Abstract:
A semiautomatic handgun includes various unique features to facilitate rapid, accurate shooting. Some examples of the handgun include a more compact recoil spring system, locating the recoil spring around the barrel while permitting rearward movement of the barrel in conjunction with the slide. Other examples include an automatic magazine release for releasing the magazine upon the discharge of the last cartridge in the magazine. Still other examples include a grooved or roughened top slide surface for facilitating slide manipulation with one hand. Further examples include auxiliary sight systems to facilitate determining the proper distance by which to lead a moving target. Other examples include a takedown tool stored within the handgun.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. provisional patent application No. 61/637,800, which was filed on Apr. 24, 2012, and entitled “Semiautomatic Firearm.” 
    
    
     TECHNICAL FIELD 
     The present invention relates to semiautomatic firearms. More specifically, a semiautomatic firearm having unique features to facilitate fast, accurate shooting is provided. 
     BACKGROUND INFORMATION 
     Semiautomatic firearms have been in use for over a century, and are popular for military, law enforcement, defensive, and sporting purposes. A semiautomatic firearm utilizes a reciprocating bolt or slide. Retraction of the slide upon discharging the weapon ejects the spent casing from the chamber. The slide then returns forward under spring pressure, carrying a fresh cartridge from the magazine into the chamber. The frame of a semiautomatic handgun typically includes an ejector for pushing the spent casing out of an ejection port in a predetermined direction. The slide typically includes a spring biased extractor having a hook for engaging the rim of a casing, permitting the casing to be extracted from the chamber in the absence of discharging a firearm. 
     It is necessary to control the retraction of the slide so that the slide does not retract a significant distance before the bullet exits the muzzle. While the bullet is being propelled forward within the barrel, gas pressure within the barrel is quite high. Excessive retraction of the slide at this time would direct at least some of this high gas pressure in undesirable directions, potentially endangering the shooter. Various mechanisms have been developed toward this end. 
     The simplest method of controlling slide retraction, commonly known as straight blowback, simply relies on gas pressure inside the casing to retract the slide. The mass of the slide, as well as the strength of the recoil spring, are selected so that the slide does not travel rearward a significant distance before the bullet exits the muzzle. This system is commonly used with small caliber semiautomatic handguns, up to and including 0.380 ACP. Because the barrel of such handguns is fixed, some handguns utilizing the system utilize a recoil spring that is coiled around the barrel, so that the barrel effectively serves as a recoil spring guide. Due to the increasing slide mass and recoil spring strength required with increasing pressure levels, this system is typically not utilized for handguns of 9×19 mm. caliber or higher calibers. 
     With increasing pressure levels, other mechanisms are necessary to ensure that significant slide retraction does not occur before the bullet leaves the muzzle, ensuring that gas pressure within the barrel has dropped to a safe level. A tilting barrel system is commonly used for this purpose. In such systems, the barrel is locked to the slide by either a projection that fits within the ejection port of the slide, or by a plurality of locking lugs that engage corresponding locking lugs on the interior of the slide. As the slide retracts, the barrel moves rearward with the slide for a short distance, before a pivoting link or lug on the bottom of the barrel causes the breech end of the barrel to pivot downward, disengaging with the slide, and allowing the slide to continue to retract independently. All such systems which are known to be present inventors utilize a recoil spring assembly that is adjacent to the barrel, thereby occupying additional space that could otherwise be occupied by additional devices. 
     Another means of ensuring that the barrel and slide do not disengage prematurely is a gas retarded blowback system, such as that used within the Heckler &amp; Koch P7 pistol. This system is similar to a straight blowback design, but utilizes a vent within the barrel to direct gas into a cylinder that contains a piston. When the pistol is discharged, the piston applies forward pressure to the slide until the bullet exits the muzzle, thereby resisting premature slide retraction. This mechanism results in reduced felt recoil, contributing to the accuracy with which the firearm may be shot. This mechanism also permits the recoil spring to be coiled around the barrel. However, this system is difficult to manufacture, and can in some instances result in excessive heat buildup within the firearm. 
     Other systems for controlling the movement of the slide include the falling locking block design of the Beretta 92F pistol, which provides for in-line movement of the barrel. This in-line barrel movement enhances the accuracy of the pistol. However, the locking block is subject to wear. The recoil spring of this pistol is located underneath the barrel, thereby adding bulk to the overall design. 
