surface is tangent to the flat bottom surface  44 . 
     A pair of substantially quarter-round concave surfaces  48 , having a second radius R 2 , lie above the respective convex surfaces and meet the convex surfaces at an angle of about 90°, thereby defining gripping edges  50 . 
     Radii R 1  and R 2  are each between 0.5 and 1.0 inches. The gripping edge is rounded to a third radius R 3  much smaller than said first and second radii, 0.125 inch at most. 
     Preferably, the concave and convex surfaces are substantially cylindrical, and their longitudinal axes are parallel or slightly tapering to one another and to the gun barrel. 
     The grip&#39;s width is at least three inches—substantially greater than that of a standard forearm—and the gripping edges  50  are well below the barrel of the rifle. That is, the gripping edges are in a common plane which does not intersect the barrel. 
     Although the polymer is heat resistant, to further protect it from the hot gun barrel after prolonged firing, a metal heat shield  54  ( FIG. 7 ) is installed between the hand guard and the grip. When the shield is installed from the rear of the guard, its flanges  56  slide lengthwise into grooves  58  formed on the inner walls of the grip, and the heat shield cannot move once the grip is installed. In its installed position, the heat shield is radially spaced from both the barrel and the grip. Holes  60  in the heat shield allow ventilating air to pass and let water drain quickly if the hand guard assembly gets submerged. 
     A metal track  62  is molded or glued into the bottom surface of the hand grip. The track has a slot  64  which runs lengthwise and is shaped to receive standard accessories such as bipod rests: it has a slot with a “T” cross-section ( FIG. 6 ) and is open at one end. A keyhole opening  66  near the rear of the slot admits standard mount hardware. Two common standard channels are the Aschutz-type, which has a 0.400 inch opening and the Freeland type, which has a 0.330 inch opening. 
     The upper guard is secured to the rifle receiver by a clamp  80  at the rear of the assembly. The clamp is drawn toward the upper guard  20  by four set screws  82  which pass upward through vertical holes  84  in the clamp. Once the screws are tightened, the upper guard is rigidly secured to the rifle&#39;s barrel nut. The clamp and its screws are concealed, normally, by the grip. 
     The hand guard assembly is supported only at its rear, where it is clamped to the receiver of the rifle. With this so-called “free-floating” design, the hand guard assembly does not contact the barrel of the weapon at all, and thus avoids stressing or deflecting the barrel. Moreover, this design keeps the hand guard assembly thermally isolated from the barrel. It thus provides a thermally stable mounting platform for precision accessories such as optics and lasers, and an anchoring point for slings free from the barrel. The clearance between the barrel and the hand guard assembly should be made sufficient to accommodate gas piston systems, heavy match or target barrels, and both factory and aftermarket sights. 
     The grip is installed by sliding it rearward onto the upper grip. The forward end of the upper guard (see  FIG. 7 ) has two tabs  38  that extend toward one another, flush with the lower surface of the upper guard. These tabs normally seat in slots  74  formed in the sides of the grip, and hold the guard and the grip together; however, each slot is interrupted by a vertical opening  76  so that the parts can separate when the lower grip is moved forward with respect to the upper guard. 
     The clamp has a dovetail tenon  78  ( FIG. 8 ) running in the longitudinal direction parallel to the barrel, and the grip has a complementary dovetail groove  80  which slides onto the tenon from the front. Thus the tabs and the dovetail joint hold the upper guard and grip together at the front and rear, respectively, when the parts are assembled. 
     The preferred grip is locked in its assembled position by inserting a takedown pin  82  into a horizontal transverse hole  84  in the grip. When installed, the pin also passes through a horizontal transverse groove  86  in the clamp. The takedown pin is latched in its installed position by a detent pin  88  containing a coil compression spring that biases the detent pin toward the takedown pin. The latter has a surface indentation  94  in which the detent pin seats to prevent accidental loss of the takedown pin. 
     The takedown pin shown may be replaced (see  FIG. 9 ) by a pin  82 ′ which must be turned, rather than removed, to allow the grip to slide forward. The pin can be turned with a tool, or it could have a lever affixed to its end, which would eliminate the need for a tool. This pin remains in position; it is turned approximately 90° to align a cutout in the pin while allows the lower guard to slide forward freely without frictional resistance from the lower clamp. 
       FIGS. 11 and 12  show alternative grip geometries. One can see that in each case, the geometries provides gripping points below the barrel axis. 
     Each grip  40  may be quickly removed from the assembly without tools by removing the takedown pin; another hand guard of a different shape may be quickly substituted. The interchangeability of hand guards makes it easy and inexpensive to modify the rifle for different people, shooting stances, and situations. Therefore, a single upper guard  20  and a number of interchangeable grips may be assembled in a kit, not shown. 
     The invention was designed initially for AR-15 type rifles, but could be easily adapted to fit many other types of firearms. 
     Preferably, all the parts of the device are made of materials which are rust and corrosion resistant. While some preferences for materials of manufacture have been indicated, it should be understood that other materials may prove suitable, or even superior, and that the invention in its broadest sense is not limited to particular material selections. 
     Since the invention is subject to modifications and variations, it is intended that the foregoing description and the accompanying drawings shall be interpreted as only illustrative of the invention defined by the following claims.