If it was new attitudes and scientific research that brought about big changes in Archery in the first half of the 20th Century, it was one man’s creative genius that brought about the biggest innovation in the second half. The Compound Bow is a much better device at projecting arrows at high speed and great consistency and accuracy than anything that went before, even including Ballistas and Crossbows which come close, but are slower to deploy. Compound Bows are shot in the same basic way as Longbows and Recurves – held in one hand, and the string drawn back by the other hand / arm – but have these radical advantages:
- The maximimum draw weight of the bow occurs near the beginning of the draw action, and the ‘holding weight’ is much less, making it easier to aim with precision, and also providing much better acceleration to the arrow.
- The archer can use a trigger-device called a release aid which has much less adverse effect on arrow flight than fingers and a tab.
- The archer can use a magnifying lens and a back-sight consisting of a peep-hole in the string to get much better alignment on the target.
The first of these advantages is due to the bow design, the other two apply if the Archer opts to shoot in the ‘Unlimited’ Style.
The main disadvantages of Compound Bows is that they are much more complex, with several moving parts, and they tend to have a heavier dead-weight in the bow hand, which is made worse because of the low holding-weight, there’s nothing to push against!
Compound Bows are fully recognised by ArcheryGB and World Archery in all disciplines except the Olympics, however they cannot be used in direct competition with recurves and other bow types as they have a clear advantage.
Simple Bows, like Longbows and Recurves, shoot arrows faster if their draw weight is greater, and they are easier to draw if their limbs are longer. Shorter bows of the same weight shoot arrows faster, which is something hunters try to achieve, but are increasingly difficult to control as the limbs are made shorter. In the 1950s and 60s most hunters used heavy-draw bows, either American Longbows (Flatbows) or short powerful recurve bows. The short bows were more handy in the woods but ‘critical’ in use, what was needed was a short fast bow that was easier to draw for the same high arrow speed. The Compound Bow was invented in 1966 when an engineer and archer called Hollness Wilbur Allen experimented with pulley systems giving a mechanical advantage so that the archer could draw a heavy weight by moving a smaller force over a greater distance – he started by cutting-down a conventional recurve bow. The early bows had four round pulleys, two attached to the ends of the limbs and the other two attached to the bow riser or the limb base. Because the bow limbs were short they only had to move a short distance to provide the draw weight, but the string moved further, and all compound bows form an acute string angle like Asiatic Bows. The next generation had two double pulleys rather than four single ones, all at the limb tips, and the big breakthrough was introduction of eccentric pulleys which meant that the leverage increased as the pulleys turned and ‘wobbled’ around its axle, so that the ‘hold-weight’ is less than the initial ‘peak weight’ at the start of the draw, the amount of weight reduction being called ‘let-off’. Allen’s 1969 Patent included double-pulleys and use of either eccentric round wheels or cam-shaped non circular profile pulleys.
The evolution of the mainstream compound bow (ignoring less conventional variations using linked / rocking recurve limbs) was from straight limbs with small wheels to curved limbs and then recurve limbs, still with round eccentric pulleys, and then to the use of cams with a variety of profiles to control ‘let-off’ and ‘valley’, leading to larger, and often asymmetrical, cams and smaller limbs, and then a trend towards extreme ‘deflex’ of the limbs so that they are nearly parallel at the top and bottom of the bow.
Hunting with bows is big business in the United States, where it’s estimated 18 million people participate. A very large number of these use Compound Bows, and for many years there’s been a kind of Arms Race to produce ever faster arrow speeds, although development has got to a point of diminishing returns as the fastest bow speeds get closer and closer to what seems to be the limit for human-powered projectiles, somewhere around 400 feet / 120 metres per second. There have been literally thousands of different models produced, the annual variations as each manufacturer rolls out their new model is often just a matter of a new Cam Profile and size, but over the years different riser designs and configurations, and materials, have come and gone and evolved.