GB2327113A - Low toxicity shot pellets - Google Patents

Abstract

A shotgun shot or pellet, or a bullet, is made from a bismuth/tin alloy comprising less than 50% by weight bismuth, preferably the eutectic alloy of bismuth and tin, comprising approximately 45% bismuth and 55% tin.

Description

DESCRIPTION OF INVENTION Title: "Low Toxicity Shot Pellets" THIS INVENTION relates to shot pellets and the like.

Many thousands of tonnes of lead shotgun pellets are scattered on the surface of the earth and embedded in trees each year 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.

A similar problem of wildfowl poisoning caused by the lead weights used by fishermen has been resolved by the adoption of alternative heavy materials 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 shot material is its high density, 11.35 tonnes per m3, because the energy associated with the shot at the moment it strikes the target relates to its mass and its 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.

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 or steel 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 shot of the same size. Iron shot also offers problems because of its hardness and rigidity, which causes damage to the steel gun barrel bores of the modern shotgun, and has a tendency to create abnormally high and dangerous pressures. 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 poses a dangerous threat to timber processing machinery. It has also been found that such embedded shot damages the machinery and stains the timber resulting in devaluation of the timber. Some countries have imposed a ban on the use of iron shot as a result. The elasticity of iron and steel results 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.

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. However, bismuth is a very brittle metal. It has been proposed to manufacture shotgun shot from an alloy of bismuth with tin, in which bismuth predominates, but whilst the density of such shot is relatively high, an alloy in which bismuth predominates is still excessively hard and is difficult to work.

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 (at least in the short term) 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 with significantly less transfer of energy to the game than would corresponding lead shot and thus tends to wound, rather than kill, the game. On the other hand, shot which is too readily deformable, and, in particular, which too readily undergoes a permanent deformation, produces too open a pattern at typical target distances. The applicants hypothesize that this is due to such shot becoming flattened by the acceleration imparted to it when the gun is fired, so that the individual shot 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 density, malleability and an ability to transmit to targets the striking energy resulting in effective lethality.

According to one aspect of the invention there is provided a shotgun shot or pellet or a bullet, made from an alloy including bismuth and tin and comprising less than 50% by weight bismuth.

Preferably the alloy is a eutectic alloy of bismuth and tin.

According to a further aspect of the invention there is provided a method of manufacturing shotgun shot or pellets or bullets, comprising forming an alloy including bismuth and tin and incorporating less than 50% by weight bismuth and forming said alloy into shot, pellets or bullets.

The applicants have discovered that, in particular, an alloy comprising approximately 45% bismuth and 55% tin and which has a density significantly greater than that of iron, has excellent malleability and can be made into shot which is far superior to steel shot from a ballistic viewpoint in addition to being far less prone to damaging gun barrels, or to shatter or ricochet. The alloy is soft enough to make it unnecessary to use special protective wads for shot made from such alloy to prevent damage to gun barrels. Such protective wads are, of course, necessary with steel shot. Such special protective wads are difficult to manufacture as environmentally acceptable components and the fact that they are not required with shot in accordance with the present invention enables cartridges incorporating shot in accordance with the invention to be made using a higher proportion of environmentally acceptable, (e.g. biodegradable) components than cartridges incorporating steel shot. The eutectic bismuth/tin alloy, furthermore, is easily worked, making for ease of manufacture of such shot.

Various techniques may be used for forming the alloy into shot, pellets or bullets.

The alloy may be formed, for example, by extrusion casting or by drawing into a strand or wire which is cut into pieces which are thereafter swaged into shot or pellets.

As another possibility, the shot, pellets or bullets may be formed by die casting the molten alloy. As a further possibility, shot or pellets may be formed by short drop forming, i.e. a technique in which molten alloy is passed through a sieve or mesh to break it into a plurality of droplets and the droplets allowed to fall into a coolant liquid just below the sieve where they solidify as balls.

Whilst the preferred alloy of bismuth and tin in accordance with the present invention is somewhat less dense than pure bismuth, (having an S.G. of 8.23 as opposed to 9.747 for pure bismuth), the other physical properties of the alloy are superior to those of pure bismuth, for the purpose concerned, and are likewise superior to those of an alloy comprising in excess of 90% bismuth, which has been proposed for shot. Thus, the eutectic alloy is softer and more malleable than bismuth, (which is, as noted above, brittle, so that pure bismuth shot tend to shatter when fired from a gun) and is likewise more malleable and less shatter prone than such high-bismuth alloy. This affects both the range and the spread of the shot, since the shot fragments resulting from shattering do not carry as far as whole shot and are more prone to be deflected by aerodynamic forces than the substantially spherical whole shot. Shattering of shot furthermore tends to spoil game meat, insofar as minute fragments of shot are not readily detectable in preparing game for the table.

