US 3850101 A
A firearm cartridge adapted to be fired electrically including a generally cyclindrical primer introduced through the open end of a metal casing and press fit into a passage extending axially through its base. One end of the solid metal primer body, facing rearwardly in the passage adjacent the external surface of the base, is tapered so that the primer seats against a correspondingly narrowed portion of the passage, while the opposite end projects forward of the base into the main propellant charge. An insulated conductor extends through a longitudinal bore in the primer body from the one end into a cavity within the opposite end filled with primer compound, at which point the conductor terminates in a ball larger in diameter than the bore. Electrical contact is made with the conductor by trigger pull to ignite the primer compound. Back pressure from the resultant initiation of the propellant charge urges the primer body against the passage wall to form a seal.
Claims available in
Description (OCR text may contain errors)
[ Nov. 26, 1974 Primary Examiner-Benjamin A. lBorchelt Assistant Examiner-C. T. Jordan Attorney, Agent, or Firm-Robert M. Betz; Richard A. Bachard  ABSTRACT A firearm cartridge adapted to be fired electrically including a generally cyclindrical primer introduced through the open end of a metal casing and press fit into a passage extending axially through its base. One end of the solid metal primer bodly, facing rearwardly in the passage adjacent the external surface of the base, is tapered so that the primer seats against a correspondingly narrowed portion of the passage, while the opposite end projects forward of the base into the main propellant charge. An insulated conductor ex- Vernon K. Sower, Box 91, Bayfield, Colo. 81122 July 26, 1973 References Cited UNITED STATES PATENTS United States Patent [191 Sower ELECTRICAL PRIMER  Inventor:
21 Appl. No.: 383,033
 Field of yd s W mm wmmm b no kmm e m mma m mam a w mm ma e p ee m nm m mmhm r nn s m mhmnm etw O a r. .wg m aem m mm m m iO i uap tew 2 t ma e a 6 0 a hm m 8 2 nmc. m n 9 2 2 3 0.1 lotsp l 2 d cmm 3 an wl C r mwmm a 9 mm mmu s I 1 )4 mwmi mw I mmn wcm m d is??? t. .,.....,.W.,/ 7 mmmawmwaw t 00% )0. 2 6666 666 t .f V V V 4444 444 k many new WNW mmwm mwm a s ambit m n 0 x\ A "Fulfill 0V, .9 5 m a a n I 3 m P I I ui; .n.n m m Mmw V ma mma 3 e T 686 l I 0 aa aw mama o 2 m 2 T I U 1 8 A736 6666 P890 wwww mmw m ww w I E 0315 R000 9346 0977 ,35 F 6823 434 8296 2 ,2 2333 ELECTRICAL PRIMER BACKGROUND 1. Field of Invention This invention relates generally to the field of firearm cartridges and more particularly to such cartridges which are adapted to be fired with the passage therethrough of an electric current.
2. Description of the Prior Art Among sportsmen and also in military situations, the muzzle velocity of a bullet fired from a rifle or handgun is an important consideration in achieving range and kill power. The limiting factor in such muzzle velocity for a weapon of a given caliber is found to be the inter nal pressure which may be safely generated within the cartridge itself. This may be controlled,'of course, by the amount and type of propellant charge introduced, but it is also determined in part by the mechanical strength of the cartridge. If the casing fails to resist the internal pressure generated, such pressure may escape backwardly against the bolt body rather than simply propelling the bullet down the gun barrel, thus endangering the integrity of the weapon and the safety of the operator.
The conventional self-primed mechanically fired cartridge includes a metal casing with a forwardly extending pocket in the base which is adapted to receive a primer. A small flash hole is provided in the base through which gases from the ignited primer compound pass to initiate the main propellant charge. When the firing pin strikes the base of the primer, it partially ruptures its surface, lessening its resistance to backward pressure passing through the flash hole. The corners of the primer also tend to be swaged against the bolt face including further stress weakening at these points. The initiation process would be accomplished more rapidly and uniformly if the interface between the primer compound and the propellant charge were extended over a larger cross-sectional area, but this would further degrade the sealing efficiency of the primer because of the greater area over which backward pressure could develop.
