Middleton The Practical Guide to Man-powered Bullets

Experiments with Catapults, Musketballs, Stonebows, Blowpipes, Big Airguns and Bullet Bows
1. Auflage 2014
ISBN: 978-1-906122-78-2
Verlag: Merlin Unwin Books
Format: EPUB
Kopierschutz: 6 - ePub Watermark

E-Book, Englisch, 224 Seiten

This book explores in practical detail many of the ways, old and new, in which people can shoot bullets by their own force, without the aid of explosives. David slew Goliath with a stone from a sling, but it was a large stone and Man has long been shooting small stones and carefully rounded bullets of clay, glass - and latterly steel and lead - from a variety of weapons without recourse to gunpowder. The bow and arrow has been Man's choice for the last 10,000 years, when modern firearms have been unavailable or unsuitable. There is currently an explosion of interest in making primitive archery equipment. The author has been building bows and shooting flint-tipped arrows since adolescence. But the addiction has led to stronger stuff: to experiments with making and shooting pump-up airguns, stonebows and home-made lead musketballs. Richard Middleton's narrative is lively, humorous and full of exciting information and experimentation. In this quirky and clever book, he invites you to share the thrills of his garden shed experiments.  

Born in the colonies, educated in England, Richard Middleton is a member of the Society of Archer Antiquaries and now lives in the Colonies again. His wife, who edited out all the vainglorious bits of this biography (which is why it is now so short), has declined (refused point-blank) to have The Practical Guide to Man-Powered Bullets dedicated to her, and only wishes it recorded that she is a saint for putting up with all Richard's experimental weapon-making activities. Though Richard's interest always returns to the simple catapult, over the last 30 years he has made countless bows, crossbows, and even airguns to study the velocity and trajectory patterns of their missiles. He likes to test things for himself rather than to believe handed-down orthodoxies - an attitude not without its costs, some might add.

Autoren/Hrsg.

Middleton, Richard

Leseproben

Introduction

The function of a bullet is to impart a blow. The weapon is the interesting means by which a missile is sent on its way, but the work itself is done by the bullet.

Human-propelled bullets are low-velocity bullets, and low-velocity bullets require explanation but not apology. The justifications lie in the immutable laws of physics. Explaining physical laws is clearly something our schools fail to do, or young Bob’s flat tyres, as he labours to school past my house on his bike, would be pumped up of a morning.

One of the instruments for measuring projectile velocity – indeed the first, used by Benjamin Robins and Professor Hutton in the eighteenth century for musket balls and cannonballs respectively – is the ballistic pendulum. The bullet is shot at a heavy pendulum bob, and the momentum of the bob is calculated from observing how far it swings after the bullet has collided with it. It is a very easy instrument to make; for years I had a seven-foot pendulum of surprising accuracy, if I ever had the patience to gather a statistically valid sample of shots, hanging from the ceiling in my garage, with a bob weighing twelve pounds. Since I also had an electronic chronograph, I could and often did shoot different projectiles with known energy at this pendulum, and it was very noticeable that when struck by a .22 airgun pellet at 620 fps it swung about half an inch, whereas when struck by a .451 calibre lead ball from a catapult at 196 fps, it swung an inch and a half. The interesting fact is that both of these missiles have exactly 12 foot-pounds of energy.

This, then, is the first justification for the low-velocity bullet. Suppose, instead of a 12-pound pendulum bob I wanted to swing a 12-pound cat off my thyme bush, where it was performing such deeds as cats do perform on thyme bushes, I could move it an inch and a half with the slow catapult ball, but only half an inch with the airgun pellet. The example is rather unlikely owing to several obvious factors – the rarity of 12-pound cats being only one of them – but the principle is sound. If I were to want to move my cat the same distance with the airgun pellet, it would need a velocity of 1,964 fps which is the phenomenal energy of 120 foot-pounds. Ignoring the rude remark of my veterinary surgeon friend – that the cat would not move at all – we can see that the amount of energy required by a projectile to fetch a given clout to the target is inversely proportional to the weight of the bullet. For a given momentum, if the bullet is ten times as heavy, it needs a tenth of the energy to have the same effect on our 12-pound cat.

