Abstract:
The disclosed device is based on the Thompson submachine gun. The disclosed device is specifically designed to only fire blanks, or a firearm cartridge that contains gunpowder but no bullet, shot, or projectile. Blanks can be fired in fully automatic fashion, just as a standard machine gun. Numerous features are disclosed that prevent the disclosed device from being modified to fire live cartridges. The result is a blank-firing device with the appearance of a genuine firearm, while being unable to fire live cartridges, and thus not regulated by state or federal laws, or regulations to possess, use, and/or transfer.

Description:
FIELD 
     This invention relates to the field of replica firearms and more particularly to a device with the appearance of a firearm, but that only fires blanks and cannot be modified to fire live cartridges. 
     BACKGROUND 
     Battle re-enactors, movie and theatrical productions, law enforcement and military training, all require the use of machine guns to provide an accurate appearance and sound signature. To ensure safety, the machineguns used must be completely safe and unable to fire “live” ammunition. In addition to being safe, the guns must be strong enough to withstand the inevitable rough handling. In particular, during battle reenactments and training of police officers and soldiers, where the guns do not receive the careful handling present on a movie set. 
     Until now only two options have met this need—using real machine guns that are modified to shoot blanks, or using a gun that is too fragile for “live” ammunition. As a note, within the application the term “blanks” will refer to cartridges that make noise but do not contain a projectile. 
     Regarding the first option, or the use of real machine guns: in nearly every situation this option is cost-prohibitive. The regulations that control ownership of machine guns have limited the supply of machine guns, causing the remaining machine guns to be very expensive. 
     The registration of truly original machine guns was banned in 1968. The registration of post-1968 machine guns (i.e., copies of original machine guns) was banned in 1986. No one has been able to make a firing copy of any machine gun for thirty years. And in more than thirteen states the ownership of machine guns is completely banned. 
     Thus, the use of genuine guns is only an option for well-funded movies. 
     The second option, or the use of a fragile gun, is undesirable because the resulting gun cannot stand up to the rigors of battle reenactments or police training. 
     What is needed is a blank-firing device that behaves as a machine gun, but cannot fire live cartridges and cannot be modified to fire live cartridges. Moreover, the blank-firing device must look, feel, and act authentic. 
     SUMMARY 
     The disclosed blank-firing device is based on the Thompson submachine gun. The disclosed device can only fire blanks, or a firearm cartridge that contains gunpowder but does not contain a bullet, shot, or other such projectile. The device can fire the blanks in fully automatic fashion, feeding from the magazine with spent cartridges being ejected from the breech just as in the original Thompson machine gun. 
     The disclosed device is highly authentic and indistinguishable, both in appearance and function, from an original Thompson submachine gun. The disclosed device is designed and manufactured in identical fashion to the original, using machined parts that are as strong and sturdy as the original gun. However, the gun has unique design enhancements that render the gun incapable of modification to fire “live” ammunition. 
     While the preferred embodiment has the appearance of a Thompson machine gun, alternative embodiments of the device can take the appearance of other firearms. For example, an MP 40, a submachine gun used by Germany during World War II. 
     Disclosed within are numerous features that prevent the disclosed device from being modified to fire live cartridges. The result is a blank-firing device that cannot fire live cartridges, and thus does not require a machine gun tax stamp or other governmental registration to possess and use. 
     The main portions of the blank-firing device are based on a Thompson submachine gun. The disclosed parts are generally as follows: The receiver of the disclosed device connects to the barrel, forming the upper section of the device. A bolt slides within the bolt pocket of the receiver, the bolt charged by a recoil spring. Prior to initial firing, the bolt is drawn back using the cocking handle, which is accessible through a slot in either the side or top of the receiver. 
     The trigger assembly catches and releases the bolt depending on the position of the trigger. When released, the bolt travels forward, feeds a cartridge into the chamber, allows the firing pin to contact the cartridge, thus triggering combustion of the enclosed gunpowder. The combustion gas then exits through the barrel. This process allows the blank-firing device to behave exactly like the original in all aspects but for the firing of a projectile. 
