Abstract:
Methods and apparatus are disclosed for a locked machine gun that includes a casing, a barrel, a locking breech mechanism, an abutment and a quick change attachment. The locking breech mechanism has at least one locking body. The abutment holds the locking body or locking bodies of the locked breech mechanism. The quick-change attachment is used to facilitate the removal of the barrel and insertion and attachment of a new barrel. A first part of the abutment remains on the casing when the barrel is being changed, and a second part of the abutment is firmly connected to the barrel. The quick-change attachment is equipped to bring about a separation between the first part of the abutment remaining with the casing and the barrel with the second part. Also, the second part of the abutment has a curved section which controls the engagement of the breech mechanism in the abutment when the breech mechanism closes.

Description:
RELATED APPLICATION 
   This patent is a continuation-in-part of International Patent Application Serial No. PCT/EP2003/005927, filed Jun. 5, 2003, the disclosure of which is incorporated herein by reference. 

   TECHNICAL FIELD 
   This disclosure generally relates weapons and, more particularly to methods and apparatus for use in a locked machine gun. 
   BACKGROUND 
   A locked machine gun includes locking parts on a breech mechanism and an abutment. These locking parts engage one another before the machine gun fires a shot. As will be readily appreciated, the locking parts are activated by the closing breech mechanism and, therefore, are abruptly subjected to stress. Additionally, the locking parts experience significant wear of tear because a machine gun may fire an extremely high number of rounds (at least some 10 5  rounds) during its life. 
   To account for this wear and tear, a conventional machine gun, such as the MG 42, uses an abutment that is coupled to a detachable barrel. When the barrel is worn out, it is scrapped along with the abutment. The movable locking parts that work with the abutment are associated with and coupled to the breech mechanism. Accordingly, these movable parts can be changed together with the breech mechanism and then, if necessary, be individually replaced in the armory. 
   Thus, the MG 42 has an advantage in that it is possible to change those wearing parts that are subjected to the most stress. On the other hand, a disadvantage is that the abutments are expensive to manufacture and they have to be changed in cases when only the barrel is worn out. Accordingly, there may be many instances in which the abutment is not worn out, but it must be replaced because the barrel of which the abutment is part is worn out. Further, abutment wear is not typically even. 
   The MG 42 is a recoil-operated gun with a removable barrel. With gas-operated machine guns, a gas piston facilitates the unlocking and loading motions, and the barrel remains rigid during the firing of a round. For this reason, the abutment in gas-operated machine guns is usually designed to be rigid in the casing of the weapon. Consequently, when replacing a worn abutment, the casing parts are also replaced. 
   Recoil-operated machine guns are also advantageous because it is easy to replace parts during use. If, for example, during the use of the weapon a quartz pebble falls into the abutment during the firing of a round, it is possible that the entire lock will no longer function. In the case of the recoil-operated MG 42, it is sufficient to change the barrel and if necessary the breech in order to make the MG fit for use again. The marksman can perform these activities on site in less than a minute. On the other hand, if a similar quartz pebble falls into the breech of a gas-operated MG, the weapon casing must be completely replaced. This cannot be performed in the field because the marksman of course does not carry a second weapons casing with him. 
   It is possible to assign the abutment to the barrel with the gas-operated MG, but the above mentioned disadvantages would still exist. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a side view of a conventional machine gun. 
       FIG. 2  is a partial longitudinal cross-sectional view through the example machine gun of  FIG. 1 . 
       FIG. 3  is front oblique view of the breech mechanism of the machine gun of  FIG. 2 . 
       FIG. 4  is a front oblique view of the bolt head of the breech mechanism of  FIG. 3 . 
       FIG. 5  is a perspective view of the locking block of the breech mechanism of  FIG. 3 . 
       FIG. 6  is a side view of the breech mechanism of  FIG. 3  prior to locking. 
       FIG. 7  is a side view of the breech mechanism of  FIG. 3  after locking and just prior to firing. 
   

   DETAILED DESCRIPTION 
   Throughout this specification, all directional references, e.g., “front,” “rear,” “up” etc. are with respect to the machine gun in a horizontal firing position, where the direction of fire is “to the front.” 