     Accordingly, there is a need for a system that controls the movement of the slide with respect to the barrel, wherein the recoil spring is coiled around the barrel, and avoiding the disadvantages of gas retarded blowback designs. Such a system would reduce the weight and bulk of the firearm, particularly when lights, laser aiming devices, or other accessories are secured to the dust cover of the frame, located in front of the trigger guard and below the barrel. 
     Sighting systems for handguns generally fall within two types. Iron sights typically consist of a post adjacent to the muzzle, which is aligned with a rear sight in the form of a U-shaped notch, V-shaped groove, or aperture. Iron sights may in some instances include various features to improve visibility, such as coloring, dots, fiber optic inserts, and/or tritium inserts. Iron sights are simple, generally durable, and compact. However, they often provide no indication of the proper lead for hitting a moving target. 
     Optical sighting systems, such as those using illuminated dot reticles, display an illuminated dot or other shape that is placed over the target when looking through the sight. Some optical sights provide a means of estimating lead for hitting moving targets. However, such sights add bulk and weight to a firearm. Particularly in the case of a handgun, such sights can increase the difficulty of carrying the handgun, particularly if concealment is important. Furthermore, such sights are often dependent upon batteries or other illumination means such as tritium. In the case of iron sights, if the tritium inserts go dim, the iron sights themselves are still useful. However, in the event of a battery powered or tritium powered optical sight, if the battery dies or the tritium goes dim, the sight is significantly less useful. 
     Accordingly, there is a need for a sighting system that combines the simplicity, ruggedness, and compactness of iron sights with a means of estimating lead when shooting at a moving target. Moving targets are common in both sporting and practical shooting applications, making a means of lead estimation particularly useful. 
     Many shooting situations in both sporting and practical contexts require the ability to manipulate the firearm with only one hand, including not only aiming and trigger squeeze, but also reloading and malfunction clearance. Reloading and clearing a malfunction require the ability to manipulate the slide. When working with only one hand, for example, in the case of a real or simulated injury, a portion of the slide such as the rear sight, ejection port, or muzzle portion of the slide is generally engaged with the shooters belt, the heal of the shooters shoe, or a convenient nearby hard surface. 
     However, many presently available handguns do not include a convenient projection on the slide for use during one-handed slide retraction. While some rear sights include a vertical forward surface that is useful for engaging convenient objects to retract the slide, many popular rear sights include a sloped forward surface, making the rear sight difficult to hook. Furthermore, although some ejection ports, such as those on a 1911 handgun, are easy to engage, ejection ports that lock up with the barrel by receiving a portion of the barrel have little excess material for engaging convenient objects to retract the slide. Many handguns are not suited for slide retraction by pushing the muzzle end of the slide against a convenient object, and this method of slide retraction is typically only practiced with full-size 1911 handguns without full-length guide rods. While it is known to include an additional projection within the slide to aid in one hand manipulation, the very few presently available projections would limit the selection of compatible sights, as well as interfere with some older methods of malfunction clearance, such as wiping the hand across the top of the slide to clear a stovepipe malfunction. 
     Some users attempt to overcome the above-described deficiency by applying skateboard tape to the top of the slide. The application of skateboard tape results in cosmetic disadvantages, as well as the potential for the tape to wear or to lose adhesion. 
     Accordingly, there is a need for a handgun slide having a means of engaging a convenient surface to facilitate one-handed slide retraction without interfering with the selection of sights or with the user&#39;s preferred method of malfunction clearance. 
     Presently available semiautomatic handguns utilize a detachable box magazine that is held in place in one of two ways. The most common method is a catch engaging a hole defined within the body of the magazine. The catch is released utilizing a button that is reciprocally secured within the frame of the handgun, behind and slightly below the trigger guard, for actuation with the user&#39;s thumb. The design of the magazine release must balance the ease with which the magazine can be released intentionally with the need to avoid releasing the magazine unintentionally. These needs are typically balanced by the size of the magazine release button, the strength of the magazine release spring, and/or the placement of the magazine release button. Often, the magazine release button is placed so that slight rotation of the handgun within the user&#39;s hand is required to engage the magazine release with the shooter&#39;s thumb and release the magazine. Although this location minimizes the likelihood of accidental magazine release, it also slows the speed of reloading. Other presently available handguns utilize a magazine catch located at the base of the grip, sitting underneath the bottom of the magazine. Although this style of magazine catch is generally more secure, it is much slower to reload, and can make malfunction clearance significantly more difficult. 
