Abstract:
Firearm barrel change apparatus for a firearm having a receiver and a barrel with a portion configured to slide into the receiver. The firearm barrel change apparatus also includes a barrel receiving nut having provisions for slidably receiving the inner portion of a firearm barrel and a barrel retention member. The barrel retention member has a portion thereof sized and shaped to cooperate with the barrel receiving nut to lock the firearm barrel to the receiver. A special handguard assembly is also provided that allows the barrel retention member to be used with the barrel receiving nut without removing the handguard assembly.

Description:
BACKGROUND OF THE INVENTION 
     Firearms with barrels that are removable without the need to use special barrel changing equipment such as a barrel wrench and a barrel vise have been in use for a number of years. Sporting firearms with this feature, such as take down firearms, have been popular since they allow a firearm to be broken down into two relatively small packages for transportation purposes and then be readily assembled by the shooter when it is desired to use the firearm. Unfortunately, this type of firearm requires that the receiver and the barrel of the firearm be designed with take down features and this increases the complexity of the firearm. Also, in many cases firearms with this take down feature are not as accurate as rigid firearms without this feature. 
     Systems that will permit the barrel to be changed have been used in the past for machine guns in an attempt to take care of the barrel heating problem caused by the rapid firing of cartridges in the machine gun barrel. When a cartridge is fired in a firearm barrel powder is burned and this produces heat that is partly transferred to the firearm barrel. With a non-automatic type firearm, sufficient time exists between shots that this heat is partially dissipated and hence heating of the firearm barrel is not a problem. However, with an automatic weapon there is insufficient time between shots for the heat to be dissipated and hence the amount of heat build up in the barrel can cause the barrel to become too hot for the proper functioning of the weapon. Such barrel changing systems for machine guns have required that the machine gun be specifically designed with this barrel change feature and that the receiver be designed for this feature. This of course increases the complexity of the firearm. Both this barrel change system and the previously mentioned take down system use the same configuration of barrels and associated equipment. 
     In many instances it is highly desirable to have a firearm that can readily utilize different types of barrels. This is particularly true of military type firearms since they can be used in different situations where a different type of barrel would be necessary or desirable. For instance, for accurate long range shooting a relatively long heavy barrel would be desirable and a short light weight barrel would be desirable for close range shooting in a confined area. Many barrels came with provisions for attaching additional equipment such as a wide variety of sights, grenade launchers, etc. and it is desirable to change barrels to mount barrels that already have particular types of equipment to the receivers rather:.than having to mount the equipment to the barrel. 
     While it is possible to make such barrel changes, it can not normally be done at the using unit level since special barrel changing equipment is necessary. In addition, in the case of the U.S. Military M-16 type weapon, barrel changes can damage the aluminum receiver of the firearm. Consequently, frequent barrel changes of the M-16 type weapons should be avoided. 
     Consequently, although there have been barrel change firearm systems in the past such as the take down firearms and the machine gun barrel change systems, these have not been useful in providing a barrel change system that readily permits one receiver that has no barrel change provisions to be used with a variety of different types of barrels and equipment attached to the barrels. 
     SUMMARY OF THE INVENTION 
     This invention relates to firearms with changeable barrels and more particularly to firearms with readily changeable barrels. 
     Accordingly, it is an object of the invention to provide firearm barrel change apparatus that increases the effectiveness of the firearm. 
     It is an object of the invention to provide firearm barrel change apparatus that permits the firearm to be used in a variety of roles. 
     It is an object of the invention to provide firearm barrel change apparatus that permits one firearm to be used with a variety of different types of barrels. 
     It is an object of the invention to provide firearm barrel change apparatus that permits one firearm to be used with a variety of different types of barrels and attached equipment. 
     It is an object of the invention to provide firearm barrel change apparatus that permits one firearm to be used with a variety of different types of barrels and attached equipment without removing the equipment from the barrel. 
     It is an object of the invention to provide firearm barrel change apparatus that requires no modification to the basic firearm. 
     It is an object of the invention to provide firearm barrel change apparatus that uses a standard receiver. 
     It is an object of the invention to provide firearm barrel change apparatus that uses standard barrels. 
     It is an object of the invention to provide firearm barrel change apparatus that can be used to retrofit standard firearms. 
     It is an object of the invention to provide firearm barrel change apparatus that is easy to use to retrofit standard firearms. 
     It is an object of the invention to provide firearm barrel change apparatus that avoids damaging the receiver. 
     It is an object of the invention to provide firearm barrel change apparatus that avoids possible damage to firearms with aluminum receivers. 