Electrically fired cartridges have been designed which provide greater contact area between the primer compound and the propellant charge, but they still fail to provide a completely effective pressure seal. Such electrically initiated firearm cartridges are well known in the art. Typically, they employ a conductor extending within a quantity of propellant initiating material which in turn sets off the main propellant charge. The conductor may be oriented such that by operating a trigger an electric current is passed through the conductor to ignite the propellant initiating material. The disadvantage of the prior art construction lies in the fact that in common with the cartridges fired mechanically by means of a firing pin, the base of the casing is not well adapted to containment of the high pressures generated within the cartridge with initiation of the main propellant charge. One reason for this appears to be that while the main body of the casing has an unbroken surface the base usually supports a separate straight-walled primer body inserted therein externally. In the absence of any positive sealing means pressure escapes between the wall of the primer body and the base and thus limits the pressures which may safely be generated. This in turn serves to limit the muzzle velocity of a given cartridge.
For example, in Martin et al, U.S. Pat. No. 1,485,404, a cylindrical insulating plug in the base of the cartridge body forms, in effect, the primer body surrounding a contact pin leading to a primer compound. It is apparent that upon electrical initiation of the main powder charge this insulating plug will tolerate less internal pressure than the main cartridge body and consequently becomes the weakest part of the structure.
Another example of an electrically fired weapon is found in Clay U.S. Pat. No. 3,009,419 wherein a cylindrical metal primer cup is inserted in the base of a cartridge case. Again, upon initiation of the main propellant charge the integrity of the interface between the cup and the case limits the internal pressures which may be achieved.
The prior art recognizes the fact that the bottom or base of a firearm cartridge is placed under severe stress with the high pressures generated in such cartridges, as for example in Stadler U.S. Pat. No. 3,611,939. However, this patent focuses on a selection of priming compositions and booster material within the primer body which minimizes the pressures generated before the ignition of the main propellant charge, rather than on a redesign of the primer itself.
SUMMARY OF THE INVENTION It is, therefore, the general object of this invention to provide a firearm cartridge having an improved capability to withstand internal pressures.
It is a related object of this invention to provide a firearm cartridge of such improved pressure resistance characteristics which is adapted to be fired electrically.
It is a still further object of this invention to provide a cartridge adapted to be electrically fired by operation of a trigger mechanism which is capable of safely achieving significantly higher muzzle velocity with a given caliber of weapon.
It is yet another object of this invention to provide a firearm cartridge with a base mounted primer adapted to be substantially self-sealing upon ignition thereof.
In accordance with the preferred embodiment of this invention, a solid metallic, generally cylindrical primer body is inserted through the front end of a cartridge casing and embedded in an axial passage extending through the base of the casing. The passage narrows toward the external surface of the base in the form of a truncated cone and the primer body has a correspondingly shaped portion at its rearward end which interfaces with the wall of the narrowed section of the passage. The front end of the primer body which is in contact with the propellant charge filling the main hollow body of the casing, is provided with an open cavity filled with propellant initiating material. An electrical conductor surrounded by a suitable dielectric extends axially through a bore in the primer body from the rearward end thereof into the cavity and terminates in contact with the propellant initiating material. A metal ball of diameter larger than the bore through the primer body caps the end of the conductor in the cavity. The dielectric material covers the base of the cavity so that the shortest conductor path from the ball to the adjacent wall of the primer body is laterally through the propellant initiating material. A the narrowed rearward end of the primer body, the conductor bore flares outwardly to increase the length of the path between the conductor and the primer body at its external surface.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal section through a cartridge casing in accordance with this invention.-
FIG. 2 is a detail of the electrically actuated primer of this invention positioned within the base of the cas- 1ng.
DETAILED DESCRIPTION In accordance with the preferred aspect of this invention as seen in FIG. 1, an electrically actuable primer is adapted to be press fitted within a base 11 of a metal firearm cartridge casing 12 having a hollow tubular body portion 13 containing a propellant charge 14 and a narrowed neck 15 adapted to support a bullet 16.
The construction of the primer 10 and its relation to the base 11 is more clearly understood with reference to the detail of FIG. 2. A solid metal primer body is embedded within a passage 21 extending axially through the base 11, so that the side wall of the primer body 20 within the passage 21 has a contiguous interface with the material of the base 11. The primer body 20 is generally cylindrical, but at its rearward end it is provided with a beveled or tapered portion 22 preferably shaped in the form of a truncated cone with its flattened apex flush with the external surface of the base 11. The wall of the passage 21 has a mating tapered surface 23 against which the tapered portion 22 is. adapted to bear. The front or inner end of the primer body 20 is hollowed out to form a cylindrical cavity surrounded by side walls 25, which is filled with a suitable propellant initiating material or primer compound 26. The inner end of the primer body may conveniently extend forward of the inner surface of the base 11 into the main propellant charge 14. Except for a thin paper retainer 27 covering the front end of the primer body 20 the propellant initiating material 26 is in substantial contact with the propellant charge 14 over the entire inner diameter of the primer body 20.
