It is known in the art to use targets comprised of conductive layers or electrodes which are separated by an insulator. These electrodes are electrically connected subsequently by a metal projectile which penetrates the target during use and spans the insulation connecting the two electrodes for a split second and causing a short to occur thereby. Upon penetration of a projectile or bullet into the target layers, the metal bullet or projectile removes the insulator from its path and physically connects the electrodes causing an electrical short which is immediately indicated on appropriate display, monitor or the like.
There are U.S. patents which generally disclose systems and targets of this nature such as U.S. Pat. Nos. 2,819,084; 3,401,939; 3,454,277; and 4,240,640. In U.S. Pat. No. 2,819,084 (Brown) an electrically scoring target is disclosed constructed of two metallic screen electrodes separated by a rubber diaphragm. The electrodes of the Brown target are connected to a remote scoring indicator via a conductor wire which is connected to a screen. The scoring target by means of electrical relays will indicate whenever a short circuit is caused between Brown's metallic screens by the passage therethrough of a metal projectile. When using a target with two screens as in Brown, there is a high probability of causing a continuous short which would destroy the reusability of the target.
In La Mura U.S. Pat. No. 53,401,939 (La Mura I) a target is disclosed having two metal foil layers separated by a foam layer, and also having foam layers on the opposite face of each foil. The metal foil layers are displaced by the projectile and form a connection between these foil electrodes so that current can pass between them and be recorded by means of an external circuit. FIG. 4 of La Mura I illustrates a circuit means that is used in conventional systems of this type, and which is also applicable to the present invention. A potential problem encountered with the use of two metal foils is in using a foil as the back conductive layer there is poor reliability for low caliber bullets and airgun ammunition. The back insulating layer is so soft that it does not offer any resistance to the force of the projectile. This insulating layer does not contract to the maximum, restricting the usage of the target with only medium or large caliber projectiles. In this type two foil electrode target we found that when using airgun ammunition the failure of the target was continuous.
In La Mura U.S. Pat. No. 3,454,277 (La Mura II), like in Brown above discussed, a projectile shorting target with two wire screen electrodes is disclosed. La Mura II's target is comprised of two aluminum wire screens separated by an insulator material. A difficulty in utilizing this type target is the high probability of causing a continuous short resulting in the complete failure of the target. It is important in any target system of this type to have the ability to register small caliber projectiles and to accomplish this the intermediate insulating layer must be relatively thin. That is, the distance between the two electrodes must be small enough to be spanned by the small caliber projectile. When two electrode layers of wire are used together with a narrow insulator to separate them, the small wires of the front layer will puncture the thin insulating material and make a constant short with the back electrode layer. This problem can only be overcome by increasing the width of the intermediate insulating layer which then as noted above renders the target non-functional with small caliber such as airgun ammunition. Thus, La Mura II would either not function with small caliber ammunition or would be constantly shorted out because of contact by the front wire electrode with the back wire electrode.
In La Mura III, La Mura acknowledges that La Mura I and La Mura II are not satisfactory when he notes in column 1 of La Mura III when referring to his La Mura I and II, ". . . they possess important drawbacks and disadvantages, etc. . . . not only is the frequency of shorting between the electrodes after the traverse of the target by a projectile undesirably high necessitating the frequent electrical burning of the shorts or the discarding and replacement of the target, etc. . . . are of limited application and often unreliable and inconvenient to use and otherwise leave much to be desired." To correct these "frequency of shorting" problems presented by his earlier patents, La Mura III proposes the use of two resin coated aluminum wire screens separated by an insulation layer. There are two difficulties associated with using this type target. The first difficulty is identical with that noted above in reference to La Mura II. That is, a constant short will occur between the two wire screens almost immediately after shooting the target with medium or small caliber ammunition since the front electrode is a screen. This will render the target non-reusable. The second difficulty is caused by the coating of the wire screens. As indicated in La Mura III, this coating improves the reliability and durability of the target for large projectiles. However, La Mura III's target decreases the reliability almost to zero for small caliber projectiles like airgun ammunition and/or 0.22 caliber.
There is therefore a need for an electrically responsive target that is reliable, has a substantially long reusable life, and can be used with all size ammunition including small caliber projectiles.