EP1366338A1

EP1366338A1 - Shotgun shot, pellets and bullets

Info

Publication number: EP1366338A1
Application number: EP02703720A
Authority: EP
Inventors: Arthur Hugh Godfrey Phillips
Original assignee: Lyalvale Ltd
Current assignee: Lyalvale Ltd
Priority date: 2001-02-28
Filing date: 2002-02-28
Publication date: 2003-12-03
Also published as: GB2372800A; GB0204672D0; WO2002068897A1; GB2372800B; GB0104949D0

Abstract

A shotgun shot, pellet or bullet is made of an alloy containing bismuth, tin and 2% to 5% by weight copper. Preferably the alloy contains less than 50% by weight bismuth. In a preferred embodiment the content by weight is 45% bismuth, 52% tin and 3% copper. The inclusion of the copper in the alloy simplifies the manufacturing process of the shot, pellet or bullet as compared with known bismuth and tin alloys. Shot or pellets may be formed by short or long drop forming and bullets may be formed in conventional bullet moulds. The ballistic performance of shot made from the alloy is good and for bullets from the alloy is comparable with that of copper coated lead bullets.

Description

SHOTGUN SHOT, PELLETS AND BULLETS

This invention relates to shotgun shot, pellets and bullets.

Each year many thousands of tonnes of lead alloy shotgun pellets are scattered on the surface of the earth and embedded in trees in the act of vermin, game and clay target shooting for both pleasure and vermin control purposes. It is now recognised that where this falls on wetlands it may be accidentally ingested by wildfowl together with their normal grit diet deliberately consumed as an essential part of their gizzard digestive process. The outcome is that the lead is ground up by the gizzard resulting in poisoning, debilitation and death. A further problem now recognised is that lead shot deposited on land where crops are grown can be dissolved and enter into the structure of the crop which is designed for human consumption. The resulting concentration of lead can exceed the maximum permitted in foodstuffs by food regulations in all parts of the world.

A similar problem to wildfowl poisoning caused by the lead based weights used by fishermen has been resolved by the adoption of alternative heavy material for the weights. Attempts to apply a similar solution to the lead shot used in shotgun cartridges have proved much more difficult because of the stringent requirements imposed by the need for effective ballistics, safe performance and the economics related to the precious nature of many heavy metals. A shotgun shot must have the correct physical properties that allow it to provide correct ballistics and yet allow it to pass safely through a shotgun barrel at very high pressure without risking safety related to the proof of the gun.

One key property of lead that makes it so successful as a projectile material is its high density, 11.35 tonnes per m³, because the energy associated with the projectile at the moment it strikes the target relates to its mass and velocity as E = 1/2 mv². A second property of lead is its softness allowing it to pass through a gun barrel safely and without causing damage to the barrel structure despite high pressure and velocity. A third property is the ability of lead spheres to flatten slightly and retain the flattened shape thereby showing no elastic tendency. This enables the energy contained within the mass of the sphere to be transferred to the target with maximum lethal effect. A fourth property of lead is the relatively low melting point and ability to form alloys at low temperatures that will easily form spheres in simple manufacturing processes.

Lead has a modest position in the list of abundances of the metallic elements at 10 parts per million and poses no problem of dwindling resource.

Iron has been proposed as an alternative and has found some use but its density is only 7.86 tonnes per m³ which means it only carries 69.25% of the striking energy provided by lead projectiles of the same size. Iron shot also offers problems because of its hardness and rigidity, which could cause damage to the steel gun barrel bores of the modern shotgun, and is totally unusable in older shotguns with softer and thinner barrels. Iron shot also has a tendency to create abnormally high and dangerous pressures within the gun barrel bore as it passes through the conical, constrictive part of the bore known as the choke. Iron based shot has a tendency to corrode so that the individual shot spheres bind together producing a dangerous solid slug which can destroy the gun barrel. Iron based shot can become embedded in growing timber and pose a threat to timber processing machinery and this also stains oak timber and veneer because of the inter-reaction of steel with tannic acids in the oak to form inks. Some large timber producing countries have banned the use of steel shot in woodlands because of these problems. Iron based shot has considerable elasticity resulting in shot that ricochets dangerously and does not transmit its energy to the target in an effective and lethal manner resulting in wounding of live targets .

