US2530834A - Electrically fired perforating gun - Google Patents

Description

Nov. 2l, 1950 P. w. MARTIN ELECTRICALLY FIRED PERFORATING GUN 2 Sheets-Sheet l Filed Oct. 19, 1945 INVENTOR. PHILIP W. MARTIN ATTORNEY Nov. 2l, 1950 P. w. MARTIN 2,530,834

ELECTRICALLY FIRED PERFORATING GUN Filed OCI.. 19, 1945 2 Sheets-Sheet 2 PRESSURE INVENTOR. PHILIP W. MARTIN ATTORNEY Patented Nov. 21, 1950 ELECTRICALLY FIRED PERFORATING GUN Philip W. Martin, Huntington Park, Calif., a'ssignor to McCullough Tool Company, Vernon, Calif., a corporation of Nevada Application 0ctober 19, 1945, Serial No. 623,301

22 Claims.

This invention relates to perforating guns such as used in wells for perforating casing, and relates in particular to means in guns of this and other types for obtaining higher projectile velocities.

Owing to the small space in which well perforating guns are employed, the gun barrels are necessarily quite short. Therefore, the propelling effect of the expanding gases from the burning of the powder charge in these guns is limited to that short space of time which it takes for the projectile to travel through the barrel. For the purpose of obtaining a greater utilization of the potential projectile-propelling capacity of the powder charge employed in these guns, many expedients have been adopted, among which are shear rings on the projectiles and plates or flanges at the rear ends of the projectiles, to restrain the projectiles from movement until the pressure of combustion products from the burning of the powder against the rear ends of the projectiles builds up to an e-ective value. These expedients have accomplished higher projectile velocities and therefore greater penetrating ability of the projectiles but from tests and observations I have deterrnined that an efficient use of the powder is not obtained in these guns and that too large a portion of the powder is expelled from the gun barrels in unburned state and therefore without useful effect.

It is an object of my present invention to greatly increase the projectile-propelling eiliciency of the powder charge in perforating guns, as compared to that which is obtained in the most efficient guns of this character now employed. By use of the invention I am able to obtain from a given powder charge an increase of approximately 100% in the penetrating capacity of the projectile, as the result of a great increase in velocity, or the same penetration by the projectile with only approximately one-half the previously required powder charge. For example, in the practice of my invention with seventy grains of powder have produced greater penetration than is obtained by the use of 130 grains of powder in the old type of gun having a shear plate at the rear end of the projectile.

It is an object of the invention to provide in the perforation gun of the character described a propelling charge comprising a mass of powder grains and an effective quantity of gaseous medium, (including air) in the propelling charge chamber, at least a portion or" which gaseous medium occupies the spaces existing between the powder grains of the powder mass, and to provide a simple and effective means for exploding 'the powder charge by compression of the entire content of the propelling charge chamber which lies behind the projectile at the rear end of the gun barrel. It is an object oi the invention, hereinafter described in detail as an example only, to provide a projectile ring arrangement wherein a iring charge of powder is placed in the outer part of the gun barrel adjacent the front end of the projectile and the outer end of the gun barrel is closed by a wall which prevents the compression of the firing and propelling charges by hydrostatic pressure encountered in the well, and means are provided for igniting the firing charge so that the pressure developed thereby will drive the projectile rearwardly in the gun barrel against the contents of the propelling charge chamber, which contents include the powder charge and the gaseous elements residing in the propelling charge chamber and which gaseous elements are distributed throughout the small spaces existing between the powder grains of the propelling charge. The interspersed gaseous elements of the propelling charge are thereby compressed in an instantaneous manner, causing a rapid rise in the temperature throughout the entire propelling charge to or above the ignition point of the powder grains of the propelling charge. This causes all of the powder grains, or a very large proportion thereof, to start burning simultaneously and to immediately produce a high propelling pressure, without detonation or such excessive pressure as to cause swelling of the gun body, against the rear face of the projectile to initiate its outward movement. A further object of the invention is to provide in the propelling charge a powder grain size which is determined with relation to the length of time it takes the projectile to travel through the gun barrel, so that the individual powder grains will have a burning time sufriciently long to produce a continued generation of gas to maintain pressure throughout the outward movement of the projectile through the relatively short gun barrel so that a high velocity thereof is developed. A further contribution to the efciency of the perforating gun is the closer approachto complete burning of the powder grains without detonation or rapid burning which approaches close to detonation, by the time the projectile leaves the gun barrel.