As a necessary digression, the removal of cats from gardens is better achieved with a larger, lighter missile having less momentum, penetration being highly undesirable for certain tasks. Discussing this with my shooting colleagues I received a letter from Dr. Lambie which is worth quoting in full:

The second reason we are drawn to slow bullets is that it always takes more energy to achieve high velocity, than it does to achieve the same momentum with a heavier bullet and a lower velocity. It is curious, but that is all, that I happened on the figures for a 12 foot-pound airgun and a 12 foot-pound catapult not by theoretical physics but by happy coincidence. I do shoot such pellets from an airgun, and I also have a .451 calibre spherical bullet mould, and in their respective weapons each does indeed produce 12 foot-pounds of energy. The airgun pellet is obliging enough to weigh exactly a tenth of the weight of the lead ball. This illustrates just how expensive high velocity is; with the same energy, the airgun pellet moves a little more than three times as fast as the heavy ball, yet the ball carries ten times the mass.

When we were testing his Borneo blowpipe, a friend and I found we could neither of us get any velocity higher than 203 fps, and that out of an 8-grain pellet. The best we managed with a 20-grain pellet was 176 fps, which was double the muzzle energy. (We had to use pellets because the long dart tripped the chronograph sensors at an angle and gave unreliable figures.) The Borneo darts weighed 26 grains, and we worked out that the Borneo tribesman, whose lungs were trained to the job, could have achieved 203 fps with these darts if he approached double our best energy input. But if he wanted the dart to go faster – say 300 fps – he would need to produce almost four times as much energy as we were able to. We are apt to forget that energy is required to shoot the bullet from our weapon; and it takes a great deal less energy to give a heavy ball a given momentum than it does a very light pellet. If the energy is limited to that which we supply with our muscles, this becomes quite significant. Fortunately for the tribesmen of Borneo, their darts rely on poison and not on muzzle energy.

The third attraction of the low-velocity bullet is reduced drag. Benjamin Robins found that the drag on a bullet is proportional to the square of its velocity up to a speed of about 800 fps. As it approaches the speed of sound, 1,080 fps, the drag rises dramatically, and creeps to somewhere around three times as much.

In 1901 Fremantle published the velocity of the .303 bullet measured at every 100 yards up to the range of 2,000 yards and from this data we can learn all manner of interesting things. The bullet weighed almost exactly half an ounce, being 215 grains, and this is highly convenient because a half-ounce (218.75 grains) lead ball is one of the best low-velocity bullets to use whether from a catapult or a crossbow. Fremantle’s table gives a great many details which do not concern us, but from his velocities it is easy to calculate how much energy is lost every 100 yards, this energy loss being the result of drag. At speeds above that of sound, the drag is about 17% every 100 yards, while below the speed of sound, it is only 7½% every 100 yards. That is to say, if the .303 bullet is going faster than 1,100 fps, 100 yards later it will have lost about 17% of its energy; while if it is going below 800 fps, after 100 yards it will only have lost 7½% of its energy.

Now this might lead us in the direction of very slow bullets indeed, but it is necessary to have a certain amount of speed or the target will up and stretch itself and leave the field before the arrival of the bullet. Besides, as we discover by the very practical means of building a series of low velocity bullet-shooting weapons, there is always an optimum weight; a weight of bullet which, if either exceeded or reduced, results in a less efficient transfer of energy. Imagine, for example, a fibreglass, recurve target bow with a 44-pound draw weight. Being no particular respecter of the products, admirable though they may be, of Mr. Yamaha, I altered such a bow to shoot bullets and got a one-ounce bullet to fly briskly at 182 fps, producing 32 foot-pounds. This, could I but shoot it accurately, might be a useful sort of thing to have. But it is hard to imagine the same weapon shooting a one-pound iron cannonball to any useful purpose. As a matter of fact, and as we shall see with all of these weapons, bullets have their greatest energy when they weigh somewhere around an ounce; a bit more with some weapons, a bit less with others.

But...