Tungsten has been proposed as an alternative and has found some use in alloys with steel and as a filler in powder form in various plastic polymers on its own or together with molybdenum. Tungsten has a density of 19.3 tonnes per m³ but it is so hard and unworkable, with a melting point of 3422°C, that it can only be contemplated for use if it is alloyed or softened by mixing with polymers. Even after such methods are applied the resulting shot has been found to be abrasive and sometimes to shatter or stick together causing damage to gun barrels and danger to the shooter. Examples of this technology are found in GB-A- 2200976 and WO94/24511.

Bismuth has also been proposed as an alternative and has found some use. The density is 9.747 tonnes per m³ and is approaching lead but its abundance is only 0.004 parts per million and it is a secondary metallurgical material, being a by-product of the refining of other metals. The price is high and the source precarious which means any attempt to adopt it generally would result in prohibitive price escalation. Bismuth is a very brittle metal and can only be made more usable if it is alloyed with tin or toxic lead. There have been alloys of bismuth and tin with the bismuth being the predominant component (EP 0478608) and alloys of bismuth and tin with the tin being the predominant component (GB 2327113 A) . The high bismuth alloys are expensive and rather brittle and the low bismuth alloys have a low density but are cheaper. Both are difficult to form into spheres with ease and both have resulting hardnesses of the shot far from ideal for optimum ballistic performance. Experiments conducted by the applicants suggest that, apart from density, the deformability of the shot material is also important. That is to say, that experiments suggest that both (a) resilience, i.e. recoverable deformability. and (b) the ability to deform permanently on striking the target, are important. Thus, shot which is substantially rigid tends to lack "stopping power" for shooting game, in that such shot tends to pass through the game or deflect at an obtuse or acute (ricochet) angle with significantly less transfer of energy to the game (as the shot retains the energy) than would corresponding lead shot and thus tends to wound, rather than kill, the game. On the other hand, shot which too readily undergoes a permanent deformation, produces too open a pattern at typical target distances. The applicants hypothesise that this is due to such shot becoming flattened by the acceleration imparted to it when the gun is fired, together with the compression of inertia, so that the individual pellets are no longer spherical and are deflected slightly, and randomly, by aerodynamic forces. Furthermore, shot which is too readily flattened on striking a target again tends to wound, rather than kill, game because penetration is insufficient since, presumably, too much energy has been lost by excessive flattening of the shot and/or such energy has been spread over a larger frontal area of the target.

It is an object of the present invention to provide an improved alternative shot material without the disadvantages of toxicity, elasticity, brittleness and high price whilst possessing the qualities of high enough density to carry energy effectively, softness and an ability to transmit to target the striking energy resulting in effective lethality. It is a further object of the present invention to provide an alloy of bismuth and tin that is modified to enable the resulting shot to be (a) manufactured easily using established techniques and (b) used in any shotgun of any calibre without the risk of barrel damage. It is a further object of the invention to provide an alloy from which conventional bullet projectiles for rifles, pistols and other guns with or without rifled barrels may be made.

According to a first aspect of the invention there is provided a shotgun shot, a pellet or a bullet, made of an alloy containing bismuth, tin and 2% to 5% by weight copper.

The alloy may contain more than 50% by weight bismuth but preferably it contains less than 50% by weight bismuth. In a preferred embodiment the alloy contains 45% by weight bismuth, 52% by weight tin and 3% by weight copper.

According to a second aspect the invention provides a method of manufacturing shotgun shot, pellets or bullets, comprising the steps of producing an alloy in accordance with the foregoing first aspect of the invention and forming the alloy into shot, pellets or bullets.

In a preferred method, because of the properties of the alloy, shot or pellets are formed by short or long drop forming. By this manner of forming, spherical shot or pellets can be easily produced having the desired physical properties of hardness, elasticity and malleability for optimum lethal effects upon striking of the target, whilst allowing them to pass safely through shotgun barrels having standard chokes .

As an alternative to drop forming, the alloy may be formed into a wire or strand which is cut into pieces and then swaged into shot, pellets or bullets. A further possibility is to form the shot, pellets or bullets by die- casting the molten alloy. Bullets may be formed from the alloy in conventional bullet moulds for ammunition for pistols, rifles and other weapons for sporting and military use.

According to a third aspect of the invention a shotgun cartridge is provided which includes a propellant charge and a quantity of shot in accordance with the foregoing first aspect of the invention.

According to a fourth aspect of the invention a pistol or rifle cartridge is provided which includes a propellant charge and a bullet in accordance with the foregoing first aspect of the invention.