     It is an object of the invention to provide firearm barrel change apparatus that maintains the accuracy of the firearm when the barrel is changed. 
     It is an object of the invention to provide firearm barrel change apparatus that does not require the removal of the handguard in order to change the barrel. 
     It is an object of the invention to provide firearm barrel change apparatus that uses a handguard that allows access to remove the barrel from the receiver. 
     It is an object of the invention to provide firearm barrel change apparatus that uses a handguard that only touches the barrel at its breech end. 
     It is an object of the invention to provide firearm barrel change apparatus that permits barrels to be changed without special tools. 
     It is an object of the invention to provide firearm barrel change apparatus for military use that permits barrels to be readily changed at the local unit level. 
     It is an object of the invention to provide firearm barrel change apparatus that is easy to use by the person using the firearm. 
     It is an object of the invention to provide firearm barrel change apparatus that requires very little training to use. 
     It is an object of the invention to provide firearm barrel change apparatus that is simple in its operation. 
     It is an object of the invention to provide firearm barrel change apparatus that has few parts. 
     It is an object of the invention to provide firearm barrel change apparatus that can be manufactured with the use of altered existing parts. 
     It is an object of the invention to provide firearm barrel change apparatus that is particularly useful with firearms having aluminum receivers. 
     It is an object of the invention to provide firearm barrel change apparatus that is particularly useful with firearms in which the surfaces for the bolt locking lugs are not part of the receiver. 
     It is an object of the invention to provide firearm barrel change apparatus that is particularly useful for firearms that use firearm barrels where the surfaces for the bolt locking lugs are attached to or form part of the barrel structure. 
     It is an object of the invention to provide firearm barrel change apparatus that is particularly useful with the M16 type firearms. 
     These and other objects of the invention will become apparent from the following described firearm barrel change apparatus for a firearm having a receiver and a barrel with a portion configured to slide into the receiver. The firearm barrel change apparatus includes a barrel receiving nut having provisions for slidably receiving a barrel retention member and a barrel retention member having a portion thereof sized and shaped to cooperate with said barrel receiving nut to lock the barrel to the receiver. A special handguard assembly is also provided that allows the barrel retention member to be used with the barrel receiving nut without removing the handguard assembly. A handguard extension assembly is also provided that can be added to the handguard assembly when longer barrels are attached to the receiver. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be hereinafter more fully described with reference to the accompanying drawings in which: 
     FIG. 1 is a perspective view of the firearm barrel change apparatus invention installed on an M-16 type firearm with certain portions thereof broken away for clarity; 
     FIG. 2 is a side elevational view of the structure illustrated in FIG. 1; 
     FIG. 3 is a sectional view of the firearm barrel change apparatus invention illustrated in FIG. 2 taken in the direction of the line  3 — 3  thereof; and 
     FIG. 4 is a sectional view of the firearm barrel change apparatus invention illustrated in FIG. 2 taken in the direction of the line  4 — 4  thereof. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     FIGS. 1,  2  and  3  illustrate the firearm barrel change apparatus invention  10  and associated conventional barrel  12  located in the upper receiver  14  of a conventional M-16 type firearm  16 . It should be noted that for ease of illustration that certain portions of the M-16 type firearm  16  that are not necessary for a proper understanding of the invention have been omitted. As illustrated, the conventional M-16 type firearm  16  with its upper receiver  14  and its lower receiver  18  is entirely conventional and is not modified. The same is true with the barrel  12  including its conventional retention flange  20  that projects circumferentially outward from the rear or breech end  22  of the barrel  12  and the adjacently located conventional barrel extension  24 . The M-16 type firearm  16  also is illustrated with a conventional bolt carrier assembly  26 . The conventional barrel  12  is also connected to an an associated conventional gas system  36  including a conventional gas tube  38 . 
     The upper receiver  14  has the conventional cylindrical circular cross section projection  40  on its forward end and this projection  40  has a standard threaded outer surface  42  and a standard circular shaped cross section hole  44  that is sized and shaped to slidably accept the barrel extension  24  on the breech end  22  of the barrel  12 . Normally a conventional barrel nut (not shown) would be placed over the barrel  12  and pushed to the rear end  22  of the barrel  12  so that it pushed against the retention flange  20  and then it would be threaded onto the threaded outer surface  42  on the projection  40  to secure the barrel  12  to the upper receiver  14 . As indicated previously, unfortunately the conventional barrel nut requires expert knowledge and tools that are not readily available to enable the barrel  12  to be installed in the upper receiver  14 . 