     In the field of semiautomatic rifles, it is known to automatically eject a stripper clip from an M1 Garand rifle upon firing the last round within the magazine. However, the present inventors are unaware of any prior means of automatically releasing a box magazine from a semiautomatic firearm upon firing the last round within the magazine. Such a feature would significantly speed reloading not only by avoiding the need to depress the magazine release, but also by avoiding the need to shift the user&#39;s grip. The user would simply be able to focus on grasping and inserting the fresh magazine, and chambering the next cartridge. 
     Shooters involved in stressful situations, whether competition or life and death struggles, have been known to lose count of the number of cartridges remaining within their magazine. With most semiautomatic firearms, determining the number of cartridges remaining in a magazine requires removal of the magazine, which may be undesirable depending on the anticipated immediacy with which the firearm may be needed. At least one semiautomatic handgun, known as the ASP, attempted to address this need with transparent grip panels, permitting the shooter to determine the number of cartridges remaining by looking at the side of the pistol. However, in poor light conditions, determining the number of cartridges remaining is still potentially difficult. Accordingly, a means of determining the number of cartridges remaining within a magazine, even in poor light, is desired. 
     SUMMARY 
     The above needs are met by various examples of semiautomatic handguns according to the present invention. One example of the semiautomatic handgun includes a recoil spring that is coiled around the barrel, along with a barrel that is structured to move rearward with the slide for a predetermined distance. Upon moving for the predetermined distance, the barrel disengages from the slide, permitting the breech face of the slide to separate from the chamber. 
     Another example of the semiautomatic handgun utilizes a magazine release that automatically releases the magazine from the handgun upon the discharge of the last cartridge in the magazine. 
     Another example of the semiautomatic handgun includes a slide having a grooved or roughened portion of its top surface to facilitate manipulation of the slide with one hand. 
     Yet another example of the semiautomatic handgun includes a sight system along the side of the handgun. This sight system is intended to facilitate estimating the correct distance by which to lead a moving target. 
     A further example of the semiautomatic handgun includes a magazine having a visibility indicator secured to the follower, and a slot defined within the side of the magazine so that the visibility indicator may be viewed. The grip of the semiautomatic handgun has a slot defined therein, corresponding to the slot within the side of the magazine. The visibility indicator within the magazine follower may therefore be viewed by the shooter to gain an approximate idea of the number of cartridges remaining in the magazine. 
     These and other aspects of the various embodiments of the semiautomatic firearm will become more apparent through the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a right side elevational view of a semiautomatic handgun. 
         FIG. 2  is a partially cutaway right side elevational view of a semiautomatic handgun. 
         FIG. 3  is a partially cutaway right side elevational view of a semiautomatic handgun. 
         FIG. 4  is a right side elevational view of a semiautomatic handgun. 
         FIG. 5  is a right side elevational view of a semiautomatic handgun. 
         FIG. 6  is a left side elevational view of a magazine for a semiautomatic handgun. 
         FIG. 7  is a right side elevational view of a magazine for a semiautomatic handgun. 
         FIG. 8  is a right side elevational view of a semiautomatic handgun. 
         FIG. 9  is a perspective view of the magazine release components of an example of a semiautomatic handgun, showing these components interacting with a magazine on which the follower is depressed. 
         FIG. 10  is a perspective view of the magazine release components of  FIG. 9 , showing these components interacting with a magazine on which the follower in its uppermost position. 
         FIG. 11  is a top plan view of a magazine and magazine follower for a semiautomatic handgun. 
         FIG. 12  is a top plan view of another example of a magazine for a semiautomatic handgun. 
         FIG. 13  is a left side elevational view of a magazine for a semiautomatic handgun, showing a magazine ejection spring deactivated. 
         FIG. 14  is a left side elevational view of a magazine for a semiautomatic handgun, showing a magazine ejection spring compressed. 
         FIG. 15  is a left side elevational view of a magazine for a semiautomatic handgun, showing a magazine ejection spring upon ejecting the magazine. 
     
    
    
     Like reference characters denote like elements throughout the drawings. 