It is a further object of the invention to provide a simple and effective means for firing the gun and for preventing application of pressure to powder charges in a gun of the character described, resulting from the lowering of the gun deep into the fluid in a well in which the perforating operation is to be conducted. Accordingly, the desired ignition and burning characteristics of the powder charges yare maintained, the result being that the operating characteristics of the gun are maintained substantially constant, regardless of the different hydrostatic pressures to which the gun is subjected in the well.

It is a further object of the invention to provide a gun of this character having improved means for the electrical ignition of the ring charges associated with the gun barrels.

A further object of the invention is to provide a simple means for holding and igniting the ring charges, these simple means contributing to facility of loading the gun. A further object of the invention is to provide a firing means for a gun of this character which consists of an insertable cartridge.

The present invention is a continuation-in-part of the broad concept disclosed in my copending application, Serial No. 554,105, led September 14, 1944, for Gun Perforator, and relates to subject matter similar to that disclosed in my copending application, now abandoned, Serial No. 626,681, filed November 5, 1945, for Electrically Fired Perforating Gun.

Further objects and advantages of the invention will be brought out in the following part of the specication.

Referring to the drawings which are for illustrative purposes only,

Fig, 1 is a view, to reduced scale, of a preferred embodiment of my invention in a well casing which is to be perforated.

Fig. 2 is an enlarged face view of a small section of the gun body, showing the outer end of one gun barrel and the ring means associated therewith.

Fig. 3 is an enlarged fragmentary sectional view taken as indicated by the line 3-3 of Fig. 2.

Fig. 4 is an enlarged fragmentary sectional view showing the manner in which a cartridge smaller than the gun bore is employed in the ring means.

Fig. 5 is an enlarged perspective sectional view showing one of the electrical ignition elements.

Fig. 6 is a graph comparing my method of ring with other methods.

Fig. 'l is an enlarged fragmentary section of that portion of Fig. 3 indicated by the circle 'I therein.

In Fig. l show a perforator gun I0 embodying my invention suspended within a well casing II by means of an electrical cable I2 which is connected to the upper end of the body I3 of the gun I6 by means of a cable socket Ii, the details of which are not shown due to the fact that these cable sockets are well known in the art, wherein electrically operated or iired devices are lowered into wells.

The body I3 of the gun has on its exterior a spiral channel I5, and along the course of the channel I5, radial openings are bored in the gun body I3 to form gun barrels I6. Although not necessary in all practices of the invention, the gun barrel H3 is shown enlarged at its rear end, in Fig. 3, to provide a powder chamber Il. It will be understood that the powder receiving space lying behind the projectile, regardless of its diameter, constitutes the propelling charge chamber. In the practices of the invention wherein the rear end of the gun barrel I6 is not, enlarged, it will be understood that the space ly- Cil 4 ing between the rear end of a projectile I8 and the inner end wall of the gun barrel or bore I8 constitutes the powder or propelling charge chamber.