     Consequently, this firearm barrel change apparatus invention  10  replaces the conventional barrel nut with a unique barrel receiving nut  46 . This barrel receiving nut  46  has a generally cylindrical shape with a circular cross section shaped hole  48  that has threads  50  on the portion that is is adapted to be located closest to the upper receiver  14  that are sized and shaped to match and engage with the threads on the threaded outer surface  42  of the projection  40  on the upper receiver  14 . 
     The outer portion  52  of the hole  48  in the barrel receiving nut  46  is unthreaded and is sized and shaped to receive the rear or breech end  22  of the barrel  12  including slidably receiving the barrel retention flange  20  which is normally pushed up against the end  54  of the projection  40  on the forward end of the upper receiver  14 . The barrel receiving nut  46  has upper and lower rectangular slots  56  and  58  in it that are oppositely located and are located to have the rearward surfaces  60  and  62  of the respective slots  56  and  58  be located so that they are on the same plane A as the front or outer surface  64  of the barrel retention flange  20  when the breech end  22  of the barrel  12  is firmly pushed into the hole  48  in the barrel receiving nut  46  so that the rear surface  66  of the retention flange  20  is pushed up against the end  54  of the projection  40  on the forward end of the upper receiver  14 . 
     In addition to the barrel receiving nut  46 , the firearm barrel change apparatus  10  includes a barrel retention member  68  that has an upper projection  70  and a lower projection  72  that are sized and shaped to slide into the respective upper and lower slots  56  and  58  in the barrel receiving nut  46 . When the upper and lower projections  70  and  72  are in place in the respective slots  56  and  58  in the barrel receiving nut  46 , the barrel  12  is securely connected to the upper receiver is since the projections  70  and  72  have portions that bear against the front or outer surface  64  of the barrel retention flange  20  and hence prevent forward movement of the barrel  12  with respect to the barrel receiving nut  46  that is in turn connected to the upper receiver  14 . 
     The firearm barrel change apparatus  10  also includes a handguard assembly that is designated generally by the number  74 . The handguard assembly  74  in turn comprises a main handguard assembly  76  and a handguard extension assembly  78 . The main handguard assembly  76  comprises a generally cylindrical shaped handguard bushing  80  that has a generally hollow circular cross section. The handguard bushing  80  has a centrally located threaded hole  82  that is sized and has threads that match threads  84  that are located on the outer surface of the barrel receiving nut  46  so that the handguard bushing  80  can be secured to the barrel receiving nut  46  by screwing it onto the barrel receiving nut  46 . The main handguard assembly  76  also comprises a hollow circular cross section handguard tube  86 . The handguard bushing  80  has a recessed cylindrical outer surface portion  88  that is sized and shaped to slide into the end portion  90  of the circular cross section hole  92  in the handguard tube  86 . The handguard bushing  80  also has an enlarged greater diameter end flange portion  94  located adjacent to the recessed outer surface portion  88  and this flange portion  94  closes the inner opening  96  of the circular cross section hole  92  of the handguard tube  86 . The handguard tube  86  is secured to the handguard bushing  80  by conventional means such as conventional screws represented by the screw  98  in FIG.  2 . 
     The handguard bushing  80  has an aperture  100  extending through it from its forward surface  102  to its rearward surface  104  that is sized and shaped to slidably receive the gas tube  38 . In this connection, the cross section of the aperture  100  for the gas tube  38  is oblong shaped as illustrated in FIG.  3  and this permits minor lateral deviations in the position of the gas tube  38  as the barrel  12  is being connected to the upper receiver  14 . 
     The handguard bushing  80  also has an elongated vertically oriented slot  106  in the bushing  80  that is located, sized and shaped to receive the barrel retention member  68  when the projections  70  and  72  are inserted into the slots  56  and  58  in the barrel receiving nut  46 . In this connection, it should be noted that there is an cut out portion  108  in the opposite wall of the bushing  80  that is sized and shaped to receive the outer end portion  110  of the lower projection  72  of the barrel retention member  68  and there is also a rectangular shaped aperture  112  in the opposite wall of the handguard bushing  80  that is sized and shaped to receive the outer end portion  114  of the upper projection  70  of the barrel retention member  68  so that the outer end portion  116  of the upper projection  70  extends outside of the handguard bushing  80  when the barrel retention member  68  is in its fully seated locking position as illustrated in FIG.  3 . 