     DETAILED DESCRIPTION 
     As used herein, terms such as “upper,” “lower,” “above,” “below,” etc. are used for convenience only, and refer to the normal orientation of the components. Such terms are not intended to be limiting with respect to components that may be oriented in different orientations. Referring to  FIG. 1 , an example of a semiautomatic handgun  10  is illustrated. The handgun  10  includes a frame  12  that houses the action, in a manner that is well understood to those skilled in the art. The frame  12  includes a grip portion  14 , which in some examples may have a pair of grip panels  16  removably secured thereto. In the drawings, only the right side grip panel  16  is illustrated, with the left side grip panel being essentially a mirror image. The frame  12  includes an action housing portion  18  at the top and of the grip portion  14 , and a trigger guard  20  in front of the action housing portion  18 . The top portion of the frame  12  includes a pair of slide rails (not shown, but well understood to those skilled in the art) for receiving a reciprocating slide (described below). The forward portion of the frame  12  includes a dust cover  22  which, in the illustrated example, includes a universal rail  24 , such as a Picatinny rail or other commonly used rail, for mounting various accessories such as lights and/or lasers. A trigger  26  is reciprocally mounted towards the rear of the trigger guard  20 , and is biased towards a forward position, in a manner that is well understood to those skilled in the art. Similarly, a magazine release  28  is reciprocally mounted within the frame  12  behind the trigger guard  20 , and is biased towards the left side of the frame  12 , in a manner that is well known to those skilled in the art. A grip safety  30  may optionally be included in the upper rear portion of the grip portion  14  of the frame  12 . As understood by those skilled in the art, the grip safety  30  is biased towards a rearward position, and resists rearward movement of the trigger  26  until the grip safety  30  is pushed forward by the shooter&#39;s grip. Depending on the specific action type of the semiautomatic handgun  10 , the frame  12  may further include a slide stop, a manual thumb safety, and/or a decocking lever, all of which are well understood to those skilled in the art. Also depending on the specific action type, the upper rear portion of the frame  12  may include a hammer, which is well known to those skilled in the art. 
     The handgun  10  also includes a slide  32  that includes a pair of rails that correspond to the slide rails of the frame  12 . The slide is reciprocally mounted on the slide rails in a manner that is well known to those skilled in the art. The slide  32  includes a forward portion  34  and a rear portion  36 . The forward portion  34  surrounds the barrel  38 , and defines a muzzle opening  40  supporting the muzzle end  42  of the barrel  38 , and an ejection port  44  adjacent to the chamber portion  46  of the barrel  38 . The rear portion  36  contains, depending on the type of action, either a striker or a firing pin, both of which are well understood to those skilled in the art. The rear portion  36  also includes an extractor, which may either be internal or external, and which is well understood to those skilled in the art. 
     The rear portion  36  includes grasping grooves  48  to provide traction between a user&#39;s hand and the slide during retraction of the slide. The unique grasping grooves  48  illustrated in  FIG. 1  are located not only along the sides  50  of the slide  32 , but also across the top  52  of the slide  32 . Although grasping grooves are used in the illustrated example, checkering or other surface roughening may alternatively be used. This configuration of grasping grooves  48  is particularly useful in the event that the user must retract the slide with only one hand, either because of an injury or as may be required during a training exercise or a stage in a competition. The user may engage the grasping grooves  48  disposed on the top  52  of the slide  32  utilizing the shooter&#39;s belt, the heal of the shooter&#39;s shoe, or any physical structure which may be conveniently located at the time that the slide must be retracted. The shooter, whose hand will be wrapped around the grip frame  14 , may then push forward on the grip frame  14  while maintaining the engagement of the grasping grooves  48  with whatever reasonably fixed surface may have been convenient at the time, thereby causing the slide  32  to move rearward relative to the frame  12 . This unique configuration of grasping grooves  48  therefore provides a means of retracting the slide with only one hand, without placing any restrictions on the style of rear sight (discussed below) selected, and without placing a structure on the slide  32  that could potentially interfere with reholstering the handgun  10 . Furthermore, if the shooter prefers to clear “stovepipe” malfunctions (in which a spent shell casing is trapped between the barrel  38  and slide  32 , within the ejection port  44 ) by wiping a hand across the top  48  of the slide, the grooves  48  will not interfere with this action. 