     While the blank-firing device is modeled on the Thompson submachine gun, numerous features exist to prevent the use of parts from a Thompson submachine gun. Additional features exist to prevent the activation or discharge of any live cartridge that is inadvertently loaded into the device. 
     Given that it is the motion of the bolt that causes the cartridge to discharge, discussion of the safety features will begin there. 
     The bolt is comprised of a body and a head. At the end of the head is depression that the cartridge is held within, with a pin to activate the primer. 
     In the preferred embodiment, the disclosed device uses a depression of diameter less than that of any commercially available cartridge containing a projectile. The chosen depression fits only specially designed proprietary blank cartridges. A standard Thompson submachine gun uses a .45 ACP (11.43×23 mm) (Automatic Colt Pistol) cartridge. The .45 ACP has a rim diameter, or measurement at its base, of 12.2 mm or 0.48 inches. As a result of the undersized depression, the .45 ACP cartridge does not fit within the depression of the disclosed bolt head. 
     As an additional safeguard, the blank-firing device may be configured to use a rimfire primed cartridge, rather than a centerfire cartridge. Given that a 0.27 rimfire firing pin will not activate a centerfire cartridge, or a 0.22 rimfire cartridge, this provides an additional safeguard against the use of standard cartridges. 
     In theory, the undersized bolt could be removed and replaced with a bolt from a typical Thompson submachine gun. But many changes have been made to the device to make such a bolt substitution impossible. 
     First, the bolt pocket within the receiver has non-standard dimensions. In particular, the front wall of the bolt pocket is thicker than that of a standard Thompson. If a standard bolt is installed within the pocket, the firing pin of the bolt is unable to reach the cartridge, and thus the primer of the cartridge cannot be activated. 
     The bolt of the disclosed device has a longer head that compensates for this increased wall thickness. 
     However, a standard bolt cannot fit within the disclosed receiver because of the narrower bolt pocket. 
     These dimensional changes to the bolt pocket of receiver are a result of increases in receiver wall thickness. It is plausible that a user may seek to enlarge the bolt pocket to fit a standard bolt, thus allowing live cartridges to be used. But such alteration is prevented by multiple anti-machining pins. Anti-machining pins are a tamper proofing structure that prohibits the bolt pocket from being machined to a different size. 
     The anti-machining pins are embedded within pockets, or areas of missing material, within various parts of the blank-firing device. For example, within the walls of the receiver around the bolt pocket. 
     The disclosed anti-machining pins are hardened steel dowels with a circular cross-section. The hardness of a preferred anti-machining pin is measured as C52-62 on the Rockwell Hardness Scale. With such a high hardness, the anti-machining pins cannot be cut using high-speed steel or tungsten carbide cutting tools. Only destructive methods can remove the pins. 
     Given that the dimensions of the bolt pocket cannot be modified without first removing the anti-machining pins, and the pins can only be removed destructively, the receiver cannot be modified to accommodate parts from other firearms. It is tamper proof. 
     The bolt itself is manually drawn back using the cocking handle. The cocking handle protrudes from the bolt, through a slot in the receiver. To further render the disclosed device inoperable with standard Thompson parts, the slot for the cocking handle is offset from its typical position. Specifically, the cocking handle slot is offset 0.100 inch rearward and 0.05″ upward as compared to the standard location. 
     Thus, if a user could insert a standard bolt, the user could not fit a cocking handle to draw the bolt back to cock the device, and thus could not put the device in a position in which it could fire. 
     The bolt further includes two optional cavities that are filled with lead or lead shot, then closed using set screws. These cavities allow the weight of the bolt to be increased, thereby reducing the velocity of the bolt. Without a velocity reduction the cases of the fired cartridges are violently ejected, creating a potential hazard. 
     The disclosed changes prevent the use of any bolt other than the bolt intended for use in the disclosed device. These changes are sufficient to prevent the use of any ammunition other than the intended blanks. 
     Nonetheless, additional features are disclosed that further prevent the use of the disclosed device to fire live cartridges. 
     During assembly the barrel and receiver of the disclosed device are threaded together. This threaded connection is 7/8-16 UN thread type, whereas the standard Thompson thread is a square thread. Thus, the receivers and barrels of the disclosed device are non-interchangeable with those of a standard Thompson. Following threading, the barrel and receiver are optionally welded or brazed together, preventing the user from disassembling the parts. 
     With the barrel and receiver as a single piece, a user may attempt to cut the barrel from the receiver. But such cutting is prevented by additional tungsten carbide anti-machining pins. These anti-machining pins that are hidden within the barrel and receiver on either side of the connection. Thus, as above with the receiver pocket, any cutting must be destructive, and thus the resulting parts could not be used to create a functioning firearm. 
     The barrel of the disclosed device has additional safety features. In contrast to the barrel of a standard machine gun, the barrel of the disclosed device includes an obstruction that prevents the passage of any projectile. The obstruction of the preferred embodiment is a web-shape with three legs or sides. 
     The obstruction passes through substantially the entire length of the barrel. By making the obstruction substantially as long as the barrel, a user cannot cut off part of the barrel to remove the obstruction. Furthermore, by blocking the barrel along nearly its entire length, foreign objects cannot be inadvertently inserted into the barrel and later discharged when the blank cartridge releases its gas. 
     In alternative embodiments, the obstruction is located at the base of the barrel. In such embodiments, the user must again cut off all the barrel to remove the obstruction because cutting off only the end will leave the obstruction in place. 
     The web-shaped obstruction has no effect on the operation of the device. This is because firing blanks causes only the discharge of gas. The web-shaped obstruction blocks the passage of projectiles, but the cross-sectional area of the barrel is largely unblocked. 
     The disclosed device further includes a blank adapter. The blank adapter threads into the muzzle end of the barrel. The center of the blank adapter is open, to allow gas to pass through. But the center of the blank adapter has a smaller cross-sectional area than the remainder of the barrel. This reduced cross-sectional area restricts the flow of gas out of the barrel, creating backpressure. The backpressure provides the energy to cycle the bolt and operate the device. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention can be best understood by those having ordinary skill in the art by reference to the following detailed description when considered in conjunction with the accompanying drawings in which: 
         FIG. 1  illustrates a left-side view of the first embodiment. 
         FIG. 2  illustrates a right-side view of the first embodiment. 
         FIG. 3  illustrates an isometric view of the first embodiment with the upper half of the device separated from the lower half. 
         FIG. 4  illustrates a view of the upper half of the first embodiment. 
         FIG. 5  illustrates an isometric view of a receiver of the first embodiment. 
         FIG. 6  illustrates a side view of the receiver of the first embodiment. 
         FIG. 7  illustrates a bottom view of the receiver of the first embodiment. 
         FIG. 8  illustrates a bottom view of the receiver of the first embodiment with the bolt in its rear position. 
         FIG. 9  illustrates a bottom view of the receiver of the first embodiment with the bolt in its front position. 
         FIG. 10  illustrates a front view of a bolt of the first embodiment. 
         FIG. 11  illustrates a side view of the bolt of the first embodiment. 
         FIG. 12  illustrates a rear view of the bolt of the first embodiment. 
         FIG. 13  illustrates an isometric view of the bolt of the first embodiment. 
         FIG. 14  illustrates a front view of a barrel of the first embodiment. 
         FIG. 15  illustrates an isometric view of the barrel of the first embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to the presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. Throughout the following detailed description, the same reference numerals refer to the same elements in all figures. 
     Referring to  FIGS. 1 and 2 , left-side and right-side views of the first embodiment are shown, 
     The anti-tamper blank-firing device  1  consists generally of a receiver  30  coupled to a trigger housing  12 , grip  11 , butt stock  10 , barrel  100 , and magazine  16 . 
     Trigger housing  12  includes a trigger  14 , selective fire switch  24  to toggle between single shot mode and fully automatic mode, and gun safety switch  20 . In this embodiment, the cocking handle  80  protrudes through the top of the receiver  30 , but in other embodiments the cocking handle  80  protrudes from the left or right side of the receiver  30 . 
     The end of the barrel  100  is referred to as the muzzle  18 . The foregrip  15  covers the grip mount  90 . 
     Referring to  FIG. 3 , an isometric view of the first embodiment is shown with the upper half of the device separated from the lower half. 
     The anti-tamper blank-firing device  1  readily separates along a horizontal plane between the trigger housing  12  and receiver  30 . The bolt  50  is visible inside the receiver  30 . The foregrip  15  is hidden, rendering the grip mount  90  visible. 
     Referring to  FIG. 4 , a view of the upper half of the first embodiment is shown. The upper half of the anti-tamper blank-firing device  1  is the focus of the features that render the device inoperable with live cartridges, and thus it will be the focus of the discussion below. 
     The receiver  30  is shown with cocking handle slot  42 . The internal barrel web  112  is partially shown within the bore  114  of barrel  100 , and is discussed further below. 
     Referring to  FIG. 5 , an isometric view of a receiver of the first embodiment is shown. The first of the anti-tamper features is shown, with the anti-machining pins  120  shown. When complete, the anti-machining pins  120  lie within the anti-machining pin pockets  122 . But for purposes of illustration several the anti-machining pins are shown protruding beyond the receiver  30 . 
     Once installed, the anti-machining pins  120  block any attempts to cut the receiver  30  at the receiver barrel-engaging threads  44 . Thus, the receiver  30  cannot be cut to remove the barrel  100  with its projective blocking internal barrel web  112 . 
     Referring to  FIG. 6 , a side view of the receiver of the first embodiment is shown. 
     The anti-machining pins  120  are again shown, with one pin protruding from its corresponding anti-machining pin pocket  122  and the other fully installed within its anti-machining pin pocket  122 . 
     The cocking handle slot  42  is again shown. As discussed above, the cocking handle slot is offset rearward and upward as compared to the standard location, rendering the use of a standard bolt and cocking handle impossible. 
     Referring to  FIG. 7 , a bottom view of the receiver of the first embodiment is shown. 
     Receiver  30  includes a bolt pocket  32  inside of which the bolt  50  (not shown) may slide fore and aft. The forward limit of the motion of the bolt is set by the bolt pocket front wall  34 , which has a bolt pocket front wall thickness  35 . In the preferred embodiment, the bolt pocket front wall thickness  35  is ⅛″ greater than that of a standard Thompson. Thus, a standard bolt cannot slide far enough forward to activate the primer of a cartridge, and thus cannot fire a bullet. 
     The distance between the bolt pocket front wall  34  and bolt pocket rear wall  37  defines the bolt pocket length  38 . 
     The bolt pocket side walls  36  define a bolt pocket width  40 . In the preferred embodiment, the bolt pocket width  40  is 1/16″ narrower than that of a standard Thompson. Because of this decreased width, a standard bolt cannot be placed within the bolt pocket  32 . 
     Within the bolt pocket side walls  36  is a multiplicity of anti-machining pins  120  installed inside anti-machining pin pockets  122 . The anti-machining pins  120  are located to prevent an increase to the bolt pocket width  40  or a decrease of the bolt pocket front wall thickness  35 . Thus, the bolt pocket  32  cannot be modified to fit a standard Thomson bolt. 
     Referring to  FIG. 8 , a bottom view of the receiver of the first embodiment with the bolt in its rear position is shown. 
     The bolt  50  is shown in its rearmost position, near the bolt pocket rear wall  37 . Bolt  50  includes bolt head  52  and bolt body  54 . The bolt  50  does not rest against directly against the rear wall  37  because a spring retaining clip is installed between the two parts, but this part is not shown. 
     Referring to  FIG. 9 , a bottom view of the receiver of the first embodiment with the bolt in its front position is shown. 
     In this position the bolt  50  is resting against the bolt pocket front wall  34 . Given that the bolt pocket front wall thickness  35  is greater than that of a standard Thompson receiver, the bolt head of a standard Thompson will not reach far enough forward to activate a live cartridge. But the anti-tamper blank-firing device  1  uses a bolt head  52  that is ⅛-inch longer than a standard bolt head, thus compensating for the ⅛-inch increase in the thickness of the bolt pocket front wall  34 . As a result of the increased length, the disclosed bolt  50  has a head  52  that reaches far enough to activate a blank cartridge. 
     Referring to  FIG. 10 , a front view of a bolt of the first embodiment is shown. 
     The bolt head depression  53  is shown with two firing pins for purposes of illustration. A bolt head  52  of the device will only include one firing pin, the firing pin chosen to fit the desired ammunition. 
     The centerfire pin  68  is the more common firing pin. it is in the center of the bolt head depression  53 , designed to activate the primer in the center of the cartridge. The alternative is the rimfire pin  73 . The rimfire pin  73  is offset, intend to crush the rim of the 0.27 caliber primer. 
     The bolt head depression  53  is optionally undersized to fit only a purpose-built cartridge, thus preventing accidental firing of the .45 ACP cartridge generally used with a Thompson submachine gun. 
     Referring to  FIG. 11 , a side view of the bolt of the first embodiment is shown. The bolt  50  is shown with bolt head  52  and bolt body  54 . The bolt body  54  has the shape of a cuboid, or rectangular box. A single cavity  62  is shown, intended to hold lead shot to increase the weight of the bolt  50 . 
     Referring to  FIG. 12 , a rear view of the bolt of the first embodiment is shown. An optional bolt center cavity  55  is shown, intended to hold the recoil spring. Retention screws  66  are shown, designed to hold the lead shot within the cavities  62  of the bolt  50 . 
     Referring to  FIG. 13 , an isometric view of the bolt of the first embodiment is shown. The bolt  50  is shown with bolt head  52  and bolt body  54 . 
     Referring to  FIG. 14 , a front view of a barrel of the first embodiment is shown. The barrel  100  is shown with its internal barrel web  112 . The internal barrel web  112  is manufactured from the same, or similar, material as the barrel  100  itself. The internal barrel web  112  blocks any projectile from passing from the receiver into the barrel  100 . The internal barrel web  112  preferably extends the length of the barrel  100 , thereby preventing a user from removing the feature by cutting the barrel  100 . 
     In the preferred embodiment the internal barrel web  112  is machined from the same stock as the barrel  100 . 
     The barrel web  112  is shown with triangular holes, but other hole types may also be used. For example, circular holes. 
     Referring to  FIG. 15 , an isometric view of the barrel of the first embodiment is shown. 
     The barrel  100  engages with the receiver  30  at the barrel receiver-engagement threads  102 . To prevent a user from cutting the barrel  100  from the receiver  30 , and thereby removing the internal barrel web  112 , there are barrel anti-machining pins  106 . The barrel anti-machining pins  106  are slid through the barrel pin cavity channels  110  to rest within the barrel pin cavities  108 . When installed the pins  106  rest fully within the cavities  108  to avoid interference with the barrel receiver-engagement threads  102 . 
     Equivalent elements can be substituted for the ones set forth above such that they perform in substantially the same manner in substantially the same way for achieving substantially the same result. 
     It is believed that the system and method as described and many of its attendant advantages will be understood by the foregoing description. It is also believed that it will be apparent that various changes may be made in the form, construction, and arrangement of the components thereof without departing from the scope and spirit of the invention or without sacrificing all its material advantages. The form herein before described being merely exemplary and explanatory embodiment thereof. It is the intention of the following claims to encompass and include such changes.