The preferred alloy, is, coincidentally, the eutectic alloy of bismuth and tin, which makes manufacture of shot, etc. from such alloy by moulding, casting or dropping the molten alloy a straightforward matter, particularly since the melting point of such alloy is conveniently low. Such eutectic alloy comprises substantially 45% by weight bismuth and 55% by weight tin.

In view of the malleability of the alloy, it is easy to work the alloy, in the cold state into desired shapes, e.g. into spherical shot or pellets. By contrast, pure bismuth, and the high-bismuth alloy referred to above are difficult to form. The melting point of the eutectic alloy is even lower, at around 1600C, than that of pure bismuth (271.30C) facilitating manufacture of shot, pellets or bullets by moulding, casting or dropping.

A further method of manufacture which may be adopted is to form the alloy into a wire or strand, and thereafter to pass the strand between cooperating steel rollers each having hemi-spherical dimples at regular intervals around its periphery, the rollers being driven in synchronism so that, as the rollers rotate, each dimple in one roller comes, in turn, into register with the complementary dimple in the other roller, whereby the strand is deformed into a thin, flat tape with substantially spherical nodules at intervals therealong, each nodule having an equatorial plane corresponding to the plane of the tape, the spherical nodules being thereafter punched from the tape, or otherwise separated from the tape, to form shot. Indeed, the peripheral surfaces of the cooperating rollers may be formed to provide cutting edges around the dimples so that the rollers both form the shot and punch the shot from the "tape" scrap. It will be understood that, by reason of the low melting point of the alloy, recycling of the scrap to the appropriate preceding stage in the process can be carried out in a very straightforward manner in the same production line with the minimum of handling.

Claims (8)

1. A shotgun shot or pellet, or a bullet, made from an alloy including bismuth and tin and comprising less than 50% by weight bismuth.

2. A shotgun shot or pellet, or a bullet, made from a eutectic alloy of bismuth and tin.

3. A shotgun shot or pellet, or a bullet, according to claim 1 wherein said alloy comprises bismuth, tin and a minor proportion of zinc.

4. A method of manufacturing shotgun shot or pellets, or bullets, comprising forming an alloy including bismuth and tin and incorporating less than 50% by weight bismuth, and forming said alloy into shot, pellets or bullets.

5. A method according to claim 4 wherein the alloy is formed into a strand or wire which is cut into pieces which are thereafter swaged into shot or pellets.

6. A method according to claim 4 wherein said shot, pellets or bullets are formed by die-casting the molten alloy.

7. A method according to claim 4, wherein said shot or pellets are formed by short drop forming.

8. A method of making shotgun shot or pellets, or bullets, substantially as hereinbefore described.

8. A shotgun cartridge including a propellant charge and a quantity of shot in accordance with any of claims 1 to 7.

9. Shotgun shot or pellets, or a bullet, substantially as hereinbefore described.

10. A method of making shotgun shot or pellets, or bullets, substantially as hereinbefore described.

11. Any novel feature or combination of features disclosed herein.

Amendments to the claims have been filed as follows 1. A shotgun shot or pellet, or a bullet, made from a eutectic alloy of bismuth and tin comprising 45% bismuth and 55% tin.

2. A method of manufacturing shotgun shot or pellets, or bullets, comprising forming an alloy made from a eutectic alloy of bismuth and tin and incorporating 45% bismuth and 55% tin, and forming said alloy into shot, pellets or bullets.

3. A method according to claim 2 wherein the alloy is formed into a strand or wire which is cut into pieces which are thereafter swaged into shot or pellets.

4. A method according to claim 2 wherein said shot, pellets or bullets are formed by die-casting the molten alloy.

5. A method according to claim 2, wherein said shot or pellets are formed by short drop forming.

6. A shotgun cartridge including a propellant charge and a quantity of shot in accordance with any of claims 1 to 5.

7. Shotgun shot or pellets, or a bullet, substantially as hereinbefore described.