     Referring to  FIGS. 2-3 , additional details of the barrel  38 , slide  32 , and recoil spring  54  are shown. The recoil spring  54  is coiled around the barrel  38 , abutting a front  55  of the slide  32  at one end, and abutting a spring stop  57  secured to the frame  12  at its other end. The recoil spring  54  thereby utilizes the barrel  38  as a recoil spring guide rod instead of having a separate recoil spring guide rod below the barrel. This design reduces the weight of the handgun  10 , and also permits the dust cover  22  and rail  24  to be disposed higher on the handgun  10 . However, unlike previous designs which utilize a recoil spring coiled around the barrel, the handgun  10  utilizes a tilting barrel mechanism in order to ensure that the slide  32  and barrel  38  do not separate until a bullet has exited the muzzle  42 . Although the illustrated example of a handgun  10  utilizes a chamber and  46  of the barrel  38  that fits within the ejection port  44  in order to ensure that the barrel  38  and slide  32  move rearward together, interconnecting barrel and slide lugs such as those used on 1911 style pistols may also be used. 
     In the example of  FIG. 2 , the barrel  38  includes at least one lug  56  extending below the chamber portion  46 . A link  58  is pivotally secured between the lug  56  and the frame  12 . In the illustrated example, the link  58  is pivotally secured to the frame by a pin  60  formed as a part of the slide stop  62 , in a manner that is commonly used on 1911 style pistols. In this example, when the handgun  10  is fired, the link  58  permits the barrel  38  to travel rearward a short distance with the slide  32 , before pulling the barrel  38  downward and out of engagement with the slide  32 . 
     In the example of  FIG. 3 , the chamber portion  46  of the barrel  38  includes a downwardly depending lug  64  having an angled rear surface  66 . The frame  12  includes a corresponding engagement  68 , having a similarly angled forward surface  70 . When the handgun  10  is discharged, the barrel  38  and slide  32  again move rearward together, until the surface  66  of the lug  64  comes in contact with the surface  70  of the lug  68 . At this point, the mating surfaces  66 ,  70  guide the barrel  38  downward out of engagement with the slide  32 , permitting the slide  32  to travel rearward without the barrel  38 . Although a tilt barrel mechanism is illustrated, the use of a spring stop  57  as described above will allow the use of a falling locking block mechanism. In each case, the recoil spring  54  will provide appropriate resistance to rearward movement of the barrel and slide, both before and after disengagement of the barrel and slide. 
     Referring to  FIG. 6-7 , an improved magazine  98  is illustrated. The magazine  98  functions much like standard magazines, having a generally tubular body  100  that is closed at its lower end (by a removable baseplate  108  in the illustrated example), and open at its upper end. The upper end  109  includes a pair of feed lips  111  that are structured to hold cartridges within the magazine  98 , as well as to assist in guiding cartridges into the chamber of the barrel. A follower  110  is slidably secured within the body, and is biased upward by a spring (not shown, and well known to those skilled in the art) disposed between the follower and the closed lower end. A hole  107  is defined within one side of the body for engaging the magazine release  28 . 
     The improved magazine  98  includes a means for providing a shooter with information about the approximate number of cartridges remaining in a magazine. A magazine  98  is illustrated in  FIGS. 6-7 . The magazine body  100  defines a pair of side walls, with the left side wall  102  visible in  FIG. 6 , and the right side wall  103  being shown in  FIG. 7 . The magazine body  100  further includes a front wall  104  and back wall  106 . A follower  110  is reciprocally secured within the body  100 , and is biased upward by a spring (not shown, but well understood to those skilled in the art. A slot  112  is defined within the left side wall  102 , and a slot  113  is defined within the corresponding right side wall  103 . The follower  110  includes a visibility element  114  that is structured to be visible through the slots  112 ,  113 . The visibility element  114  may be a polished metal surface such as that shown in  FIG. 6 , or a tritium filled insert as shown in  FIG. 7 . 
     Referring to  FIG. 8 , each of the grip panel  16  includes a means for viewing the slot  112  or  113 . In the illustrated example, a slot  116  is provided within the grip panel  16 , corresponding to the slots  112  or  113  of the magazine  98 . The slot  116  may be empty, or may include a transparent or translucent panel therein, made from polycarbonate, acrylic, or other suitable plastic. Alternatively, the grip panels  16  may be made from transparent or translucent plastic. A shooter viewing the side of the grip portion  14  of the frame  12  will be able to observe the position of the visibility element  114  within the magazine follower  110 , and will thereby learn the approximate position of the follower  110  within the magazine  98 . If the follower  110  is relatively high within the magazine  98 , the shooter will know to plan to reload soon. Conversely, if the follower  110  is relatively low within the magazine  98 , as illustrated in  FIG. 8 , the shooter will know that reloading is not necessary. Particularly in the case of a tritium insert, the visibility element  114  permits the shooter to learn the approximate number of cartridges within the magazine  98  in poor light conditions. 
