mrmeval
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http://www.scienceinafrica.co.za/2004/april/airgun.htm
Sporting Air Rifles - a legal and environmental disaster
Garth Cambray
The pellet gun, a glorified pee shooter has gained popularity in South Africa in the last four or so years due to the modifications recently made to the Firearms Act, which allow such a weapon to be purchased without a licence.
An airgun is a quirky weapon. Even although it is classified as an airgun, most high powered pellet guns are actually firearms due to the explosion of oils in their chambers that may contribute up to 45% of total power. In this regard, the article argues that current legislation poses a threat to the environment and humans.
Air rifles are loosely divided into two categories, target rifles and sporting rifles. Target rifles have to propel a pellet from the shooter to the target in an accurate and efficient manner. They do not require incredible speed or power. Sporting air rifles on the other hand are constructed for purposes including, but not limited to, target practise and hence generally produce faster moving pellets which consequently have more power. This article deals with sporting air rifles.
In any object which expels a projectile the projectile is subject to the laws of gravity which causes a downward acceleration of the projectile. If the projectile is fired parallel to the ground, this effect causes the typical downward curved trajectory. The faster an object travels the flatter its trajectory is - if something travels a great distance in a short time gravity has little chance to act. Other factors such as atmospheric drag are also important. A lighter object will slow down faster than a heavier one, and hence a fast moving light object may initially have a flat trajectory, but as it slows, its trajectory will become more and more curved.
In a conventional firearm, a fast burning chemical mixture generates an increase in the gas volume in a closed area (the cartridge). This results in the cartridge separating into two pieces with the bullet driven down the barrel of the firearm and expelled at great velocity. The barrel can be rifled (i.e. it has a spiral groove carved into it) and this rifling causes the projectile to spin, increasing its accuracy. Such a firearm is called a rifle.
In an air rifle the projectile is supposedly driven down the rifling of the barrel by a source of gas other than that provided by a fast burning mixture. These gas sources range from bottled gas in a tank, to spring or compressed gas pistons. The next two types use a piston which is compressed by a lever. The piston is either driven by a spring or compressed air trapped behind it (a bit like the gas-lifts in some motor vehicles which hold the boot open.) And this is where it gets tricky.
In a diesel engine a fuel air mixture is injected into a cylinder where it is compressed by a piston. The compression action reaches a point at which the diesel fuel explodes and drives the piston through its cycle. In modern sporting air rifles the compression generated in the chamber of the air rifle is sufficient to cause small amounts of oil to combust with the compressed air oil mixture acting similarly to that of the fuel in a diesel engine. This causes at least a 45% increase in the exit velocity of the pellet from the rifle. This increase in velocity in turn allows an air-gun to approach muzzle velocities of close to, or above the speed of sound. At these speeds the power of a pellet may be four times that of a pellet travelling at half its speed.
A demonstration of this effect is simple for any air rifle enthusiast. Take your air gun and fire it at a target 50 times to clear up residual oil in the chamber. Sight the rifle so that it shoots on target at 20 metres. Mark where the pellets penetrate the target. Spray a small amount of light oil into the oiling points of the rifle, or even into the compression chamber (not recommended, but quite spectacular) and once again shoot another 20 shots at the target. The first few shots are spectacularly more powerful and shoot much higher on the target, and as the oil residues are used up, the power of the rifle decreases and the impact points approach those of the old pre-oiling impact points. You will also note with the first few shots you get a cloud of smoke, and if you do this at night you get a light orange muzzle flash.
In old fashioned air rifles muzzle velocities seldom exceeded 2/3 the speed of sound. Power was limited to that needed to make a hole in a cool drink can at 10 metres. If heavy pellets were used, this resulted in extremely slow moving projectiles which had a very rounded trajectory. Most pellets also began to tumble at 30-40m and hence rapidly dissipated energy. As a result, most people used very light pellets which had initial flat trajectories due to their reasonably high speed. These pellets had little inertia and hence were rapidly slowed down by the air and if they were able to make a hole in a tin can at 10 metres, were probably hardly able to make a dent in it at 30 metres.
The new breed of high power sport rifles on the other hand require using heavier pellets. Light pellets travelling at high velocities are subject to aerodynamic forces which cause them to become inaccurate and tumble. Heavier pellets however do not have these problems.