     FIG. 1  shows a conventional, light weight machine gun  10  with a barrel  12 , to which a barrel-changing device  14  is connected. The barrel-changing device  14  is the mechanism used to interchangeably hold the barrel  12  in a casing  16 . The casing  16  also includes a reloading device  18  such as a magazine, a butt  20  with a trigger  22 , and a rear stock  24 . A portion of the light weight machine gun  10  at which a rear end of the barrel  12  is located is shown generally at reference numeral  26 . 
     FIG. 2  reveals further detail of the area of  FIG. 1  referred to by numeral  26 . As shown in  FIG. 2 , the rear end of the barrel  12  is sectioned on a radial plane adjacent a center line  28  of the barrel  12 . Opposite the barrel  12  is the casing  16 . When the barrel  12  is inserted into the light weight machine gun  10 , an abutment area  30  is formed between the rear end of the barrel  12  and the casing  16 , which includes a recess  32  that is open to the front and forms a shoulder  34  to the rear having a smaller diameter than that of the abutment area  30 . Accordingly, the rear of the abutment area  30  is defined by a first part  36 , which includes the casing  16 , and the front of the abutment area  30  is defined by a second part  38  including the barrel  12 . 
   Although not shown in the drawings, the first part  36  includes openings into which a bolt head  44  (described below) can penetrate with two locking pegs  46 ,  48 . After the bolt head  44  is inserted through the openings in the first part  36 , the bolt head  44  is rotated to cause the locking pegs  46 ,  48  to engage the casing  16  to prevent rearward movement of the bolt head with respect to the casing  16  during firing. In particular, the locking peg  48  may engage the shoulder  34 . 
   The barrel  12  includes an extension  50  that protrudes from the rear of the barrel  12 . Accordingly, the second part  38  of the abutment  30  includes the extension  50  having a radial cam  52 . As described in detail below, the radial cam  52  cooperates with the bolt head  44  to facilitate locking of the bolt head  44  with the casing  16 . 
   As shown in  FIGS. 3 ,  6 , and  7 , a breech mechanism  60  includes the bolt head  44  and a bolt head carrier  62 . The bolt head carrier  62  is configured for straight-line movement of the bolt head  44  along the center line  28 . The bolt head carrier  62  is capable of straight-line movement with respect to the casing  16 . The bolt head  44  follows this movement, but rotates around center line  28  during the first phase of the backward movement and in the last phase of the forward movement. 
   To enable rotation, the bolt head  44  includes a sliding block  64 , which extends past the center line  28  into the bolt head  44 . The sliding block  64  rides within a crank  66 . The bolt head  44  includes a radial bore hole  66  for the purpose of holding said sliding block  64  in its position. The sliding block  64  includes a bore hole  76  to accommodate the firing pin. The bolt head  44  also includes an axial bore hole  70  that is penetrated by the firing pin that lies along the center line  28 . For removal of the sliding block  64  the firing pin must first be pulled out to the rear along the center line  28 , and then the sliding block  64  must be radially extracted from the bolt head  44  and from the crank  66 . 
   The contour of the crank  66  has, an extended z-shaped figure, with a rear end section, which extends parallel to the direction of the center line  28 , and with a middle section extending between the rear end section and a front section. These sections have upper and lower edges, which run generally parallel to one another. The upper and lower edges of the front and middle sections are shaped differently from one another. As shown in the drawings, the lower edge is a straight line in the front and middle sections, which connects to another straight line forming the lower edge of the rear section. The upper edge of the rear section extends parallel to the center line  28 . The upper edge of the middle section includes a transitional surface  68 , which extends at a right angle to the center line  28 . In other words, the transitional surface is substantially vertically oriented. 
   Complementary to the transitional surface  68 , the sliding block  64  includes a flat surface  72  at its rear side. This flat surface  72  extends at a right angle to the direction of the center line  28 . When the flat surface  72  rests on the transitional surface  68 , as in the case of an open breech mechanism, as shown in  FIG. 6 , there is no transfer of any transverse force of the bolt head carrier  62  on the bolt head  44  or vice versa, because this force would act vertically to the surfaces  68 ,  72 . In this open breech state, the bolt head  44  does not tend to rotate, and therefore also does not stress the guide formations in the casing in transverse direction. Even when the interior of the casing becomes dirty, which can easily happen when a machine gun is held ready to fire over a longer period of time, there is little resistance on the closing breech mechanism. In particular, there is little friction in the guide formations (grooves and/or rails). Accordingly, the light weight machine gun  10  functions perfectly even when heavily soiled, and the wear and tear is kept as low as possible. 