     Referring to  FIGS. 2-3  and  9 - 15 , a mechanism for automatically ejecting a magazine after the last round in the magazine is fired is illustrated. Most presently available semiautomatic handguns include a slide stop  64  that is structured to engage the follower within the magazine after the last cartridge within the magazine is loaded into the chamber. When the handgun is discharged and the slide moves rearward, upward pressure created by the magazine spring on the follower pushes the slide stop  64  upward, into the path of the slide  32  as the slide  32  returns forward under pressure from the recoil spring  54 . When the slide  32  engages the slide stop  62 , further forward movement of the slide  32  is resisted by the slide stop  62 . 
     In some examples of the handgun  10 , an automatic release mechanism  72  is operatively connected to the magazine release  28 . The automatic release mechanism  72  either operates in conjunction with the slide stop  62 , or may include a completely separate mechanism. When the last cartridge within the magazine is loaded into the chamber and is discharged, either the upward pressure of the magazine spring and/or the reciprocating motion of the slide  32  may be utilized to actuate the magazine release  28 , causing the empty magazine to automatically drop free from the handgun  10 . The shooter therefore does not need to worry about engaging the magazine release  28 , and needs only to focus on grabbing a fresh magazine, inserting the fresh magazine into the handgun  10 , and chambering the first cartridge from the fresh magazine. Once the magazine release is actuated, the magazine release mechanism is disengaged until the next magazine is emptied, so that a new magazine may be inserted and retained by the magazine release. 
     In some examples of the handgun  10 , the automatic magazine release mechanism may be selectively engaged or disengaged by the shooter. The mechanism may be disengaged by locking the mechanism components into place, and/or by disengaging the operative connection with either the slide stop and/or with the magazine release. A shooter competing in a competition having rules against the use of an automatic magazine release, or a soldier operating well away from sources of supplies who may wish to retain magazines, therefore has the option of either utilizing or disengaging the automatic magazine release mechanism. 
     Referring specifically to  FIGS. 9-11 , one example of an automatic magazine release  120  is illustrated. The automatic magazine release  120  includes a magazine release actuator  122 , having a top end  124  disposed adjacent to the slide stop  126 . The top end  124  of the magazine release actuator  122  includes a lug  127  that is structured to engage a follower  128  of the magazine  130 . The bottom end  131  defines a ramped surface  132  that is structured to engage a corresponding ramped surface  134  defined on the magazine release  28 . Although the illustrated example shows the actuator  122  operating separately from the slide stop  126 , those skilled in the art will recognize from the description herein that the actuator  122  could be operatively connected to the slide stop  126  so that the raising of the slide stop  126  will also raise the actuator  122 . The operative connection between the actuator  122  and follower  128  can therefore be established either directly or indirectly through the slide stop  126 . 
       FIG. 9  shows the position of the magazine release actuator  122  whenever the firearm  10  does not contain a magazine  130 , or a loaded magazine  130  is in place. Once the last cartridge in the magazine  130  is fired and ejected, the follower  128  engages the lug  127 , raising the magazine release actuator  122  at the same time as it raises the slide stop  126 , to the position of  FIG. 10 . As the magazine release actuator  122  moves from the position of  FIG. 9  to the position of  FIG. 10 , the ramped surface  132  engages the ramped surface  134 , moving the magazine release  28  from left to right, in the same manner as if the magazine release  28  had been engaged by the users thumb. The right side of the magazine release  28  engages the notch  107  in the magazine  130  to retain the magazine  130  within the firearm  10 . Movement of the magazine release  28  from left to right will disengage the magazine release  28  from the notch  107  to release the magazine  130 , causing it to drop free from the pistol  10 . Once the magazine  130  is released, the spring of the magazine release  28  returns the magazine release  28  to its default position, causing the corresponding ramped surfaces  132 ,  134  to bring the magazine release actuator  122  back to the position of  FIG. 9 . An additional spring biasing the magazine release actuator  122  downward may also be used for this purpose if desired. 