As further shown in Fig. 3, the outer end of the gun barrel I6 is counterbored or enlarged to provide a shoulder I9. According to the invention, as shown in Fig. 3 to enlarged scale, a propelling charge of powder 2B is placed in the bottom of the gun barrel i6 so that it will occupy the space designated as the propelling charge chamber il. The projectile I8 is then placed in the gun barrel so that it occupies a position adjacent to the propelling charge 25. The outer end of the gun barrel is then closed by means of a cartridge 2I having a flange 22 which engages the shoulder I9. This cartridge 2l carries a ring charge of powder 23. The cartridge 2l has an end wall 243 which supports the flange 22 and has extending therefrom a cylindric wall 25 defining a chamber for the ring charge 23. The end wall 24 has an opening 2li therethrough to receive an ignition element 2l. This ignition element 2l, as shown to enlarged scale in Fig. 5, comprises a body of plastic dielectric material having a cylindric portion 28 which is a press-fit in the opening 2S of the end wall 2li, Fig. 3, and a flange portion 29 to rest against the outer face of the end wall 24. On the external face of the flange portion 29 there is a nub 3&3, and on the opposite sides of this nub 36 openings SI of small diameter extend through the body of dielectric material, to receive pins 32. The pins 32 are of such close t in the openings SI as to effectively seal the same against passage of fluid through the openings 3l Before the pins 32 are placed in the openings 3| a very fine wire loop 33 is placed so that its end portions 34 extend through the openings 3i after which the pins 32 are pressed into the positions shown in Fig. 5. The wire of the loop 33 has a diameter of only several thousandths of an inch and therefore when the pins 32 are pressed into place, the pins cause embedment of the portions 3Q of the loop in the plastic wall dening the openings 3 I, and the surfaces of the pins 32 make effective electrical contact with the portions 34 of the loop 33. The loop 33 therefore constitutes a filament which will become heated when the outer ends of the pins 32 are connected in series with a source of electrical energy. In Fig. 5 the heads 35 of the pins 32 are shown spaced outwardly from the face of the ange 29 and the nub 30, thereby leaving spaces 3S between the pin heads 35 and the adjacent portions of the nub 30, to receive wires by which electrical connection of a source of electrical energy is made with the ignition element 2l. After such wires are placed in the spaces 36, the pins 32 are forced inward to full extent so that the wires will be clamped by the heads 35 of the pins 32 against the adjacent portions of the nub 3Q, there being then an electrical contact between the wires thus placed and the pins 32 which are in turn electrically connected to the filament loop 33.

As shown in Fig. 3, the filament loop 33 of the ignition element 2l extends into the mass of powder constituting the powder charge 23. This firing charge is retained in the cartridge 2| by the nose 3l of the projectile I8 which has therein a groove 38 adapted to receive the crimped end 35 of the cylindric wall 25, thereby connecting the projectile and the cartridge 2I in a manner reverse from that ordinarily employed in associating a bullet with a shell to form a cartridge. The cartridge unit thus formed simplifies the loading operation. The propelling charge 20 is placed in the chamber II and then the unit consisting of the cartridge and the projectile I8 is placed so that the parts will occupy the positions thereof shown in Fig. 3.

In the ordinary use of the perforating gun, the barrels I6 are loaded in the manner shown in Fig. 3. Sections of rubber insulated Wire 40 are then placed in the spiral channel I5, as shown in Fig. 2, in series arrangement so as to connect all of the loop filaments 33 in series with the electrical conductor III of the cable I2, the uppermost section of wire et, indicated by 4ta of Fig. 1, being connected to the cable conductor 4I, and the lowermost section of the wire 40, indicated by the numeral 4617, is grounded to the metal gun body I3 by a screw t2 disposed in a shallow recess 43 at the lower end of the spiral channel I5. As shown in Figs. 2 and 3, short channels or gates 44 connect the spiral channel I5 with the counterbored recesses Li5 at the outer ends of the gun barrels I6, through which the end portions 46 of the wires i6 may be extended so that the copper conductors 4l' thereof may be connected to the heads 35 of the pins 32 as shown in Fig. 2. The gun Il has thereon spring laments i9 for making electrical contact with lthe casing II to enable use of this casing II as a portion of the series circuit which includes the filaments 33. As shown in Fig. 1, a source of electrical energy, illustrated as a battery 56, is connected to the upper end of the casing II, and the conductor 4I of the cable I2 is connected to a switch 5I which may be closed so as to connect the battery 5U to the wire 40 when firing of the gun I6 is desired.

The following explanation will impart an understanding of the different principles embraced in the invention as compared to the practices followed in the prior art. It will be recognized that when the gun is loaded, the propelling charge 20 and the firing charge 23 are at atmospheric pressure. The cartridge `2I seals the outer end of the barrel I6 and the powder space of the cartridge 2I against increase in pressure other than that which may be caused by a rise in temperature. When the gun Ill is lowered in a well casing which is to be perforated, the water or other liquid in which the gun is submerged exerts a hydrostatic pressure against the gun, but the cartridge ZI seals the outer end of the gun barrel I6 so that the hydrostatic pressure in the well cannot be transmitted to the firing and propelling charges of powder, and therefore the burning rate of the powder, resulting from compression, remains unchanged since hydrostatic pressure cannot reach the interior of the gun barrel.