At this point we return to the diesel engine. The greater the compression of a diesel engine, the greater its power. This is what makes the difference between the diesel guzzling 40kw 1970's tractor engine and the race winning 200kw turbo-charged high compression diesel engines of today which use the same amount of fuel but have much greater power. If we look at a high powered air rifle with a heavy pellet the compression behind the pellet is enormous. If a large amount of oil is present in the compression chamber a powerful explosion occurs, which increases the power of that pellet gun to the point where more than 50% of its muzzle velocity is derived from fire, not air driven by a spring.
These high powered air rifles pose a serious threat to South Africa. As a responsible air rifle owner it is deeply disturbing that 15 year old would be able to purchase, with a helpful adult, a rifle which can kill a person, a cat, a dog, wild animals and can even maim things like cattle, donkeys, kudu in such a way that they will eventually die.
To put this into financial and scientific perspective. For an over 21 adult to purchase a firearm such as a .22 long rifle extensive applications would be made to the government, a minimum of R2000 would be spent on the rifle, a few hundred Rands would be spent on the licence and on a rifle users fitness test. The owner would also have to have a safe in their home (about R1000), which has to be inspected by the local police inspector. The rifle will fire ammunition which costs in the region of 30 cents per shot and this ammunition can kill for up to 2km. The owner also needs to sign a document which makes them personally liable for the death of somebody shot with their firearm if stolen from them under certain situations. Compare this procedure with that of obtaining a high powered sports rifle.
A 15 year old child would need between R700 and R2000 to buy a high powered sports rifle. He or she could order one from the back pages of a relevant magazine and it will be sent to a local shop for them to collect. Assuming the child's parents would not be willing to do this, a child could probably need to pay an additional R100 or so to get an adult to collect it for them. After that, they can buy ammunition by themselves. Pellets cost from 4.5-6.8 cents each. For R6, the cost of a cool drink, they can fire over 100 pellets. In some models, a heavy pellet will still have sufficient power to kill at 100m, break a window at 200m and blind somebody at 250m.
As a scientist, air rifle owner and environmentalist I believe that a level of control is needed over these new higher powered air rifles as they are dangerous weapons. In the hands of children they will cause a rapid decline in biodiversity with targets such as large birds and animals all being seen as fair game through the eyes of the youth. Due to the fact that they are indeed fire-arms deriving in excess of 45% of their maximum power from an explosion of a chemical mixture I propose that the laws controlling these more powerful models need to be reassessed, and that weaker 'children's models' be left as they are.
Sporting Air Rifles - a legal and environmental disaster
Garth Cambray
The pellet gun, a glorified pee shooter has gained popularity in South Africa in the last four or so years due to the modifications recently made to the Firearms Act, which allow such a weapon to be purchased without a licence.
An airgun is a quirky weapon. Even although it is classified as an airgun, most high powered pellet guns are actually firearms due to the explosion of oils in their chambers that may contribute up to 45% of total power. In this regard, the article argues that current legislation poses a threat to the environment and humans.
Air rifles are loosely divided into two categories, target rifles and sporting rifles. Target rifles have to propel a pellet from the shooter to the target in an accurate and efficient manner. They do not require incredible speed or power. Sporting air rifles on the other hand are constructed for purposes including, but not limited to, target practise and hence generally produce faster moving pellets which consequently have more power. This article deals with sporting air rifles.
In any object which expels a projectile the projectile is subject to the laws of gravity which causes a downward acceleration of the projectile. If the projectile is fired parallel to the ground, this effect causes the typical downward curved trajectory. The faster an object travels the flatter its trajectory is - if something travels a great distance in a short time gravity has little chance to act. Other factors such as atmospheric drag are also important. A lighter object will slow down faster than a heavier one, and hence a fast moving light object may initially have a flat trajectory, but as it slows, its trajectory will become more and more curved.
In a conventional firearm, a fast burning chemical mixture generates an increase in the gas volume in a closed area (the cartridge). This results in the cartridge separating into two pieces with the bullet driven down the barrel of the firearm and expelled at great velocity. The barrel can be rifled (i.e. it has a spiral groove carved into it) and this rifling causes the projectile to spin, increasing its accuracy. Such a firearm is called a rifle.
In an air rifle the projectile is supposedly driven down the rifling of the barrel by a source of gas other than that provided by a fast burning mixture. These gas sources range from bottled gas in a tank, to spring or compressed gas pistons. The next two types use a piston which is compressed by a lever. The piston is either driven by a spring or compressed air trapped behind it (a bit like the gas-lifts in some motor vehicles which hold the boot open.) And this is where it gets tricky.