       FIG. 11  illustrates an example of a follower  128  that permits the selective activation or deactivation of the automatic magazine release  120 . The follower  128  includes a paddle  136  that is pivotally secured to the follower  128  by the pivot  138 . When the paddle  136  is in the position shown in  FIG. 11 , it will strike the lug  127  of the magazine release actuator  122 . Pivoting the paddle  136  away from this position will deactivate the automatic magazine release  120 . 
       FIGS. 12-15  illustrate another example of an automatic magazine release  140 . The automatic magazine release  140  includes all of the components of  FIGS. 9-10 , with the additional components described below. While the example of  FIGS. 9-10  depends on balancing the strength of the magazine spring with the strength of the magazine release spring so that the magazine spring will have sufficient strength to actuate the magazine release through the movement of the actuator  122 , the example of  FIGS. 12-15  utilizes a separate release actuator spring assembly  142  to bias the actuator  122  upward. The spring assembly  142  is contained within a tube  144  defined within, or outside of the magazine  146 . The tube  144  contains a spring  148 . A base  150  is disposed below the spring  148 . The base  150  includes a lug  152  that is structured to fit within a channel  154 . The channel  154  includes a lower end  156 , and an upper end  158  at which a ledge  160  is defined. When the base  150  is within the lower end  156  of the channel  154  ( FIG. 13 ), the spring  148  is uncompressed, and the spring assembly  142  is therefore deactivated. Pushing the base  150  upward so that the lug  152  rests on the ledge  160  compresses the spring  148  ( FIG. 14 ), thereby activating the spring assembly  142 . In some examples, the channel  154  may be defined so that the lug  152  penetrates the channel  154  so that a shooter may manipulate the base  150  by pushing upward or downward on the lug  152 . In other examples, the channel may not penetrate completely through the tube  144 , so that a tool may be inserted into the bottom of the tube  144  to manipulate the base  152 . 
     A head  162  is disposed above the spring  148 . The head  162  includes an engagement surface  164  about its lower periphery. The upper end  166  of the head  162  is structured to engage the lug  127  of the actuator  122 . A lever  168  is pivotally secured at pivot  170  to the tube  144 . The lever  168  includes a follower engaging end  172  and the head engaging end  174 . The lever  168  is typically positioned as shown in  FIGS. 13-14 , with the head engaging end  174  engaging the surface  164  of the head  162  to hold the head  162  within the tube  144 . As the follower  129  strikes the follower engaging end  172  ( FIG. 15 ), as it would when the follower  129  rises to its uppermost position, the lever  168  pivots so that the head engaging end  174  disengages from the head  162 , allowing the head  162  to strike the lug  127  of the actuator  122 , thereby releasing the magazine  140 . Some examples of the lever  168  may be spring biased towards the position of  FIGS. 13-14 . 
     Those skilled in the art will recognize that a base having a fixed position may be substituted for the base  150 , and that the follower  128  may be substituted for the follower  129 . In this case, activation or deactivation of the automatic magazine release mechanism would be by movement of the paddle  136  rather than the base  150 . 
     Referring back to  FIGS. 2-3 , in the event that a disassembly tool  74  is required either for routine disassembly for cleaning, or detailed disassembly, the disassembly tool  74  may be stored within the handgun  10 . In the illustrated example of the handgun  10 , the disassembly tool  74  is stored within a receptacle  76  defined within a lower rear portion of the grip portion  14  of the frame  12 . Other examples of the handgun  10  may store the disassembly tool  74  in other locations, for example, in other locations within the grip portion  14 , or other locations on the frame  12 . 
     Referring to  FIGS. 4-5 , a unique sight configuration is illustrated. The handgun  10  includes a conventional front sight  78  and rear sight  80 , which may be of any conventional type. The front sight  78  and rear sight  80  may in some examples be secured to the top  52  of the slide  32  in a manner that permits replacement with alternative front and/or rear sights, using any presently used arrangement which is known to those skilled in the art (dovetail cuts, etc.). These sights are intended to be used in a conventional manner, and are therefore not further described. However, additional sights are provided along each side  50 . These additional sights are used with the handgun held in a conventional substantially vertical orientation, and provide a horizontal offset from the conventional point of aim. These sights may therefore be used when estimating the distance by which to lead a moving target. Hitting a moving target requires taking into account the speed at which the target is moving relative to the reaction time of the shooter, the mechanical time between pulling the trigger and firing the gun, and the time required for the bullet to travel to its target. The shooter will therefore generally aim a short distance ahead of the target, rather than directly at the target. Determining the correct lead, or distance ahead of the target to aim, is largely a function of skill and experience, but can be simplified by lead-estimating sighting devices. 