`When the switch 5I is closed, electric current from the battery passes through the filament 33, heating the same so as to ignite the powder charges 23. The explosion of the powder charge 23 drives the projectile I S rearwardly so as to compress the contents of the propelling charge chamber I'I. The increase in pressure accompanying the reduction in the volume of the contents of the propelling charge chamber I'I, produces an ignition of substantially all of the powder. grains constituting the propelling charge 20, and therefore the generation of gases in the chamber 2'! develops rapidly and continues during the time the projectile I8 is traveling toward the outer end of the barrel I6, the generation of gases from the burning of the many powder grains resulting in a very great acceleration of the projectile I8 and the attainment of a high velocity thereof by the time it leaves the gun 6 barrel I6. As hereinbefore stated, this method of igniting a propelling charge 20 of prescribed characteristics has resulted in an increase in projectile velocity substantially doubling its penetrating ability for a given powder charge without detonating, or pressure rise, tending to seriously swell or injure the gun barrel.

In Fig. 6 I show a graph to illustrate the conditions which I have sought in this invention, and to which I believe I have obtained a close approach, as evident by the superior results attained from the use of the invention. In the graph, Fig. 6, the curve D indicates the pressure conditions developed when a powder is detonated. This is a condition lwherein every powder molecule is converted from solid to gaseous state with great violence, the result being that the wave D rises instantaneously to a peak p, after which the pressure drops off relatively rapidly as shown by the part d of the curve D. This is the condition which develops in a perforating gun wherein the propelling charge is in a highly compressed state, and the burning of the powder, or its Iconversion from solid to gaseous state, is produced by the driving of the projectile against the com pressed powder mass with such force -as to produce detonation. As will be hereinafter pointed out, a feature of my invention consists in maintaining the propelling charge in a relatively loose state so that there will be gas pockets between the powder grains and probably other gas filled spaces in the propelling charge chamber. I have found that where the propelling charge is highly compressed and is set off by detonation, the gun barrel is deformed, for example-swelled or ruptured-due to the fact that the peak p of the detonation pressure wave D produces forces in excess of the elastic limit of the metal of the gun barrel. A purpose of my invention is to avoid destructive conditions such as discussed in the foregoing and to achieve higher projectile velocities than can be obtained by detonation of the propelling charge. Due to the pressure dropoff d of the detonation curve D, full pressure against the projectile which would build up maximum velocity in the projectile is not achieved.

In Fig. 6 the curve R is graphic of the propelling pressure achieved in well perforating guns employing shear plates or flanges at the rear ends of the projectiles to restrain the projectile from outward movement until heavy pressures are developed in the propelling charge chambers of such guns. In this type of gun there is a relatively rapid rise in pressure r until the shear dis-c or flange ruptures. Then, as the projectile moves outward through the gun barrel, there is a lesser rise in the pressure as indicated by the remaining part r' of the curve R.

The curve C of Fig. 6 graphically illustrates the pressure yconditions which, I believe, closely approach my invention. There is :rst a relatively rapid rise c in the pressure exerted in the propelling charge chamber by the simultaneous burning of substantially all of the powder grains until a peak .r is reached, at which time the projectile starts its outward movement. Thereafter, the continued burning of substantially all of the powder grains maintains a nearly constant pressure as indicated by the part :13' of the curve C, lagainst the projectile during its entire travel through the relatively short gun barrel of well perforating guns. As shown in Fig. 6, the product of pressure times distance of projectile travel indicated by curve C is substantially twice that aseo-s r indicated. 'by the' curve: D and-1R; therefore., it would bev expected that a doubling` of the` projectile velocity could:A be achieved under-the-conditions designatedi by the curve C. This expectation is substantiated by the improved-penetration attainable by my invention, as shown' by tests such as referred tofhereinbefore.

