Written by: Kim Lockhart, Copyright.
Modern Hunting Crossbows:
Modern hunting crossbows are of the recurve or compound archery bow design that shoot arrows that are the same as any hand-held bow's arrow. Crossbows are a variation on the general bow design. Instead of the limbs being hand-held vertically, they are mounted horizontally on a stock much like that of a rifle.
The limb design can either be recurve or compound with several different stock design features, but the basic concept of firing is the same. The string is pulled back locked into place. The string remains in this locked position, held soley through mechanical means until the energy stored in its limbs is released by a trigger mechanism, which launches the arrow. Crossbows have a much shorter draw length than bows. This means that for the same energy to be imparted to the arrow crossbows have a much higher Draw Weight and will usually require some kind of cocking apperatus to overcome the extra resistance of much stronger bow limbs.
Recurve crossbows are really quite simple in design. They consist of a stock, a simple prod, a metal, wood or fiberglas laminate limb which bends to store energy and is released with a trigger device releasing this stored energy to launch the arrow. Recurve crossbows are a bow that has tips curving away from the archer. The recurve crossbow's bent limbs have a longer draw length than an equivalent straight-limbed crossbow, giving more acceleration to the arrow.
Recurve crossbows have been around for thousands of years, they date as far back as 341 BC. Since that time they've evolved substantially in design, have become lighter in weight, and are more accurate as well. An inherit feature of recurve crossbows is; they are somewhat quieter when fired as opposed to a much faster compound crossbow.
Cocking any crossbow off center is the # 1 cause of accuracy problems, and recurve crossbows are the most sensitive to this issue. The recurve crossbows limbs have no way to adjust to uneven pressure when cocking.
Two factors determine the energy recurve crossbows can hold.
1. Its draw weight, which is the amount of force required to draw the recurve bow. A recurve crossbow's draw weight increases the farther back you pull the string until it reaches its peak weight, with no let off.
2. Its draw length is the distance between the crossbowstring's position at rest and its position when drawn.
Crossbow manufacturers express this power in terms of:
1. The crossbow's peak draw weight.
2. The crossbow's energy, measured in foot-pounds.
3. The crossbow arrow's velocity, measured in feet per second.
Compound crossbow have a string attached to pulleys, one or both of which has one or more cables attached to the opposite limb. When the string is drawn back, the string causes the pulleys to turn. This causes the pulleys to pull the cables, which in turn causes the limbs to bend and thus store energy. Compound crossbows, the string is held back mechanically and released by a trigger mechanism mounted internally.
A compound crossbow's central mount for the limbs, is called the riser. Risers are designed to be as rigid as possible. The central riser of a compound crossbow is usually made of aluminium or magnesium, and many are made of the aircraft-grade aluminium alloy.
Compound crossbow limbs are made of composite materials and are capable of taking high tensile and compressive forces. The limbs store all the energy of the crossbow, no energy is stored in the pulleys and cables. The limbs of a compound crossbow are usually much stiffer than those of a recurve crossbow. This limb stiffness makes the compound crossbow more energy efficient than other crossbows, but the limbs are too stiff to be drawn comfortably with a string attached directly to them.
The compound crossbow has the string attached to the pulleys, one or both of which has one or more cables attached to the opposite limb. When the string is drawn back, the string causes the pulleys to turn. This causes the pulleys to pull the cables, which in turn causes the limbs to bend and thus store energy. Compound crossbows generally use only pulleys that are both round and concentrically mounted, in order to capture the maximum available energy from the relatively short draw length.
When cams are used, this unique feature in design allows more arrow velocity in a given draw distance or (powerstroke) as opposed to a recurve crossbow of the same weight pull. Arrow peeds are not only derived from the draw weight of the crossbow. The longer the power stroke, the faster the arrow will travel. This in conjunction with weight and harness assembly, i.e. high energy cams, and synthetic cables and string store more energy than a heavier weight crossbow with a shorter power stroke.
The compound crossbow is little-affected by changes in temperature and humidity and it gives superior accuracy, velocity, and distance in comparison to other crossbows. Compound crossbows require slightly more effort to service because of wheels, cams, cables and strings, but are more compact in design, deliver more energy per inch of power stroke and are up to 15% more efficient.
Cocking is typically easier due to the shorter overall length as well as the built-in "let off" in draw weight, making it less critical to cock evenly due to the working characteristics of the wheels or cams.
A compound crossbow will "let-off" about 33% when the wheels roll over on most current compound crossbow models. Not only is it easier for the user to cock a compound crossbow, but also it is less mechanical stress on the trigger mechanism.
1. This first thing to know about crossbow sights, is understanding their function, which is, all crossbow sighting systems give you a point of aim on any target thus increasing the accuracy of the crossbow.
2. The second thing to know in crossbow sights, is that all crossbow sighting systems compensate arrow drop or the (arrows trajectory).
3. The third thing to know in crossbow sights, is that a arrow constantly drops once leaving the crossbow, the arc that it drops in, is the arrows trajectory.
Peep and Pin Sights:
The peep and pin sight is the most common crossbow sight and they are quite comparable to the sights found on most hand bows. The real advantage of these sights is in foul weather, rain, snow, there are no glass lenses to worry about keeping dry and clear. The disadvantage with this sight is if your eyes are having a hard time of focusing such as when you get older you can not get a sharp clear sight picture rendering this sight useless.
Telescopic Sights / Crossbow Scopes:
Telescopic sights consist of a tube and crosswire sight or crosshair mounted internally and the tube is mounted on the crossbow. Telescopic sights are magnified to make targets appear closer aiding in more precise shot placement within crossbow range.
Crossbow telescopic sights generally improves a crossbow hunters efforts in gaining the true accuracy potential of their crossbow by adding some magnification to the sight picture. With a scoped crossbow, sighting game is easier, quicker, and very precise simply because everything appears larger and closer do to magnification.
Crossbow hunters with less than perfect vision will find they are aided by the use of magnification usually 1 1/2x - 4x fixed power are good choices. A heavy duplex reticle is a good choice on crossbow scopes because they are much easier to see.
The crossbow scope should have it's parallax adjusted to around 35 - 50 yards as this is where most game animals within crossbow distance will be. A wide field of view is a good choice as this will aid in quicker target acquisition.
Note: When buying rings and or mounts for your crossbow be sure of the size of the clamp mount as to whether it is standard weaver or 3/8" dovetail such as a rimfire scope.
All Barnett crossbows and cheaper taiwan manufacture Barnett knock-offs use 3/8" dovetail mounting.
Note: Bushnell makes a good Rimfire Riflescope that the parallax is adjusted for 50 yards that is a 1" tube x 32mm for good light gathering capabilities and comes with the rings that will bolt right up to the Barnett crossbows for around $50.00.
Trajectory Compensating and Range Finding Reticle.
The trajectory / range-finding reticle is an excellent choice as well once you understand how simplistic this system is. Range-finding feature is simplistic as the average white-tailed deer is approximately 36" from brisket to rump, you simply move the scope up and down till the deer fits between the heavy stadia wires and you have the deer ranged then you simply select the crosshair that is that range hold dead on and shoot.
The dot sight really has an advantage in extremely low light conditions as the aiming point is illuminated, the disadvantage is in really bright light the dot can almost be rendered useless as the brightness washes out the lit sight. This type of sight has another disadvantage as well, the battery powering the sight might just go dead at the most critical time.
Trajectory Compensating Dot Sight.
The latest innovation from truglo for crossbow hunters is their holograghic dot sight that allows you to select your crossbow arrow speed to space the dots for trajectory compensation correctly at given yardages. Non-magnified, parallax corrected at 30 yards.