     Referring to  FIG. 4 , a lengthwise channel  82  is defined within each side  50  of the slide  32 . The structures described herein are illustrated on the right side of the handgun  10 , but the left side of the handgun  10  is a mirror image of the right side. A front sight  84  is disposed within a forward portion of the channel  82 , relatively close to the muzzle  42 . A rear sight  86  is disposed in a rear portion of the channel  82 , in proximity to the rear sight  80 . The illustrated example of the front sight  84  and rear sight  86  are of a post front, U-notch rear configuration, but other configurations, for example, an aperture rear sight, or a V-notch rear sight combined with a rounded front sight, may be used. Regardless of the sight configuration used, the front sight  84  and rear sight  86  will, in some examples, be contained entirely within, or will not substantially protrude outward from, the channel  82 . Avoiding substantial protrusion of the sights  84 ,  86  from the channel  82  resists interference of the sights  84 ,  86  with standard holsters. The sights  84 ,  86  may optionally include tritium inserts, fiber optic inserts, colored surfaces, gold beads, or other visibility enhancements which are well known to those skilled in the art. 
     Referring to  FIG. 5 , an alternative additional sight configuration is illustrated. In this configuration, a lengthwise channel  88  extends from the rear face  90  of the slide  32 . In the illustrated example, the channel  88  extends to a position in proximity to, but rearward of, the ejection port  44 . Depending on the configuration of the slide  32 , other lengths for the channel  88  may be used. A forward visibility enhancer  92  is placed at the forward end of the channel  88 , effectively forming a front sight, so that the forward visibility enhancer  92  may be viewed by the shooter while looking at the slide&#39;s rear face  90 . At least one other visibility enhancer is disposed at the rear of the channel  88 , effectively forming a rear sight, so that it may be viewed by a shooter looking at the slide&#39;s rear face  90 . In the illustrated example, a pair of rear visibility enhancers  94 ,  96  are placed above and below the channel  88 , respectively. Preferred visibility enhancers  92 ,  94 ,  96  are tritium inserts, but other visibility enhancers, such as fiber optic tubes, colored dots, or gold beads may alternatively be used. A shooter may align the additional sight of  FIG. 5  by visually aligning the visibility enhancers  92 ,  94 ,  96  so that they form a vertical line, with equal space between the visibility enhancers  92 ,  94 ,  96 . 
     A shooter may therefore selectively use either the conventional sights  78 ,  80  to engage stationary targets or some moving targets, or may elect to use the additional sights of  FIGS. 4-5  to engage moving targets. When the sights  84 ,  86  or the visibility enhancers  92 ,  94 ,  96  are aligned, the dimensions and locations of the sights  84 ,  86  or the visibility enhancers  92 ,  94 ,  96  relative to each other will be selected to indicate a point that is horizontally offset from the normal point of aim. This horizontal offset can assist the shooter in determining the proper distance by which to lead a moving target in order to hit that target. 
     The present invention therefore provides a handgun having unique improvements over prior handguns. Some examples of the handgun  10  include an improved cycling mechanism combining the advantages of a tilt barrel system with the compactness of a recoil spring that is wrapped around the barrel. Other examples of the handgun  10  include an automatic magazine release that is actuated upon discharge of the last cartridge in the magazine, thereby speeding the reloading process. Still other examples of the handgun  10  include a disassembly tool stored within the handgun  10 . Further examples of the handgun  10  include grasping grooves on top of the slide as well as along the sides of the slide, thereby facilitating manipulation of the slide with only one hand, and without limiting rear sight design. Still other examples of the handgun  10  include sight systems along the sides of the handgun  10  to facilitate the determination of the proper distance by which to lead a moving target. Further examples of the handgun  10  provide a means of determining an approximate number of cartridges within the magazine without removing the magazine, even in poor lighting conditions. 
     A variety of modifications to the above-described embodiments will be apparent to those skilled in the art from this disclosure. Thus, the invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The particular embodiments disclosed are meant to be illustrative only and not limiting as to the scope of the invention. The appended claims, rather than to the foregoing specification, should be referenced to indicate the scope of the invention.