In' Fig. 'TI have showna magnified'view of one corner of the propelling charge chamber il", as indicated by the circle 'l or Fig. 3. The propelling charge is placed comparatively loosely inthe chamber il', and consists of powder grains 2li resting in coengagenient, the shapes. of these powder grains, for` example, annular or circular, resulting in the provision of many gas filled spaces s between the powder grains 20 and dispersed throughout the powder massin' the chamber l'i. Also, there are ordinarily larger gas lill-ed spaces (air being included in thev meaning of the term` gas) between the mass of pows der grains and the wall of the chamber i' as indicated at s". The gas content of the propelling charge chamber il, which, in some instances, be nearly as great or may exceed,

the volume or the powder grains 2d', I believe may be properly regarded as a constituent part of the propelling charge since its presence is of great importance to the firing of the powder charge in the manner which I shall hereinafter describe. tion of gas in the propelling lcharge may be much smaller than the normal value indicated in the foregoing and yet achieve the improved results herein taught, but it is my opinion from observation and analysis of operating conditions that a large proportion of gas in the pfllllng Chard@ is indicated for optimum results,

It is a purpose of my invention to produce a surface ignition of each powder grain 2G', so that the powder grains 2G will simultaneously evolve propellant gas in the chamber l'i, instead or igniting the powder by starting the burning of grains at one side or the charge, and instead of detonating the grains. To produce this result of surface ignition of substantially all oi the powder grains at the same time, I utilize the phenomenon of heat concentration or heat generation by the compression of a gas. As an example of what is meant, page-178 of Analytical Experimental Physics, University of Chicago Press, 1943, points out that if a mass of air at Zero degree centigrade, conilned to a perfectly insulating cylinder so that no heat is lost to the environment, is compressed to one tenth its original Volume, its temperature will rise at 429 C. It is quite evident that this temperature exists throughout the entire volume of compressed gas. Therefore, by compressing the propelling charge 20, Fig. 7, having a gas content, I produce a heat concentration or generation throughout the' entire volume of gas and develop in the gas spaces adjacent the surfaces of the powder grains 253'K temperatures which produce surface ignition of the powder grains' 2e so that they start to burn and evolve gas until the burning eiect has entirely consumed the entire powder grains. It is recognized, of course, that there is a transfer of heat from the gas to the powder grains and that there is an absorption of heat by the metal of the body i6 forming the chamber il; therefore, it is necessary tov produce in the propelling charge 2li a compression greater than ten atmospheres. In the practice 0f the invention, I compress the gassurrounding the powder grains not less than twenty or thirty atmospheres to raise It will be understood that the por- (ill 8. its'temperature and therefore the surface-of the grains-in contact with-it, to such temperature that ignition` of the powder w-ill take placel in about 02.0921 second. It will be seen therefore thatit does not require a very large charge of powder in the cartridge 2li,- Fig. toA drive the projectile lS rearward withsuch-force as to-produce a compression; of the gas content ofA the propelling chargev 20 which will result inV ignition temperatureson the surfaces of the powder grains. From a theoretical standpoint, it is regarded that the compression. of the gas content of the propelling charge occurs-in. such a short space of time that ignition temperatures are created on the surfacesl of the powder grains and the burning of tlie powder grains is started before the powder grains have had time to absorb any great amount of heat,. and that therefore the powder grains burn at av controlledI rate. However, the fact that all of the powder grains are burning simultaneously evolves sui'licient gas to instantaneously produce the pressure risc c of the curve C and to maintain the continued pressure during the travel of the projectile through the gun barrel.

With ne grain powder, my invention achieves improved results, but it is a feature of the invention to determine the grain size of the powder with relation to the length of the gun bore or the length of time required for the projectile to travel through the gun bore, so that the powder grains will not be consumed before the projectile leaves the gun barrel, but will continue to supply propelling pressure for the projectile throughout its. entire travel through the barrel, thereby maintaining a close approach to maximum velocity for the size and characteristics of the powder charge employed.