The primer body 20 is drilled longitudinally to receive an electrical conductor 29, the rearward end of which is exposed to the external surface of the base 11 while the forward end terminates within the propellant initiating material 26 in the primer cavity. A metallic ball caps the forward end of the conductor 29, its diameter being chosen such that its exceeds that of the axial bore 28 which carries the conductor 29. A sheath of high tensile strength dielectric material 31 surrounds the conductor 29 separating and insulating it from the primer body 20. The conductor carrying bore 28 is provided with an outwardly flared portion 32 of predetermined taper which extends to the rearward end of the primer body 20 where it is substantially flush with the external surface of the base 11. The dielectric material 31 fills this flared portion 32 and also covers the bottom 33 of the frontal cavity in the primer body 20.
By means well known in the art, a high voltage electrical impulse may be applied, simultaneously with trigger pull, to a conductor such as conductor 34 connected to positive contact 17 extending, protected by suitable insulation 35, to the forward surface of a firing bolt 36 which interfaces with the external surface of the base 11. The conductor 34 is thereby placed in contact with the rearward end of the conductor 29 of the primer 10. Current through the conductor 29 ignites the propellant initiating material 26 which in turn initiates the propellant charge 14 to cause discharge of the weapon. The internal pressure within the casing 12 will drive the solid primer body 20 in a rearward direction so that the tapered portion 22 wedges tightly against the correspondingly tapered surface 23 to produce a highly effective pressure seal. At the same time, if the dielectric material 31 covering the bottom 33 of the primer cavity is displaced, the ball 30 will be urged toward the mouth of the conductor carrying bore 28 and block possible pressure loss along this path. The dielectric material 31 at the bottom of the cavity 33 serves also to eliminate the possibility that a spark may jump from the base 30 to the primer body 20 without passing laterally through the main body of propellant initiating material 26, thus shorting out the system.
In order to further increase the length of the-arc path to the primer body 20 at the interface between conductors 29 and 34 provided by the flared portion 32 of the bore 28, a central disc shaped depression 37-can be formed in the external surface of the primer 10 to accommodate the forward end of the conductor 34 and its surrounding insulation 35.
It is important to appreciate that the shape of the primer body 20, in cooperation with the corresponding shape of the passage 21, provides an automatic self sealing action responsive to propellant initiation and thus insures that the interface between the primer body 20 and the casing 12 will not constitute a weak point in the pressure retaining ability of the cartridge. The primer 10 of this invention is well adapted to removal and reinsertion in connection with hand loading operations. The outer diameter of the primer 10 is preferably slightly less than the inner diameter of the neck 15 and after passing this stage it will easily slide down the body portion 13 and position itself generally within the mouth of the passage 21 where it can be press fit and seated firmly in place.
The material of the primer 10 is not critical, although it may, for example, be constructed of brass positioned within a stainless steel casing 12. The important consideration is that the coefficient of thermal expansion of the primer 10 and the casing 12 should be sufficiently close so that in extreme environmental conditions the interface between the two will not separate substantially. The particular angle of the taper on portion 22 and surface 23 is also not critical, although clearly the degree of wedging action that will be achieved therebetween will be dependent upon this angle.
The material selected for the dielectric 31 should preferably be a semi-rigid epoxy resin which will form a good bond, both with the conductor 29 and the inner surface of the axial bore 28.