   The sliding block  64  may be configured to have a second surface  74  that is parallel to and opposite the first surface  72 . If surface  72  is worn out, the sliding block  64 , as described in connection with  FIG. 5 , may be removed, turned 180° about its own longitudinal axis and reinserted. Now the new, not yet worn out surface  74  points to the rear and assumes the task of the worn out surface  72 . 
   Certain aspects of the operation of the light weight machine gun  10  are now described in conjunction with  FIGS. 6 and 7 . As shown in  FIG. 6 , the carrier  62  and the bolt head  44  are being forced toward the barrel  12  by a spring (not shown). As described above, the barrel  12  includes the extension  50  having the radial cam  52 . Accordingly, shortly before reaching the transverse plane at the rear end of the barrel  12  and right after running into the abutment  30 , the locking peg  48  (hidden in  FIG. 6 ) engages the radial cam  52  and the bolt head  44  is rotated counter-clockwise. As the bolt head  44  is locked into place, the sliding block  64  rotates counter-clockwise, thereby moving the flat surface  72  downward from the transitional surface  68 , causing the bolt head  44  to move rearward. In the locking process the locking pegs  46 ,  48  engage the first part  36  of the abutment  30 , and the bolt head  44  runs into the transverse plane of the barrel  12 . The middle and rear sections of the crank  66  act on the sliding block  64  in such a way that the bolt head  44  is exactly rotated to facilitate the engagement. The moment of the shot is shown in  FIG. 7 . 
   During the shot the bolt head carrier  62 , propelled by a gas piston, recoils from it position shown in  FIG. 7 , without first rotating the bolt head  44 . An example recoil mechanism is described in U.S. patent application Ser. No. 11/027,935, which is incorporated herein by reference. At this point, the locking pegs  46 ,  48  are engaged with the first part  36  of the abutment  30  and keep the bolt head  44  locked against the barrel  12 . As the bolt head carrier  62  moves rearward and the bolt head  44  is locked in place, the sliding block rotates clockwise from its position in  FIG. 7 , thereby rotating the bolt head  44  clockwise and disengaging the locking pegs  46 ,  48  from the first part  36  of the abutment  30  and allowing the breech mechanism  60  to move rearwardly. This returns the bolt head  44  back into the position of  FIG. 6 . 
   After the light weight machine gun  10  has been fired and the barrel  12  is hot, the hot barrel  12  is replaced with a cold barrel  12 . In the barrel replacement process, the extension  50  of the second part  38  of the abutment  30 , and hence the radial cam  52 , are also replaced. If the radial cam  50  of the hot barrel  12  is damaged or soiled, the barrel  12  can be scrapped or the radial cam  50  can be cleaned after it has cooled off. 
   If easily replaceable wearing parts are provided, they can be matched in hardness and material quality to the opposite surfaces in such a way that the opposite surfaces are not worn out or are worn out significantly less than the wearing surfaces. 
   One of ordinary skill in the art would appreciate the improvement the illustrated example makes over the prior art. In particular, the exchangeable barrel should be as economical as possible in light of all the causes of wear and tear. Also replacing the breech mechanism should be avoided. The prior art (e.g., EP-803 698) provides for a separation of the abutment, which simplifies the manufacture of the weapon. This is especially important in the usage of modern, small-caliber cartridges where the weapon components are considerably reduced in size and require greater finishing accuracy. When separating the abutment it is no longer necessary to use thin end mills to go through openings in the receptacle or in the casing to reach the reference surfaces of the abutment that are to be milled. Rather the reference surfaces are easily accessible, can be easily milled and polished, and have their measurements checked. Also, verification of the measurements is important because it makes the work of the weapons mechanic in the unit easier and more precise. 