In Fig. 3 I have shownl a form of the invention wherein the. cartridge 2| has a diameter or gauge the same as that of the gun barrel I6. In Fig. l I show the manner in which a smaller cartridge 2li may be used in the gun barrel or wherein the gun barrel is of a diameter larger than; the diameter of the cartridge. In Fig. iv the cartridge 2i has all of the characteristics of the cartridge 2l shown in Fig. 3, with the exception of its size relative to the gun barrel i6. The cartridge 2 is supported in an adaptor ring Eil having a cylindric wall 6l which extends into the outer end of the barrel IE- andv is provided with an openingl E2 which receives the cartridge in press-fit relation. The adaptor ring 60 has a iiange portion 63 to engage the shoulder I9. In this practice of theV invention the powder charge of the cartridge 2l' is supplemented by powder 65 placed in the barrel I5 between the cartridge-2i and the' projectile i8, someA of this powder 65 also surrounding that portion of the cartridge which projects rearwardly froml the adaptor ring S0; The use of the cartridge 2l" serves as a means for reasonable assurance of thetiiring of the nring charge 23. The powder of the firing charge 23 is placed in the cartridge 2i or 2i" after the installation of the ignition element 2T, so that the powder completely encloses the filament and the powder is packed in the cartridge with sufficient rmness to hold many powder grains in" contact or in close proximity with the lament 33, so that when it becomes electrically heated', thev powder charge will be ignited.

I claim as my invention? l. In a gun of the character described,. whereinta propelling charge is red by drivingthe projectile rearwardly so as to compress the propelling charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propelling charge in said chamber; a projectile in said barrel spaced from the outer end of said barrel; a wall closing the outer end of said barrel to prevent entry thereinto of external pressure; a iiring charge between said projectile and said wall, said wall comprising a body of dielectric material, said bodi7 having spaced openings therethrough for pins; a loop lament in the space between said wall and said projectile, the end portions of said lament being extended into said openings; and pins inserted into said openings to hold said end portions of said filament therein.

2. In a gun of the character described, wherein a propelling charge is fired by driving the projectile rearwardly so as to compress the propelling charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propelling charge in said chamber; a projectile in said barrel spaced from the outer end of said barrel; a wall closing the outer end of said barrel to prevent entry thereinto of external pressure; a iiring charge between said projectile and said wall, said wall comprising a body of dielectric material, said body having spaced openings therethrough for pins; a loop lament in the space between said wall and said projectile, the end portions of said filament being extended into said openings; and pins inserted into said openings to hold said end portions of said iilament therein, said pins having shoulders on 'the outer ends thereof for clamping external conductors against the outer face oi said body, thereby making electric connection between the conductors and the pins.

3. In a gun of the character described, wherein a propelling charge is fired by driving the projectile rearwardly so as to compress the propelling' charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propeiling charge in said chamber; a projectile in said barrel spaced from the outer end of said barrel; a wall closing the outer end of said barrel to prevent entry thereinto of external pressure; a firing charge between said projectile and said wall, said wall comprising a body of dielectric material having a nub on the exterior thereof, there being pin openings through said body adjacent said nub; a loop lament in the space between said wall and said projectile, the end portions oi said filament being extended into said openings; and pins inserted into said openings to hold said end portions of said filaments therein, said pins having shoulders on the outer ends thereoi roi' clampig external conductors against the outer race of said body adjacent said nub, thereby making electric connection between'the conductors and the pins.

1i. In a gun ci the character described, wherein a propelling charge iired by driving the projectile rearwardly so as to compress the propelling charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propelling charge in said chamber; a projectile in said barrel spaced from the outer end ci said barrel; a wall closing the outer end oi said barrel to prevent entry thereinto of external pressure; a rlng charge between said projectile and said wall, said wall comprising a body of dielectric material, said body having spaced openings therethrough for pins; a filament in the space between said wall and said projectile for igniting said firing charge; and pins in said openings for making electrical connection with said filament.

5. In a gun of the character described, wherein a propelling charge is iired by driving the projectile rearwardly so as to compress the propelling charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propelling charge in said chamber; a projectile in said barrel spaced from the outer end of said barrel; a wall closing the outer end of said barrel to prevent entry thereinto oi external pressure; a iiring charge between said projectile and said wall, said wall comprising a body of dielectric material, said body having spaced openings therethrough for pins; a llament in the space between said wall and said projectile for igniting said ring charge; and pins in said openings for making electrical connection with said iilament, said pins having shoulders on the outer ends thereof for clamping external conductors against the outer face of said body, thereby making electric connection between the conductors and the pins. c