     As best illustrated in FIGS. 2 and 3, since the portion  88  of the handguard bushing  80  is covered by the inner end portion  90  of the handguard tube  86 , the inner end portion  90  of the handguard tube  86  has an elongated vertically oriented slot  118  that is substantially identical in shape to the slot  106  and is located to coincide with the slot  106  in the handguard bushing  80 . In addition, as indicated in FIGS. 2 and 3, the inner end portion  90  of the handguard tube  86  has a rectangular shaped aperture  120  that is located and sized to coincide with the rectangular shaped aperture  112  in the wall of the handguard bushing  80 . These apertures  118  and  120  in the inner end portion of the handguard tube  86  allow the barrel retention member  68  to be inserted into the handguard bushing  80  and the barrel receiving nut  46  to secure the barrel  12  to the upper receiver  14 . 
     It will be appreciated that the handguard assembly  76  of the firearm barrel change apparatus  10  is the free floating type since the handguard assembly  76  does not touch the barrel at any point other than through the barrel receiving nut  46 . As a consequence, the M-16 type firearm  16  that uses this handguard assembly  76  should have better accuracy than the same M-16 type firearm with a conventional handguard assembly. In addition, the handguard tube  86  has an elongated slot  122  extending through its upper surface in the forward end  124  of the handguard tube  86 . This slot  122  permits access to a gas adjustment fitting  126 , if there is one connected to the gas tube  38 , so that the gas flow in the gas tube  38  can be regulated by the user without removing the main handguard assembly  76 . 
     Since barrels  12  come in several lengths depending upon the anticipated use for the barrel  12  and the associated M-16 type firearm  16 , the firearm barrel change apparatus invention  10  also has provisions for being used conveniently with different length barrels  12 . In this connection, the handguard extension assembly  78  is used when the M-16 type firearm  16  is to be used with a long barrel  12 . 
     The handguard extension assembly  78  comprises a handguard extension bushing  128  and an associated handguard extension tube  130 . The handguard extension bushing  128  has a hollow circular shaped cross section with inner and outer identical cylindrical lip portions  132  and  134  that are separated by a larger diameter thin circular shaped flange portion  136 . The inner lip portion  132  is sized and shaped to slide into the inside of the outer or forward end portion  124  of the handguard tube  86 . The handguard extension tube  130  is substantially the same shape as the previously described main handguard tube  86  and it has substantially the same cross section. However, the length L 2  of the handguard extension tube is substantially less than the length L 1  of the handguard tube  86 . It has been determined that L 2 =L 1 /B where 1.25≦B≦2.0 and in the preferred embodiment B is substantially equal to 1.5. As indicated in FIG. 2, the lengths L 1  and L 2  sould be sufficient to substantially cover the entire barrel  12  from the upper receiver  14  to the front sight assembly  133 . 
     Since the outer lip portion  134  of the handguard extension bushing  128  is identical to the inner lip portion  132  that is sized and shaped to slide into the inside of the outer end portion  124  of the handguard tube  86 , the outer lip portion  134  is sized and shaped to slide into the inside of the inner end portion  138  of the handguard extension tube  130  that has the same cross section as the handguard tube  86 . The inner end portion  138  of the handguard extension tube  130  is secured to the outer lip portion  134  of the handguard extension bushing  128  by conventional means such as by screws  140  (only one of which is shown in FIG. 2) that extend through the inner end portion  138  of the handguard extension tube  130  into the outer lip portion  134  of the handguard extension bushing  128 . The larger diameter flange portion  136  of the handguard extension bushing  128  has the same outside diameter as the outside diameter of the handguard tube  86  and the handguard extension tube  130 . When the handguard extension assembly  78  is in use, it is secured to the outer end portion  124  of the handguard tube  86  by conventional means such as by screws  142  (only one of which is shown in FIG. 2) that extend through the outer end portion  124  of the handguard tube  86  into the inner lip portion  132  of the handguard extension bushing  128 . 
     As illustrated in FIG. 1, in a manner similar to the previously described handguard tube  86 , the handguard extension tube  130  has an elongated slot  144  extending through its upper surface in the forward end  146  of the handguard extension tube  130 . This slot  144  permits the user of the firearm  16  to have access to a gas adjustment fitting  148 , if there is one connected to the gas tube  38 , so that the gas flow in the gas tube  38  can be regulated by the user without removing the handguard extension assembly  78 . 
     The firearm barrel change apparatus invention  10  is manufactured in the following manner. The firearm barrel change apparatus invention  10  is made from conventional materials using conventional machining techniques known in the firearms manufacturing industry. In order to keep the firearm barrel change apparatus invention  10  light in weight, a suitable grade of aircraft aluminum is used for its parts where possible. In this connection, the handguard tube  86  and the handguard extension tube  130  are manufactured from aircraft grade aluminum tubing using conventional techniques known in the art. The handguard bushing  80  is manufactured by conventional machining techniques known in the art from suitable aircraft grade aluminum stock as is the handguard extension bushing  128 . The barrel receiving nut  46  and the barrel retention member  68  are manufactured using conventional techniques known in the art from a suitable grade of steel such as  4140  chrome moly for strength. The assembly of the components of the firearm barrel change apparatus invention  10  is conventional and is obvious to those skilled in the art. 