The applicant has performed tests with an electrically fired primer constructed in accordance with this invention, using a 308 Norma Magnum'rifle with a case fabricated from 303 stainless steel. Test results were as follows:
Test Number I 130 grain bullet 72.5 grains H380 powder Temperature 40F Velocity 3,367 feet per second Velocity converted to 70F of 3,428 feet per second Test Number II 130 grain bullet 55 grain H335 powder Temperature 40F Velocity 2,882 feet per second Velocity converted to 70F of 2,924 feet per second Test Number III 130 grain bullet 84.0 grains H335 powder Temperature 40F Velocity 3,937 feet per secon Velocity converted to 70F of 4,033 feet per second Test I was for control purposes. A cartridge modified in accordance with this invention was found to yield muzzle velocities very close to the published figures employing conventional cartridges using the same caliber of bullet and type and weight of powder. Thus, the results of Test I strengthen the reliability of the conclusions reached from Tests II and III. The latter two tests both employed a type of powder which is not within a safe range for the given test weapon with conventional cartridges. After these test firings, it was observed that the cartridge casing showed no damage and the primer did not leak gas. The velocity which was achieved with, Test III is between and 30 percent higher than that obtainable with conventional ammunition for the test weapon.
Incorporation of the primer of this invention in a cartridge employing a bullet of given caliber and make will require additional experimentation to determine the safe powder load in individual cases. Additional consideration must also be given to the strength of the gun barrel and the chamber which will be employed. It is important to understand, however, that the incorporation of this invention does not require any modification of the basic shape or configuration of a conventional cartridge. All these matters are well within the skill of the art.
It should be additionally understood that the foregoing detailed description and drawings are intended to be illustrative only and that various modifications in the structure and interrelationship of the component parts as set forth as well as in the materials thereof may be made without departing from the scope and spirit of this invention more particularly set out in the appended claims.
What is claimed is:
1. In a firearm cartridge having a metal casing, including at least a base and a hollow tubular body portion integral with said base containing a propellant charge, an electrically fired primer comprising:
a. a solid cylindrical metal primer body having a cavity in one end thereof and an axial bore connecting said cavity to the opposite end thereof, a portion of said primer body being of reduced diameter;
b. a propellant initiating material filling said cavity;
c. an electrical conductor extending from said opposite end through said bore into contact with said propellant initiating material; and
d. a dielectric material filling the space between said conductor and the wall of said bore, said primer body being adapted to extend slidably within an axial passage through said base so that said one end lies within the propellant charge and said opposite end is adjacent the external surface of the base, the wall of said passage having an interface with said reduced diameter portion of said primer body.
2. A device as in claim I wherein the reduced diameter portion of said primer body is in the form of a truncated cone with its flattened apex at said opposite end.
3. A device as in claim 1 additionally comprising a conductive ball capping the conductor within the cavity and having a diameter greater than that of said bore.
4. A device as in claim I wherein said dielectric material extends within said cavity so that the shortest conductive path between said ball and said primer body is through said propellant initiating material in a lateral 'cliidinga base closingone end thereof, and a hollow tudirection.
5. A device as in claim 1 wherein said bore has an outwardly flared section of predetermined taper adjacent the opposite end of said primer body.
6. A device as in claim 5 wherein a predetermined length of the conductor at said opposite end, together with the surrounding dielectric material, are removed to form an axially extending cylindrical depression at.
said opposite end.
7. In a firearm cartridge having a metal casing, in-
bular body portion integral with said base containing a propellant charge, an electrically fired primer comprising:
a. a cylindrical metal primer bodly;
b. a quantity of propellant initiating material confined adjacent one end thereof;
c. conductive means extending from within said propellant initiating material to the opposite end of the primer body, said opposite end being of reduced diameter;
d. means for insulating said conductive means from said primer body, said primer body being adapted to fill an axial passage through said base, so that said one end extends within the propellant charge and said opposite end extends to the external surface of the base.
8. A device as in claim 7 wherein said primer is adapted to be slidably inserted in said base from within .said casing.
9. In an electrically actuated firearm cartridge having a metal casing including a base and a hollow tubular body portion integral therewith containing a propellant charge, the improvement wherein a. said base is provided with an axial passage extending therethrough, said passage having a first cylindrical portion extending rearward from the internal surface of the base and a second portion of reduced diameter extending from said first portion to the external surface of said base.
7 8 b. a solid primer body adapted to fill said passage, and I Said P m y haying Wlthin one end e. dielectric means adapted to separate said conducthereof in contact with said propellant charge; five means f id primer body, whereby upon c. a propellant initiating material filling said cavity;
d. conductive means extending from within said propellant initiating material to the opposite end of said primer body and adapted to transmit an ignit- 0nd Portion of the Passage in Said base ing current to said propellant initiating material;
electrical initiation of said propellant charge said primer body is wedged against the wall of the sec-