6. In a gun of the character described, wherein a propelling charge is ired by driving the projectile rearwardly so as to compress the propelling charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propelling charge in'said chamber; a projectile in said barrel spaced trom the outer end of said barrel; a wall closing the outer end'of said barrel to prevent entry thereinto of external pressure; a ring charge between said projectile and said wall, said wall comprising a body oi dielectric material having a nub on the exterior thereof, there being pin openings through said body adjacent said nub; a filament in the space between said wall and said projectile for igniting said firing charge; and pins in said openings for making electrical connection with said filament, said pins having shoulders on the outer ends thereof for clamping external conductors against the outer face of said body adjacent said nub, thereby making electric connection between the conductors and the pins.

7. In a gun of the character described, wherein a propelling charge is red by driving the projectile rearwardly so as to compress the propelling charge, the combination oi: a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propelling charge in said chamber; a projectile in said barrel spaced from the outer end of said barrel; a cartridge closing the outer end of said barrel soY asto prevent entry of external pressures into said barrel, there being a ring charge in said cartridge; electric igniting means for said ring charge in said cartridge; and means extending through the end wall of said cartridge for conducting electric current to said igniting means.

8. In a gun of the character described, wherein a propelling charge is red by driving the projectile rearwardly so as to compress the propelling charge, the combination of: a gun. structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propelling charge in said chamber; a projectile in said barrel Yspaced trom the outer end of said barrel; a -cartridge-closing the outer end of said barrel so as to prevent entry of vexternal pressures into said barrel, there being a :firing charge vin said cartridge; a lament in said cartridge for igniting said firing charge; and means extending through the end wall of said cartridge for connecting said lament 'with a source of electric current.

9. In a gun of the character described, wherein a propelling charge is red by driving the pro- :jectile rearwardly so as to compress the propelling charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber communicating 'with its Vrear end; a a.

.propelling charge in said chamber; a projectile in vsaid barrel spaced from the outer end of said barrel; a cartridge closing the outer end of said barrel so as to prevent entry of external pressures vinto said barrel, there being an explosive in f said cartridge; electric igniting means for said explosive in said cartridge; and means extending through the end wall of said cartridge for conducting electric current to said igniting means.

v1i). In a gun of the character described, wherein a propelling Ycharge is fired by driving the projectile rearwardly so as to compress the propelling charge, the combination of; a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; la propelling charge in said chamber; va projectile in said barrel spaced from the outer end of said barrel; a cartridge closing the outer end of said barrel so as to prevent -entry of external pressure thereinto, there being an explosive `in said cartridge and said cartridge `comprising ran end wall of dielectric material having pin openings therethrough; igniting means in said .cartridge for said explosive; and vpins extendingthrough said openings for connecting'said igniting means with a source of electric current.

1l. In a gun of the character described, wherein a propelling charge is fired by driving the projectile rearwardly so as to compress the propelling charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propelling charge in said chamber, said propelling charge comprising a mass of powder grains interspersed with a gaseous medium, the size of said powder grains being determined with relation to the time required for said projectile to move through said barrel; a projectile in said barrel spaced from the Youter end of said barrel; means for preventing external pressure from moving said projectile so as to apply pressure to said propelling charge; and means for driving said projectile rearwardly insaid barrel so as to compress the contents of said propelling charge chamber to ignite said propelling charge.

Yl2. In a gun of the character described, wherein a propelling charge is fired by driving the projectile rearwardly so as to compress the propelling charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propelling charge in said chamber; a Yprojectile in said barrel spaced from the outer end of said barrel; a cartridge closing the outer end of said barrel so as to prevent entry of external p-ressures into said barrel, -there being a ring charge in said cartridge; and means for ring said ring-charge in said cartridge so that the force from :the explosion of vsaid ring charge will be delivered .into the outer end Aof said barrel.

v13. In a gun of the character described, wherefifn a ,propelling charge kis fired by driving the projectile rearwardly so as to compress the propelling charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber communicating with its rear end; a propelling charge in said chamber; a projectile in said barrel spaced from the outer end of said barrel; a cartridge havingits open end communi- `eating with `the outer portion of said barrel, ,there being -a ringcharge in said cartridge; electric igniting means for said firing charge in said cartridge; and means extending through the end wall of said cartridge for conducting electric current to said igniting means.