     The firearm barrel change apparatus invention  10  is used in the following manner. The firearm barrel change apparatus invention  10  can be used as part of an originally manufactured M-16 type firearm  16  or it can be used to retrofit an M-16 type firearm  16  that has a standard system of attaching the barrel  12  to the upper receiver  14 . In either situation the user of the M-16 type firearm  16  operates and fires the firearm in a conventional manner as it was used prior to the installation of the firearm barrel change apparatus  10 . However, with the firearm barrel change apparatus  10 , due to the free floating handguard assembly  74 , the firearm will usually shoot more accurately. 
     If the firearm barrel change apparatus  10  is added to the M-16 type firearm  16  at the time of the original manufacture of the firearm  10 , the conventional barrel nut (not shown) is not installed. In its place the barrel receiving nut  46  is installed on the existing threaded outer surface  42  on the projection  40  on the upper receiver  14 . To accomplish this a wrench of the type known in the art is used by inserting projections on the wrench into two installation slots  150  (only one of which is shown in FIG. 1) that are located opposite each other in the outer end of the barrel receiving nut  46 . The wrench is then turned to turn the barrel receiving nut  46  to install it on the projection  40  on the upper receiver  14 . 
     If the M-16 type firearm  16  is retrofitted with the firearm barrel change apparatus  10 , the standard conventional barrel nut is removed after removing the standard handguards, etc. and the firearm barrel  12  is also removed. The barrel receiving nut  46  is then installed by threading it onto the outer threaded surface  42  on the projection  40  of the upper receiver  14  using the previously described wrench and the slots  150  in the barrel receiving nut  46 . Then to install the firearm barrel  12  of the desired configuration and length, the handguard assembly  74  is connected to the barrel receiving nut  46  by threading the handguard bushing  80  onto the threads on the outer surface of the barrel receiving nut  46  making sure that the aperture  100  in the handguard bushing  80  is aligned with the corresponding hole for the gas tube  38  in the upper receiver  14 . 
     Then the breach end of the barrel  12  of the desired configuration and length is inserted into the receiving nut  46  and at the same time the end of the gas tube  38  is inserted into the aperture  100  in the handguard bushing  80  and into the upper receiver  14 . When the barrel  12  and the associated gas tube  38  are properly seated, the barrel retention member  68  is inserted into the slot  118  in the handguard tube  86  and the adjacent slot  106  in the handguard bushing  80  with the upper projection  70  and the lower projection  72  going into the slots  118  and  106  so that the upper projection  70  enters the rectangular shaped aperture  112  in the opposite wall of the handguard bushing  80  and the adjacent rectangular shaped aperture  120  in the wall of the handguard tube  86 . At the same time, the lower projection  72  is positioned so that its outer end portion  110  enters the cut out portion  108  in the opposite wall of the handguard bushing  80 . With the barrel retention member  68  in this position, the barrel  12  is securely connected to the upper receiver  14  of the M-16 type firearm since the projections  70  and  72  have portions that bear against the outer surface of the barrel retention flange  20  and portions that are located in the slots  56  and  58  of the barrel receiving nut  46  that is secured to the upper receiver  14 . Then the M-16 type firearm with the newly installed barrel  12  and associated handguard assembly  74  is used in a conventional manner. 
     When it is desired to change the barrel  12 , pressure is applied to the outer end portion  114  of the upper projection  70  of the barrel retention member  68  toward the barrel  12  by tapping with a blunt instrument or the like. This will cause the barrel retention member  68  to be forced out of the elongated slots  106  and  118  in the handguard bushing  80  and tube  86  and the free the barrel  12  from the upper receiver  14 . Then when another barrel  12  is to be connected to the upper receiver  14 , the process set forth above is repeated. If the barrel  12  is long, then the handguard extension assembly  78  is connected to the main handguard assembly  76  in the previously indicated manner prior to inserting the barrel  12  into the barrel receiving nut  46 . 
     As used herein the designation M-16 type of firearm includes but is not limited to the M-16, M-16A1, M-16A-2, M-16A-3, M-4, C7, C8, AR-15, AR-10, AR-10A1 and similar type firearms with various military and commercial designations. 
     Although the invention has been described in considerable detail with reference to certain preferred embodiments, it will be understood that variations or modifications may be made within the spirit and scope of the invention as defined in the appended claims.