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The shaft is the primary structural element of the arrow, to which the other components are attached. The stiffness of the shaft is known as its spine, referring to how little the shaft bends when compressed. Hence, an arrow which bends less is said to have more spine.
Choosing your arrow is a two-part process:
Firstly - decide on what arrow weight you are wanting to shoot, this will in help determine what type of shaft yow will need.
Secondly - choose the correct spine to complement your draw weight and the arrow length.
How to determine weight and speed goals:
Not all bowhunters need to shoot the fastest and lightest of arrows (shooting feather-weights can damage your bow including accessories attached). Light arrows don't absorb up as much of the bow's energy as heavier arrows which in turn leaves more energy behind that has to be dissipated through vibration.
If the arrows you are using are too light, your bow can literally be shaken to pieces. The Archery Manufacturer's Organization (AMO) has proposed a standard minimum arrow weight of roughly 6 grains for each pound of your bow's maximum draw weight (66 pound bow = 390 grain arrow).
Today, a heavy hunting arrow could weigh 8 to 10 grains per pound. If you really want to go for speed, the standard of 5 grains per pound set by the International Bowhunter's Organization (IBO) for its endorsed 3-D tournaments is as light as you should go.
Hunting with Ultra-light arrows:
If you want to push things to the limit for the flattest possible trajectory, shoot arrows weighing 5 grains per pound of draw force. Two shaft choices exist:
1) The same thin-walled aluminium arrows listed above cut down for an overdraw
2) Full-length composite shafts made of aluminium and carbon (Easton ACC's) and the current selection of internal component carbon shafts such as the Beman ICS Hunter, Easton Evolution, Gold Tip and Carbon Express among others.
Hunting with Mid-weight arrows:
Arrows weighing between 6 and 8 grains per pound offer a good compromise between quiet shooting, long-term durability and flat trajectory. Consider any of the following three options:
1) The arrow sizes listed above cut down for an overdraw
2) Full-length thin-walled aluminium shafts such as 2212, 2213, 2312, 2413, 2512 and 2613 3) All-carbon shafts
Hunting with Heavy-weight arrows:
Arrows weighing 8 to 10 grains per pound of peak draw force will make your bow fairly silent while soaking up a little extra penetration energy. These weights correspond with full-length aluminium arrows having medium thickness walls such as the 2115, 2215, 2315, 2314, 2216, 2317 and 2514.
Correct shaft stiffness (or spine):
Arrows released with fingers perform differently from those released with a mechanical aid. A finger-released arrow must go through a series of side-to-side oscillations called "paradox" which is started when the string moves laterally to clear your fingers. The bending of the shaft must be timed perfectly so that it passes cleanly around the bow without hitting the riser or rest. To achieve good flight, your arrow shafts have to be an exact match for your bow and your release style.
A arrow released with a mechanical aid flexes much less as it leaves the bow. The flex that does occur is generally confined to the vertical plane (up and down). When using a release aid, you can get away with a wider range of shaft stiffness and still enjoy good arrow flight (to be on the safe side, it is best to stick with the recommendations of the shaft selection chart put together by each arrow manufacturer).
Because factors other than release style have a bearing on shaft stiffness, (such as whether or not you shoot an overdraw, string material, bow style and letoff) you will have to work out a "calculated" bow weight for use with these charts. If you request a brochure from an arrow manufacturer, it will have this step-by-step calculation spelled out for you. Make sure to work through it before referring to the shaft selection chart.
The point weight:
Point weight is also an important aspect of choosing the correct arrow stiffness, especially if you release with fingers. Determine what broadhead weight you will be hunting with before choosing your arrows, and then use field points of the same weight for off-season practice.
Price vs. straightness:
Most arrows are manufactured in grades. This is little more than a marketing ploy – a way to partition the market in order to charge more money for the high-grade product. In most cases, there is only one difference that separates the categories straightness:
- Top grade arrows have straightness tolerances of +/- .001 to +/- .002 inch.
- Lower grade arrows have straightness tolerances of +/- .003 to +/- .006 inch.
In most typical hunting distances there is no difference in accuracy between the various shaft grades. Unless you’re buying additional features (like better nock systems or a camo finish) there’s no reason to spend extra for arrows that are only a few thousandths of an inch straighter. You won’t notice the difference
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