In a diesel engine a fuel air mixture is injected into a cylinder where it is compressed by a piston. The compression action reaches a point at which the diesel fuel explodes and drives the piston through its cycle. In modern sporting air rifles the compression generated in the chamber of the air rifle is sufficient to cause small amounts of oil to combust with the compressed air oil mixture acting similarly to that of the fuel in a diesel engine. This causes at least a 45% increase in the exit velocity of the pellet from the rifle. This increase in velocity in turn allows an air-gun to approach muzzle velocities of close to, or above the speed of sound. At these speeds the power of a pellet may be four times that of a pellet travelling at half its speed.
A demonstration of this effect is simple for any air rifle enthusiast. Take your air gun and fire it at a target 50 times to clear up residual oil in the chamber. Sight the rifle so that it shoots on target at 20 metres. Mark where the pellets penetrate the target. Spray a small amount of light oil into the oiling points of the rifle, or even into the compression chamber (not recommended, but quite spectacular) and once again shoot another 20 shots at the target. The first few shots are spectacularly more powerful and shoot much higher on the target, and as the oil residues are used up, the power of the rifle decreases and the impact points approach those of the old pre-oiling impact points. You will also note with the first few shots you get a cloud of smoke, and if you do this at night you get a light orange muzzle flash.
In old fashioned air rifles muzzle velocities seldom exceeded 2/3 the speed of sound. Power was limited to that needed to make a hole in a cool drink can at 10 metres. If heavy pellets were used, this resulted in extremely slow moving projectiles which had a very rounded trajectory. Most pellets also began to tumble at 30-40m and hence rapidly dissipated energy. As a result, most people used very light pellets which had initial flat trajectories due to their reasonably high speed. These pellets had little inertia and hence were rapidly slowed down by the air and if they were able to make a hole in a tin can at 10 metres, were probably hardly able to make a dent in it at 30 metres.
The new breed of high power sport rifles on the other hand require using heavier pellets. Light pellets travelling at high velocities are subject to aerodynamic forces which cause them to become inaccurate and tumble. Heavier pellets however do not have these problems.
At this point we return to the diesel engine. The greater the compression of a diesel engine, the greater its power. This is what makes the difference between the diesel guzzling 40kw 1970's tractor engine and the race winning 200kw turbo-charged high compression diesel engines of today which use the same amount of fuel but have much greater power. If we look at a high powered air rifle with a heavy pellet the compression behind the pellet is enormous. If a large amount of oil is present in the compression chamber a powerful explosion occurs, which increases the power of that pellet gun to the point where more than 50% of its muzzle velocity is derived from fire, not air driven by a spring.
These high powered air rifles pose a serious threat to South Africa. As a responsible air rifle owner it is deeply disturbing that 15 year old would be able to purchase, with a helpful adult, a rifle which can kill a person, a cat, a dog, wild animals and can even maim things like cattle, donkeys, kudu in such a way that they will eventually die.
To put this into financial and scientific perspective. For an over 21 adult to purchase a firearm such as a .22 long rifle extensive applications would be made to the government, a minimum of R2000 would be spent on the rifle, a few hundred Rands would be spent on the licence and on a rifle users fitness test. The owner would also have to have a safe in their home (about R1000), which has to be inspected by the local police inspector. The rifle will fire ammunition which costs in the region of 30 cents per shot and this ammunition can kill for up to 2km. The owner also needs to sign a document which makes them personally liable for the death of somebody shot with their firearm if stolen from them under certain situations. Compare this procedure with that of obtaining a high powered sports rifle.
A 15 year old child would need between R700 and R2000 to buy a high powered sports rifle. He or she could order one from the back pages of a relevant magazine and it will be sent to a local shop for them to collect. Assuming the child's parents would not be willing to do this, a child could probably need to pay an additional R100 or so to get an adult to collect it for them. After that, they can buy ammunition by themselves. Pellets cost from 4.5-6.8 cents each. For R6, the cost of a cool drink, they can fire over 100 pellets. In some models, a heavy pellet will still have sufficient power to kill at 100m, break a window at 200m and blind somebody at 250m.
As a scientist, air rifle owner and environmentalist I believe that a level of control is needed over these new higher powered air rifles as they are dangerous weapons. In the hands of children they will cause a rapid decline in biodiversity with targets such as large birds and animals all being seen as fair game through the eyes of the youth. Due to the fact that they are indeed fire-arms deriving in excess of 45% of their maximum power from an explosion of a chemical mixture I propose that the laws controlling these more powerful models need to be reassessed, and that weaker 'children's models' be left as they are.