In one embodiment of the invention the alloy is made by heating bismuth metal above its melting point of 271°C and adding tin, the melting point of which is 232°C, whilst continuing to heat the mixture. The melting point of the mixture is lower than either of the components when the ratio is around 45% bismuth and 55% tin. To the molten mixture copper is added at between 2% and 5% of the resulting total and the resulting molten alloy is mixed to ensure an homogenous blend. The resulting alloy has an ideal hardness for shot for shotgun cartridges and a density that is capable for transmitting sufficient energy in shot pellets of the standard sizes used for shotgun cartridges over the standard ranges expected by shotgun shooters. The density of the alloy is around 8.35 tonnes per m³, 73.57% of that of lead, and the hardness is similar to lead shot alloys containing 5% of antimony. Shot made from the alloy will flatten and retain the flattened shape in a very similar way to a 4% to 5% antimonial lead alloy shot. Bullets made from the alloy will perform in a similar way to antimonial lead bullets and bullets containing lead and copper.

EXAMPLE A 99.9999% pure grade of elemental bismuth is melted in a conventional metallurgical melting vessel with a stirrer and to it is added a 99.9999% pure grade of elemental tin so that the resultant, molten mixture contains 45% bismuth by weight of the final total and 50% tin by weight of the final total. After stirring to achieve a well mixed alloy, 5% by weight of the final total of 99.9999% pure grade copper is added with sufficient heating and stirring to achieve a molten and homogenous alloy.

The resulting alloy is cast into moulds to form ingots for use in a short drop shot casting machine or a conventional gun bullet casting machine or mould.

The pellets can be cast into spherical shot with sizes from 2mm diameter to 3.5mm diameter. The bullets can be cast into all calibre sizes.

It has been found that the shot formed has excellent ballistic performance in tests in the field superior to that of simple bismuth/tin alloys, despite the fact that the density is lower than some of the simpler alloys. It has also been found that the manufacturing process is greatly simplified by the modification of the alloy. Bullets made from the alloy have a ballistic performance very similar to copper coated lead bullets .

The pellets manufactured as described in the example may be incorporated in a shotgun cartridge in which the propellant is retained within a casing by a wad made of fibre or plastics above which a number of near spherical shot pellets are situated, the pellets being retained by crimping the extremity o the casing or by some other readily releasable closure means, such as a further wad for example in the form of a cardboard or plastics disc. The bullets manufactured as described in the example may be incorporated in a pistol or rifle cartridge in which the propellant is retained within a casing made of brass or other metals or metal alloys and the bullets are retained by crimping the extremity of the case.

Claims

1. A shotgun shot, a pellet or a bullet, made of an alloy containing bismuth and tin, and characterised by the inclusion of 2% to 5% by weight copper.

2. A shotgun shot, pellet or bullet according to claim 1 charactersied in that the alloy contains less than 50% by weight bismuth.

3. A shotgun shot, pellet or bullet according to claim 1 characterised in that the alloy contains by weight 45% bismuth, 52% tin and 3% copper.

4. A shotgun shot, pellet or bullet according to claim 1 characterised in that the alloy contains by weight 45% bismuth, 50% tin and 5% copper, the bismuth and copper being 99.999% pure grade.

5. A method of manufacturing shotgun shot, pellets or bullets, characterised in that it comprises the steps of producing an alloy as provided in any preceding claim and forming the alloy into shot, pellets or bullets.

6. A method according to claim 5 characterised in that the shot or pellets are formed by short drop forming.

7. A method according to claim 5 characterised in that the shot or pellets are formed by long drop forming.

8. A method according to claim 5 characterised in that the alloy is formed into a wire or strand which is cut into pieces and then swaged into shot, pellets or bullets.

9. A method according to claim 5 characterised in that the shot, pellets or bullets are formed by die-casting the molten alloy.

10. A method according to claim 5 characterised in that the pellets are cast into spherical shot of a diameter of 2mm to 3.5mm.

11. A method according to claim 5 characterised in that the bullets are formed from the alloy in bullet moulds.

12. A shotgun cartridge including a propellant charge and characterised in that it includes a quantity of shot in accordance with any of claims 1 to 4.

13. A pistol or rifle cartridge including a propellant charge and a bullet, characterised in that the bullet is made of an alloy in accordance with any of claims 1 to 4.