   As discussed above, the front part of the abutment, which is associated with the barrel, bears great loads when the breech mechanism closes under the dynamic effect of the breech closing spring. Additionally, with machine guns, the breech mechanism is open in the ready-to-fire state until the trigger is pressed. Once the trigger is pressed, the breech mechanism closes, takes a cartridge from the magazine or belt, puts the cartridge into the cartridge chamber and fires it. As a result of the breech mechanism remaining in the rear and open position as long as there is a cartridge in the weapon and the weapon is not currently being fired, the machine gun is very easily and likely to become dirty. This dirt is pushed forward by the breech mechanism and can, under unfortunate circumstances reach the guide curve of the abutment, where it causes increased damage and wear. 
   One of ordinary skill in the art would appreciate that the illustrated example improves over the prior art with the use of a curved or cammed section  52  in the second part  38  of the abutment  30 , which controls the engagement of the breech mechanism in the abutment  30  when said breech mechanism closes. The greatest surface pressure takes place on this curved section  52 . Also, in accordance with the illustrated example, this curved section  52  is located on the barrel  12  and is distant from its rear side. If wear and tear takes place there, then the marksman can easily recognize scoring in the curved section  50  when changing the barrel  12  and then have the curved section  50  scrapped with the associated barrel  12 . 
   One of ordinary skill in the art would appreciate that the illustrated example can be used with breech mechanisms that have locking rollers. However, the illustrated example is particularly useful with a breech mechanism which has a straight-line movable bolt head carrier  62 , a rotating bolt head  44  located in the bolt head carrier  62  and a device for rotating the bolt head  44 . In such an arrangement, the bolt head  44  engages the first part  36  of the abutment  30  during rotation, and the bolt head  44  can be rotated by running into the second part  38  of the abutment  30  forming the curved section  50 . The abutment  30  of breech mechanisms with pivotally arranged bolt heads is difficult to manufacture, unless it is separated as described above. However, there is another advantage: the abutment  30  is relieved of all the work of rotating the bolt head  44  because the radial cam  52 , which forms the second part  38  of the abutment  30  and is associated with the barrel  12 , assumes that duty. 
   In the shown example of a machine gun with a rotating breech mechanism, a sliding block  64  is located laterally on the bolt head  44 , which engages in a crank  66  on the bolt head carrier  62 . As the breech mechanism closes and the bolt head  44  locks, the sliding block  64  lies on a transverse plane of the crank  66 , which extends at a right angle to the direction of motion of the breech mechanism  60 . Thus, the locking of the bolt head  44  in the abutment  30  is triggered exclusively by the second part  38  of the abutment  30  that has the curved section  52 . This greatly reduces wear on the breech mechanism  60 , because the crank  66  no longer has to provide for the locking. While it is difficult to close the breech mechanism noiselessly, with machine guns this is not a concern since the round is triggered with the closing of the breech mechanism. 
   One of ordinary skill in the art would appreciate that the illustrated example is improved by the fact that the sliding block  64  with a guide surface lies at random on the transverse plane of the crank  66 . This prevents concentrated load or strip load from occurring in the moment of the greatest load on the sliding block  64  and on the guide surface of the crank  66 . 
   It is further appreciable to one of ordinary skill in the art that the sliding block  64  can be attached in any way in the breech mechanism  64 . According to one example, it is inserted laterally into the bolt head  44  and then held by the firing pin. Accordingly, the firing pin facilitates the convenient and rapid interchangeability of the sliding block  64 , when it is worn out. 
   One of ordinary skill in the art would recognize the ease with which the surface  72  of the sliding block  64  can be replaced. The sliding block  64  has a second surface  74  opposite the surface  72 . When the surface  72  needs to be replaced, the firing pin is removed and the sliding block  64  is extracted from the bolt head  44 . The sliding block  64  is then rotated 180° and reinserted into the bolt head  44  so that the surface  74  is now in the position once occupied by the surface  72 . Basically, a sliding block  64  is created which in the case of wear and tear is easily removed, turned over and used again, namely on the part of its surface that had been unused up to then. 
   Although certain example methods and apparatus have been described herein, this patent covers all methods, apparatus and articles of manufacture fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents.