Patent Publication Number: US-6658983-B2

Title: Gun muffler and noise abatement system for large caliber gun

Description:
FIELD OF THE INVENTION 
     The present invention relates to a gun muffler and a system for minimizing the noise generated by the firing of a large caliber gun and, when desired, for stopping a projectile fired by the gun. 
     BACKGROUND OF THE INVENTION 
     Due to the increased population in the world, the noise generated by the testing of large caliber weapon systems in communities located near testing facilities of such weapon systems is becoming an increasing problem. As a result of this concern, there has been a need for a gun muffler or system for attenuating the generated noise level. Preferably, such a system should be able to rapidly and safely attenuate the noise generated by the firing of a projectile by a large caliber gun. 
     When a firing range has limited space, it is desirable to cause the projectile fired by a gun to be stopped a short distance from the firing of the gun. Accordingly, a system for attenuating the generated noise level should also preferably be capable of stopping a projectile fired by the gun. 
     U.S. Pat. No. 5,686,688, which is incorporated herein by reference, discloses a noise abatement system for a large caliber gun. The noise abatement system includes a gun muffler and a projectile stop, both of which are mounted on a concrete slab. The gun muffler may include a sabot catcher that is disposed within one of the pressure vessels for entrapping particulates caused by the firing of a gun. The catcher may be made of any suitable material for permitting gas to pass through but for preventing the passage of particulates. An example of the catcher is cables woven together as a sabot catcher. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a gun muffler and a noise abatement system for minimizing the noise generated by a firing of a large caliber gun having a gun tube. 
     The gun muffler includes a transition section fitted around the gun tube and engaging the gun tube for preventing the escape of residual combustion gases caused by the firing of a projectile by the gun. Attached to the transition section is at least one pressure vessel which defines a pressure vessel chamber for containing residual combustion gases and attenuating pressure waves. A catcher is disposed within the pressure vessel for entrapping particulates and for permitting the projectile to pass, and includes a plurality of columns adapted for being removably attached within the pressure vessel. 
     The noise abatement system includes a horizontal concrete slab and a gun muffler, as that described above, adapted for being mounted on the concrete slab. The noise abatement system may further include a projectile stop, mounted on the concrete slab and longitudinally aligned with the gun muffler, for stopping the projectile fired by the gun and for permitting the projectile to pass. As discussed above, a catcher is disposed within the pressure vessel for entrapping particulates and for permitting the projectile to pass, and includes a plurality of columns adapted for being removably attached within the pressure vessel. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is best understood from the following detailed description when read in connection with the accompanying drawings, in which: 
     FIG. 1 is a fragmentary longitudinal side elevational view of the left portion of a first embodiment of a gun muffler used with the present invention; 
     FIG. 1A is a fragmentary longitudinal side elevational view of the right portion of the gun muffler shown in FIG. 1; 
     FIG. 2 is an elevational view of the reinforced left-end plate of the gun muffler; 
     FIG. 3 is an elevational view of the reinforced right-end plate of the gun muffler; FIG. 4 is a fragmentary transverse vertical sectional view, showing the orifice plate, taken along the line  4 — 4  of FIG. 1A; 
     FIG. 5 is a fragmentary side elevational view of a gun and gun muffler, partly in section; 
     FIG. 6 is a fragmentary side elevational view of a gun, having a longer tube than the gun shown in FIG.  5  and the gun muffler, partly in section; 
     FIG. 7 is an enlarged fragmentary transverse sectional view, showing a tube transporter used with the present invention; 
     FIG. 8 is an enlarged fragmentary horizontal sectional view of a portion of the tube transporter of FIG. 7, taken along the line  8 — 8  of FIG. 7; 
     FIG. 9 is a fragmentary vertical sectional view of the tube transporter of FIG. 7, taken along the line  9 — 9  of FIG. 8; 
     FIG. 10 is a fragmentary longitudinal side elevational view of the right portion of a second embodiment of a gun muffler used with the present invention; 
     FIG. 10A is a fragmentary longitudinal side elevational view of the left portion of the gun muffler shown in FIG. 10; 
     FIG. 11 is an enlarged fragmentary sectional view of the first and second orifice plates shown in FIG. 10A; 
     FIG. 12 is an enlarged fragmentary sectional view of the third orifice plate shown in FIG. 10A; 
     FIG. 13 is a plan view of an orifice plate having a circular, off-centered orifice; 
     FIG. 14 is a plan view of an orifice plate having an elliptical orifice; 
     FIG. 15 is a longitudinal side elevational view of the noise abatement system of the present invention; 
     FIG. 16 is an enlarged transverse end view, showing an end of the enclosure of a gun muffler used with the present invention, taken along the line  16 — 16  of FIG. 15; 
     FIG. 17 is enlarged transverse view (with the end wall removed), showing an end of a gun muffler used with the present invention, taken along the line  17 — 17  of FIG. 15; 
     FIG. 18 is an enlarged transverse end view, showing the other end of the enclosure of a gun muffler used with the present invention, taken along the line  18 — 18  of FIG. 15; 
     FIG. 19 is an enlarged transverse sectional view, showing the connection between the projectile stop and the concrete slab, taken along the line  19 — 19  of FIG. 22; 
     FIG. 20 is an enlarged transverse end view, showing the end of the projectile stop closest to the gun muffler used with the present invention, taken along the line  20 — 20  of FIG. 15; 
     FIG. 21 is an enlarged transverse end view, showing the other end of the projectile stop, taken along the line  21 — 21  of FIG. 15; 
     FIG. 22 i side elevational view of the projectile stop shown in FIG. 15; 
     FIG. 23 is top plan view of the projectile stop shown in FIG. 15; 
     FIG. 24 is a fragmentary longitudinal side elevational view of the left portion of another embodiment of a gun muffler used with the present invention; 
     FIG. 24A is a fragmentary longitudinal side elevational view of the right portion of the gun muffler shown in FIG. 24; 
     FIG. 25 is a fragmentary top sectional view, showing an arrangement of a sabot catcher within the main pressure vessel of the gun muffler of FIG. 24, taken along the line  25 — 25  of FIG. 24A; and 
     FIG. 26 is a longitudinal side elevational view of another embodiment of a noise abatement system of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is directed to a gun muffler and a noise abatement system for a large caliber gun having a gun tube. As used herein, a “large caliber gun” refers to a gun having the size of at least 155 mm. Although a muffler used with the present invention could be made for smaller guns, for example, as low as 30 mm, it is normally not needed to muffle the noise generated from such smaller guns. With a gun muffler used with the present invention, the noise level is attenuated by 30% at 100 yards from the firing of the gun and by 95% at 300 yards from firing of the gun. 
     Referring to FIGS. 24-25, a gun muffler  350  in accordance with an embodiment of the present invention is shown. In addition to comprising a sabot catcher  385 , the gun muffler  350  can comprise some or all of the features from a gun muffler  50  discussed below in connection with FIGS. 1-9, a gun muffler  150  discussed below in connection with FIGS. 10-14, or a gun muffler  250  discussed below in connection with FIGS. 15-23. These systems are also described in U.S. Pat. No. 5,686,688, which is incorporated herein by reference. Alternatively, the gun muffler  350  can comprise a combination of features from the gun mufflers  50 ,  150 ,  250 . As an example of an embodiment and for simplicity reasons, FIGS. 24-25 show the gun muffler  350  comprising the sabot catcher  385  in relation to the gun muffler  50  discussed below in connection with FIGS. 1-9. The gun muffler  350  serves to attenuate pressure waves caused by a firing of a projectile of a gun, and the sabot catcher  385  is adapted for entrapping particulates and for permitting the projectile to pass through. 
     Referring to FIGS. 1 and 1A, the gun muffler  50  includes a transition section  4  which fits around the gun tube  24  and engages the gun tube for preventing the escape of residual combustion gases caused by a firing of the gun. At least one pressure vessel is attached to the transition section  4 . As shown in FIGS. 1 and 1A, the pressure vessels include a main pressure vessel  2  defining a main pressure chamber  32  and an extension pressure vessel  3  defining an extension pressure chamber  33 . Extension pressure vessel  3  is disposed in series with and connected to main pressure vessel  2 . The two pressure vessels  2 ,  3  may be bolted together. 
     As shown, the main pressure vessel  2  and the extension pressure vessel  3  are generally cylindrical. In one embodiment, the main pressure vessel  2  is about 4,000 cubic feet (9 feet in diameter and 64 feet long) and the extension pressure chamber  33  is approximately 1,000 cubic feet. 
     The main pressure vessel  2  includes a port  26 . A vent stack  20  is coupled to the main pressure vessel  2  at the port  26  and includes a lower vent stack  15  and an upper vent stack  16 . The lower vent stack  15  is in permanent fluid communication with the main pressure chamber  32  by way of the port  26 . Disposed in the upper vent stack  16  is an exhaust blower  17 . The exhaust blower  17  should be capable of rapidly creating a vacuum in the main pressure chamber  32  and the extension pressure chamber  33  for venting residual combustion gases from these chambers  32 ,  33  to the atmosphere by way of the port  26 . The blower  17  may be a squirrel-cage blower having drum type blowers or vanes. 
     Disposed in the vent stack  20  is a valve  18 , which separates the upper vent stack  16  from the lower vent stack  15 . Accordingly, the valve  18  is disposed between the main pressure chamber  32  and the exhaust blower  17 . The valve  18  is actuated by actuator  19 , which is air-operated. The valve  18  should be capable of withstanding high pressure, for example, pressure above 600 psi. 
     According to an embodiment of the invention, the valve  18  is a commercially available butterfly valve having a twenty-four inch diameter through the port  26  and is capable of operating at 1,000 psig. Also, the actuator  19  can be a pneumatic actuator which operates at 100 psig and is controlled by an electrically operated solenoid valve. The valve  18  is operated to be closed during firings of the gun and opened between firings of the gun. 
     At the end of the main pressure vessel  2  which is coupled to the extension pressure vessel  3  is an orifice plate  7 . The orifice plate  7  is an annular disk defining a central circular hole through which the projectile passes. The size of the hole is dictated by the size of the projectile. Also, if the hole is too small, it is difficult to rapidly vent the extension pressure chamber  33  through the hole and out through the port  26  by way of the exhaust blower  17 . On the other hand, if the hole of the orifice plate  7  is too large, the muffling of sound is not sufficient. It has been found that for a projectile of 155 mm, the orifice plate  7  should have a hole of about ten inches in diameter. 
     As shown in FIG. 1A, two baffle and orifice assemblies are disposed in series in the extension pressure chamber  33 . These energy-absorbing baffle and orifice assemblies each comprise a baffle  5  and an orifice plate  6 . Baffles  5  are generally conical in shape, having a diameter which linearly decreases from the entry end of the extension pressure chamber  3  to the exit end of the extension pressure chamber  3 . The baffle  5  abuts against the orifice plate  6 , which is also shown in FIG. 4. A retaining wall  28  is coupled to the extension pressure chamber  3 , and the orifice plate  6  is mounted to the retaining wall  28  by way of straps  21  and nuts and bolts  30 . Similar to the orifice plate  7 , the orifice plate  6  defines a central hole  27  through which a projectile passes. The diameter of the hole  27  is defined by similar functional requirements as the diameter of the hole of the orifice plate  7 . 
     Also shown in FIG.  1 A and are vent/access stacks  8 ,  9 ,  10 . The vent/access stacks  8 ,  9 ,  10  include stack covers  22 , which could be mounted by way of a hinge to the vent/access stacks. Each vent/access stack covers an access cover  23  which is mounted over an access port  25 ,  35 . The access ports  25  are in communication with the extension pressure chamber  33 , and the access port  35  is in communication with the main pressure chamber  32 . The purpose of these access stack assemblies is to permit personnel to enter into the main pressure chamber  32  or the extension pressure chamber  33  for maintenance or repair. 
     Because of the size and weight of the parts of the vent/access stacks  8 ,  9 ,  10  cranes  11 ,  12 , each having crane arms  14 , are used to remove and replace the stack covers  22  and the access covers  23 . Furthermore, crane  13 , having crane arm  14 , is used to remove and mount the transition section  4 . 
     FIGS. 2 and 3 show respectively the left-end plate  40  and right-end plate  41  of the present invention. Each end plate  40 ,  41  includes individual plates  42  which are connected to one another by connector beams  43 . Each end plate  40 ,  41  defines a central hole  44 . Preferably, each end plate  40 ,  41  includes removable annular disks  45  so that the diameter of the central hole  44  can be changed to accommodate various sizes of guns. 
     The left-end plate  40  is placed vertically at the entry end of the transition section  4 . A gun tube is pushed through the central hole  44  and into the transition section  4 . Preferably, the innermost removable annular disk  45  sealingly engages the gun tube. 
     The right-end plate  41  is placed on the exit end of the extension pressure chamber  3 . A supplemental tube is placed through the central hole  44 . Preferably, the innermost annular disk  45  sealingly engages the supplemental tube. 
     The purpose of the left-end plate  40  and the right-end plate  41  is to retain sand so that the main pressure vessel  2  and the extension pressure vessel  3  can be entirely covered in sand during operation. By covering the muffler  50  in sand, the muffling effect is increased, although the muffler need not be covered in sand. 
     FIGS. 5 and 6 show the transition section  4  in detailed cross section. FIG. 5 shows a gun having a shorter gun tube than the gun tube of FIG.  6 . In either case, the transition section  4  includes radially inward protruding flanges  52 ,  53  which serve as seals for engaging gun tube  24  for preventing residual combustion gases caused by the firing of the gun from escaping back through the transition section  4 . FIG. 6 also shows a supplemental tube  55  having an enlarged portion  57  which fits over the gun tube  24 . The projectile passes through the gun tube  24  and through the supplemental tube  55  through the entire muffler  50 . 
     FIG. 7 shows a cross section of the main pressure vessel  2  at a point through which the supplemental tube  55  extends. A supplemental tube transporter assembly  60  is shown. The supplemental tube transporter assembly  60  includes a first extendable arm  61   a  and a second extendable arm  61   b . At one end of each extendable arm is a coupling  63   a,b  respectively, for coupling each extendable arm to a respective pair of wheels  65   a,b . As shown in FIG. 8, the wheels  65   a,b  engage and move along respective tracks  67   a,b , which extend parallel to one another and longitudinally along the inner surface of the main pressure vessel  2 . Such a transporter tube assembly  60  could also be disposed in the extension pressure chamber  33 . The supplemental tube transporter assembly  60  also includes flanges  69   a,b  respectively coupled to the ends of the extendable arms  61   a,b  opposite the ends attached to the wheels. Flanges  69   a,b  are selectively attached to the supplemental tube  55 . 
     In operation,. the transporter tube assembly  60  is used to transport the supplemental tube  55  from the exit end of the extension pressure chamber  3  to a point so that it engages with a gun tube  24 . This is done by first rolling the wheels  65   a,b  along tracks  67   a,b  towards the exit end of the pressure vessel. Then, the supplemental tube  55  is pushed through the exit hole of the extension pressure vessel  3  and into the extension pressure chamber  33 . The extendable arms  61   a,b  are extended so that flanges  69   a,b  are in engagement with the supplemental tube  55 . Then, the entire assembly  60  is moved towards the entry end of the pressure vessel. 
     After placing the supplemental tube  55  in engagement with the gun tube and securing the transition section  4  over the top of the gun tube, the gun is ready for firing. Initially, the valve  18  is closed when the gun is fired. As a consequence of firing, combustion gases fill the main pressure chamber  32  and the extension pressure chamber  33 . The pressure waves caused by the filing of the gun are attenuated by the orifice plate  7  and the baffle and orifice plate assemblies disposed in series in the extension pressure chamber  33 . Thus, both pressure vessels  2 ,  3  serve to contain residual combustion gases and attenuate the pressure waves. 
     Immediately after firing and attenuation of the pressure waves, the valve  18  is opened thereby permitting the exhaust blower  17  to remove the residual combustion gases from the main pressure chamber  32 . This process is repeated rapidly. As mentioned above, the main pressure vessel  2  and the extension pressure vessel  3  are preferably covered with sand, which is contained by the left-end plate  40  and the right-end plate  41 . 
     The gun muffler  150  in accordance with another embodiment of the present invention is shown in FIGS. 10 and 10A. In the same manner as the gun muffler  50 , the gun muffler  150  includes a transition section  104  and at least one pressure vessel. Preferably, the gun muffler  150  includes a main pressure vessel  102  defining a main pressure chamber  132  and an extension pressure vessel  103 , disposed in series with and connected to main pressure vessel  102  and defining an extension pressure chamber  133 . The volume and shape of the pressure vessels  102 ,  103  may be similar to those of the pressure vessels  2 ,  3  of the gun muffler  50 . Also similar to the gun muffler  50 , the gun muffler  150  includes a vent stack  115  and an exhaust blower and valve assembly  120  connected to vent stack  115 . As in the gun muffler  50 , the valve of an exhaust blower and valve assembly  120 , which preferably is a butterfly valve, closes during firings of the gun for preventing pressure waves caused by firing from escaping directly to the atmosphere during firing and opens between firings for permitting said exhaust blower to remove residual combustion gases from said pressure chamber. The gun muffler  150  may also incorporate some other features from the gun muffler  50 . For example, the gun muffler  150  may include a tube transporter system shown in FIGS. 7-9. 
     The gun muffler  150  includes at least one orifice plate, which is adjustable relative to the pressure vessels and disposed in a pressure chamber, for attenuating pressure waves. More specifically, FIG. 10A shows three adjustable orifice plates. A first orifice plate  106   a  is disposed in the extension chamber  133  and has a first orifice, through which the projectile passes and which is adjustable relative to the longitudinal axis of the extension pressure vessel  103 . A second orifice plate  106   b  is disposed in series with the first orifice plate  106   a  in the extension pressure chamber  133  and has a second orifice, through which the projectile passes and which is adjustable relative to the longitudinal axis of the extension pressure vessel  103 . The first orifice plate  106   a  and second orifice plate  106   b  are identical. A third orifice plate  107  is disposed within the extension pressure chamber  133  near the connection of the main pressure vessel  102  to the extension pressure vessel  103  and has a third orifice, through which the projectile passes and which is adjustable relative to the longitudinal axis of the extension pressure vessel  103 . 
     The orifice plates may be made adjustable in any known manner. FIG. 11 shows one way to make the first and second orifice plates  106   a ,  106   b  adjustable. FIG. 11 shows either orifice plate and the surrounding elements and is discussed below with direct reference to the first orifice plate  106 a and parenthetical reference to the second orifice plate  106   b . A first (or second) mounting plate  151  is connected (i.e., welded or bolted) to the extension pressure vessel  103  and has a first (or third) bolt hole  153 . As shown in FIG. 10A, energy-absorbing baffles  105   a ,  105   b  may be respectively mounted to the first and second mounting plates  151   a ,  151   b . A first (or second) retaining ring  154  has a second (or fourth) bolt hole  155  aligned with first (or third) bolt hole  153  and has a first (or second) recess  156  confined by the first (or second) mounting plate  151 . The first (or second) orifice plate  106  is secured to the first (or second) mounting plate  151  and the first (or second) retaining ring  154  at the first (or second) recess  156 . 
     A first (or second) bolt  158  extends through the first bolt hole  153  and the second bolt hole  155  (or through third and fourth bolt holes). By loosening the first (or third) bolt  158 , the first (or second) orifice plate  106  may be adjusted to alter the location of a first (or second) orifice  159  relative to the longitudinal axis of the extension pressure vessel  103 . For example, the first (or second) orifice plate  106  may be rotated by rotating a first (or second) handle  160 , which is connected to the first (or second) orifice plate  106 . More than one handle may be used to rotate the orifice plate  106  for ease of rotation. Upon reaching a desired position of the first (or second) orifice  106 , the first (or third) bolt  158  is tightened to prevent further rotation of the first (or second) orifice plate  106 . 
     Similarly, as shown in FIG. 12, a third mounting plate  161  is connected (i.e., welded or bolted) to the main pressure vessel  102  and has a third:recess  166  and a fifth bolt hole  163 . A third retaining ring  164  has a sixth bolt hole  165  aligned with the fifth bolt hole  163  and. confines the third recess  166 . The third orifice plate  107  is secured to the third mounting plate  161  and the third retaining ring  164  at the third recess  166 . A third bolt  168  extends through the fifth bolt hole  163 .and the sixth bolt hole  165 . By loosening the third bolt  168 , the third orifice plate  107  may be adjusted to alter the location of the third orifice  169  relative to the longitudinal axis of the extension pressure vessel  103 . For example, the third orifice plate  107  may be rotated by rotating a third handle  170 , which is connected to the third orifice plate  107 . More than one handle may be used to rotate the orifice plate  107  for ease of rotation. Upon reaching a desired position of a third orifice, the third bolt  168  is tightened to prevent further rotation of the third orifice plate  107 . 
     A first type of orifice plate is shown in FIG.  13 . The orifice plate  174  as shown has an orifice  175  which is circular and disposed off-centered relative to the orifice plate  174 . Also shown in FIG. 13 is a retainer ring. An alternative type of orifice plate is shown in FIG.  14 . There, the orifice plate  178  as shown has an orifice  179  which is elliptical. The orifice plates are adjustable in order to accommodate varying trajectories. Also, the orifice plate  178  having an elliptical orifice  179  is particularly useful if a projectile undergoes a drop in trajectory as it travels along the gun muffler  150 . 
     As shown in FIG. 10A, a plurality of side ports  182  may be disposed along the sides of the pressure vessel. Side ports  182  may be used for a variety of purposes. For example, the side ports  182  may be used for access, viewing, photography and radar. The side ports  182  may be made of a transparent material if used for viewing. According to this embodiment of the invention, the gun muffler  150  is not covered with sand in operation. 
     As shown in FIG. 10A, a sabot catcher  185  is disposed within one of the pressure vessels or entrapping particulates caused by the firing of a gun. The catcher  185  may be made of any suitable material for permitting gas to pass through but for preventing the passage of particulates. For example, it is known to use cables woven together as a sabot catcher. The catcher  185  is mounted to the main pressure vessel  102 , such as by being welded or bolted thereto. The catcher  185  is preferably disposed in the main pressure chamber  132  near the connection of the main pressure vessel  102  to the extension pressure vessel  103 . 
     When the gun muffler  350  comprises some or most of the features from the gun muffler  150 , it is preferred that the gun muffler  350  does not also comprise the catcher  185 . 
     As shown in FIGS. 24A and 25 and in accordance with an embodiment of the present invention, the sabot catcher  385  comprises a plurality of columns  386  that are disposed within the pressure vessels  2 ,  3  for entrapping particulates, such as soft metallic or plastic fragments (also referred to as the sabot) that separates from the projectile after the projectile is fired from the gun, and for permitting the projectile to pass through. The entrapment of the sabot by the columns  386  minimizes, preferably substantially minimizes or eliminates, potential damage that would otherwise be caused to the vessels  2 ,  3  by the sabot making contact with the vessels  2 ,  3 . Thus, the longevity of the vessels  2 ,  3  can be extended. 
     The columns  386  may be positioned in various arrangements so as to be effective in minimizing the potential damage that can be caused to the vessels  2 ,  3 , while also permitting the projectile to pass through. Each column  386  preferably extends generally vertically, relative to a central axis of the main pressure vessel  2 . The columns  386  preferably define two sets of columns  386  formed on both sides of the central axis of the main pressure vessel  2 , and an opening  388  between the two sets of columns  386  for allowing the projectile to pass through. As best shown in FIG. 25, each set of columns  386  is formed on a corresponding side of the central axis of the main pressure vessel  2  and the columns  386  are generally parallel to one another. Each column  386  is preferably staggered relative to an adjacent column  386  with respect to the direction along the central axis of the main pressure vessel  2  so as to provide each set of columns  386  with sufficient strength for absorbing and withstanding the physical contacts that will be made by the sabot. Other arrangements may also provide each set of columns  386  with sufficient strength. 
     The columns  386  are preferably adapted for being removably attached in the main pressure chamber  32  near the connection of the main pressure vessel  2  to the extension pressure vessel  3 . The columns  386  can be mounted to the main pressure vessel  2 , such as by being welded or bolted thereto or by any other method or sealing device known in the art. For example, if the columns  386  are mounted to the main pressure vessel  2  by welding, the columns  386  that are damaged by the contacts with the sabot can simply and efficiently be removed by grinding off the welding and then removing the damaged columns  386  from the main pressure vessel  2 . As replacements, new or undamaged columns  386  can then be removably attached to the main pressure vessel  2  at preferably about the same positions. 
     Preferably, each column  386  is comprised of steel, is substantially cylindrical, is filled with a particulate material  390 , preferably concrete, and has a diameter of about 1 foot. 
     Several or all of the columns  386  can alternatively be attached or removably attached at other locations in the vessels  2 ,  3 . Preferably, little or no space exists between the columns  386  in the direction of travel of the sabot or particulates to maximize blockage of the sabot or particulates. Also, each column  386  may extend from other positions or angles relative to the central axis of the main pressure vessel  2 , may be comprised of other materials, such as other metals or hard plastic, may be of other shapes, and may be filled with other particulate materials, such as sand. 
     Referring to FIG. 26, the noise abatement system of the present invention includes a concrete slab  210  and a gun muffler  450  mounted to the concrete slab  210 . The gun muffler  450  serves to attenuate pressure waves caused by a firing of a projectile of a gun. In addition to comprising the sabot catcher  385  as that described above, in connection with FIGS. 24-25, the gun muffler  450  can comprise some or all of the features from a gun muffler  50  discussed below in connection with FIGS. 1-9, a gun muffler  150  discussed below in connection with FIGS. 10-14, a gun muffler  250  discussed below in connection with FIGS. 15-23, or a gun muffler  350  discussed below in connection with FIGS. 24-25. Alternatively, the gun muffler  450  can comprise a combination of features from the gun mufflers  50 ,  150 ,  250 ,  350 . 
     The gun muffler  250  has a first end  252  which is adapted to be coupled to the tube of a gun, as discussed in more detail below. The gun muffler  250  is mounted to the concrete slab  210  in any known manner. For example, the gun muffler  250  may be mounted to the concrete slab  210  by using bolts in a similar manner as discussed below in connection with the mounting of the projectile stop  200  with the concrete slab  210 . 
     The concrete slab  210  may be prepared from any conventional poured concrete. 
     The concrete slab  210  should have a thickness sufficient to support the gun muffler  250   25  and the projectile stop  200 , including when the projectile stop  200  is loaded with a particulate material such as sand. Preferably, the concrete slab  210  may have a thickness of 2 to 6 feet, and more preferably 4 feet. As shown in FIG. 15, the concrete slab  210  has a greater thickness near end  252  of the gun muffler  250  than the remainder of the concrete slab  210 . Not shown in FIG. 15 is the gradual decrease in  30  thickness of the concrete slab  210  occurring between the first and second shown portions of the gun muffler  250  near the end  252 . As shown in FIG. 15, the concrete slab  210  is preferably horizontal. Preferably, the concrete slab  210  is anchored to the ground or earth. For example, a plurality of support piles  212  may extend downward from the concrete slab  210  to bedrock. 
     Shown in FIG.  15  and more clearly in FIGS. 16-18 is a housing or arch (e.g., a “Quonset” arch) which serves to protect the gun muffler and the related instrumentation, such as the valves, hatches, and electrical instrumentation, from the environment. Arch  220  may be any suitable material, such as light weight corrugated steel, sheet metal, or plastic. As shown in FIGS. 16 and 18, the arch  220  is disposed over the gun muffler  250  and has end walls  222 ,  224  at each end with, respectively, doors  223 ,  225  for personnel to enter the interior of the arch and open  254  in end wall  224 , as shown in FIG. 17 also shows the end  252  of the gun muffler  250 . An opening  226  exists in the arch  220  for permitting the valve and blower assembly  228  to extend through and to the exterior of the arch  220 . 
     FIGS. 20-23 show the ends, sides, and top of the projectile stop  200 . As shown, the projectile stop  200  is substantially rectangular in shape. Each side, wall, and top of the projectile stop  200  can be made of steel, preferably about 4 inches thick. As shown in FIG. 20, the projectile stop  200  is comprised of a first side wall  201 , a second side wall  202  (identical to the first side wall  201 ), and a top plate  203 . In use, the side walls  201 ,  202  may be 10 feet high, and the top plate  203  may be 12 feet wide. FIG. 19 shows how the projectile stop  200  is mounted to the concrete slab  210 . More specifically, an “L-connector”, 205  is mounted to the base of the side walls  201 ,  202  and; then is subsequently affixed to the concrete slab  210  by a bolt  213 . The L connector  205  may be connected to the side wall  201  by a similar bolt (not shown). 
     FIG. 21 shows doors  204   a ,  204   b  which are respectively mounted by conventional heavy duty hinges  206  to the side walls  202 ,  201 , respectively. Accordingly, the doors  204   a ,  204   b  can swing open and closed as needed. To lock the doors in a closed position, latches  207  are aligned with recesses in the doors (not shown) and bolts are subsequently screwed through recesses  208  in the latches and into the recesses of the doors  204   a ,  204   b  to keep the doors closed. 
     FIG. 22 shows the side wall  202  mounted on the concrete slab  210 . As shown, the side wall  202  can actually be comprised of a plurality of panels  232   a ,  232   b ,  232   c ,  232   d . The panels  232   a - 232   d  can be connected to one another by connectors  233   a - 233   c.    
     FIG. 23 shows the top plate  203 . In the same manner as the side walls  201  or  202 , the top plate  203  can actually be comprised of a plurality of top panels  234   a - 234   e , which can be connected by connectors  235   a - 235   d . The top plate  203  is coupled to the side walls  201 ,  202  in any known manner, such as by being bolted thereto, and may be removable by a crane, for repairs. 
     As shown in FIG. 15, the projectile stop  200  is longitudinally spaced from the gun muffler  250 . In operation, when it is desired to aim at a target beyond the projectile stop  200 , the doors  204   a ,  204   b  are opened and interior space  209  is emptied by a front end loader through the open end of the projectile stop  200 . When it is desired to stop the projectile, the doors  204   a ,  204   b  are shut and locked into place by use of latches  207 . Subsequently, the interior space  209  is filled with a particulate material, such as sand, through the open end of the projectile stop  200 . Then the gun is fired and the projectile subsequently retrieved upon emptying of the interior space  209 . 
     It is desirable to build the projectile stop of a sufficient size such that over 1 million foot-pounds of energy can be absorbed. In one embodiment, which is 10 feet high, 12 feet deep, and 32 feet long, such a projectile stop can absorb over 40 million foot-pounds of energy when filled with sand. Thus, such a system can be used to stop 6.1 inch diameter projectiles. 
     Although illustrated and described herein with reference to certain specific embodiments, the claims of the present invention are nevertheless not intended to be limited to the details illustrated and described. Rather, the claims are meant to cover various common modifications without departing from the spirit of the invention.