14. In a gun of the character described, wherein a propelling charge is red by driving the projectile rearwardly so as to compress the propelling charge, the combination of: a gun structure having a gun `barrel and a propelling charge chamber communicating with its rear end; a propelling charge in said chamber; a projectile in said Vbarrel spaced from the outer end of said barrel; a cartridge having its open end communicating with the outer portion of said barrel, there beinga ring charge in said cartridge; and means for firing said ring charge in said cartridge so that 'the'force from the explosion of said firing charge will be delivered into the cuter end of said barrel.

15. lIn a gun of the character described, wherein va propelling charge Ais red -by ydriving the projectile rearwardly so Vas to compress the propelling charge, the combination of: a gun structure having a gun barrel and a propelling charge chamber Ycommunicating with its rear end; a propelling charge in said chamber; va projectile in said barrel spaced from the outer end of said barrel; a cartridge having at least a portion thereof extending into said barrel, said cartridge being Vattached to the front portion of said projectile and there being a firing charge in said cartridge; :and means for firing said ring charge in said cartridge so that the force from the explosion of said ring charge will be delivered against the front end of said projectile.

16. A gun .perforator comprising: a gun body structure dening a plurality of gun bores; bullets inthe gun bores; propellent explosive means rearwardly of the bullets; cartridge means in each gun bore in front of the bullet therein, each of said cartridge means containing an explosive charge and electric current responsive ignition means.

1'?. In 'a gun perforator, a gun body structure defining a gun bore; a bullet in said gun bore; propellent explosive means,` rearwardly of the bullet; explosive means in said gun bore in front of the bullet; a container for said last-named explosive means; and means associated with said container for-sealing said gun bore.

18. In a gun perforator, a gun body structure j dening a gun bore; a 'bullet in said gun bore;

propellent explosive means rearwardly of said bullet; cartridge means in said gun bore in front of said bullet, said cartridge means containing an explosive charge and ignition means therefor; and means adjacent the forward end of said cartridge means for sealing said gun bore.

19. In a gun perfcrator, a gun body structure dening a gun bore; a bullet in said gun bore; propellent explosive means rearwardly of said bullet; cartridge means in said gun bore in front oi' said bullet and containing an explosive charge and ignition means therefor; means forming a shoulder associated with said cartridge means; and complementary shoulder means on said gun body structure cooperating with said first-named shoulder to limit inward movement of said cartridge means in said gun bore.

20. A gun perforator comprising: a gun body structure dening a plurality of laterally directed gun bores; bullets in said gun bores; propellent explosive means rearwardly of said gun bores; explosive means in said gun bores in front of said bullets, each of said last-named explosive means comprising a, fluid-tight cartridge containing an explosive charge and electric current responsive ignition means; and current conductor means extending along the outer Wall of said gun body structure and connected to each of said ignition means.

2l. For use in a gun of the character described wherein a propelling charge is fired by exploding a ring charge in the outer portion of a gun barrel so as to drive a projectile rearwardly to compress the propelling charge: a wall arranged for closing the outer end of said barrel to prevent entry thereinto of external pressure; said Wall comprising a body of dielectric material, said body having spaced openings therethrough for pins; a loop lament in the space between said wall and said projectile, the end portions of said mangent being extended into said openings; and

pins inserted into said openings to hold said end portions of said filament therein.

22. For use in a gun of the character described wherein a propelling charge is fired by exploding a ring charge in the outer portion of a gun barrel so as todrive a projectile rearwardly to compress the propelling charge: a wall arranged for closing the outer end of said barrel to prevent entry thereinto of external pressure; a cartridge for closing the outer end of said barrel so as to prevent entry of external pressures into said barrel and for holding a firing charge in said barrel; a lament in said cartridge for igniting said ring charge; and means extending through the end wall of said cartridge for connecting said lament with a source of electric current.

PHILIP W. MARTIN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,376,530 Greener May 3, 1921 1,470,591 Behar Oct. 16, 1923 FOREIGN PATENTS Number Country Date 24,755 Great lritain T" Oct, 13, 1362

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