Crossbows have been used for centuries, and the technological advancements through the years have made them efficient hunting tools. Modern crossbows have pushed the envelope for speed, accuracy and consistency, with most designs now pushing arrows well over 400 fps. To take advantage of the energy that modern bows generate, shooters need to pay close attention to the arrows they select, from front to back, to maximize the benefits or arrow flight and ensure safety.

Modern crossbows can shoot up to 470 fps, and shooting an arrow without enough spine from this bow could be disastrous. The energy released from the limbs to the string, and then transferred to the arrow, could cause the projectile to explode or shatter. Static spine is simply the stiffness of the arrow and its resistance to bending. To determine the level of the static spine in your arrow, support the arrow at two points, a known distance apart, and apply force in the center of the arrow in the form of weight. The amount of bend at the center point determines the spine. Arrows with high static spine will not bend as much as arrows with low static spine.

The factors that determine the spine’s forgiveness are the stiffness of the materials in the shaft and the geometry of the shaft. In multi-layered arrows, such as carbon and aluminum, the bonding materials of the layers also contribute to the stiffness. The inside diameter, the cross-section shape and the thickness of the material all contribute to the arrow’s static spine.

How much the arrow bends when fired is known as dynamic spine, which can be influenced by factors such as static spine, string force, fletching and nock weight. The flexing and bending of an arrow during flight can influence accuracy and consistency. It is always a good lesson to video an arrow in flight with the slow-motion setting on a smartphone.

Always refer to the crossbow manufacturer’s recommendations for spine. There are charts from arrow manufacturers to help determine the required stiffness of an arrow for the specific draw weights with a given bow.

The three most important factors when selecting a crossbow arrow are the weight of the complete unit, length, and nock type. All crossbow manufacturers list a minimum arrow weight and length, and specify the type of nock. Choosing the incorrect arrow or nock can cause serious injury to the shooter and the crossbow. If all else fails, use the arrows packaged with your bow when you bought it. The manufacturer will have checked the specifics to make sure it is safe.

Arrow Length

Most crossbow arrows are 20 or 22 inches long. Crossbow manufacturers specify a minimum length of the arrow for safety because shooting an arrow that’s too short will put the archer’s hand in the path of the string when loading an arrow on the rail. If you’re unsure what arrow length to use, refer to the owner’s manual for your crossbow or compare them to the arrows that came with your crossbow.

Arrow Weight

The weight of the arrow needs to include the broadhead, nock, inserts and fletching. Always weigh an arrow as a complete package. Why is weight important? A lightweight arrow could cause the crossbow limbs to shatter with the ineffective transfer of energy.

Arrow weights are listed in grains per inch (gpi) of shaft. To figure out the weight of your arrow, multiply the arrow’s length times the gpi. A 20-inch arrow that weighs 13 gpi would have a total weight determined with this calculation: 20 inches x 13 grains/inch = 260 grains. Now add the weight of the nock, fletching, insert and point. As an example, a nock is 15 grains, fletching 12 grains each for a total of 36 grains, an insert is 90 grains and a point is 100 grains: 260 + 15 + 36 + 90 + 100 = 501 grains.

Nock

There has been a myriad of nocks over the years to try and ensure string capture and maximize energy transfer from a crossbow to an arrow. There have been flat, half-moon, and other U-shaped designs to increase safety and efficiency. With the narrow, fast crossbows on the market today, nock design is more critical than ever. A nock is the initial point of contact for energy transfer from the string to the arrow. Failure is not an option. As crossbow technologies changed, the need to engineer a more efficient and safer nock came to the forefront.

One example is the TenPoint Alpha-Nock, which is designed specifically for narrow, high-speed crossbows. It employs a horseshoe shape, with a deep saddle that increases the string-to-nock engagement by 28 percent. The deep bowstring groove has a large smooth radius base, and elongated edges to ensure the string cannot jump over or under the arrow. With crossbow strings moving faster than ever, having it jump over or under the nock and arrow is a possibility.

The Alpha-Nock ensures the crossbow string consistently travels to the center of the nock, resulting in straight nock travel and increased downrange accuracy. They are also available in lighted options. Alpha-Brite, a three-piece lighted nock system works from an insert with a six-sided interior cavity designed to accept a combined LED unit and translucent pegged Alpha-Brite Nock. The nock receiver is glued into the nock-end of the arrow and indexed with the vanes. The new Alpha-Nocks can be used in any crossbow arrow with matching diameter.

Aluminum or Carbon?

Arrow manufacturers offer aluminum and carbon arrows in comparable lengths and weights. Aluminum shafts are more economical to manufacture but aren’t as popular as carbon alternatives. Carbon arrows flex and bend, which usually equates to a longer life span. One wrong bend or kink in aluminum and it will no longer be usable. Carbon shafts do not have memory and are straight, or they break. Carbon is more forgiving and tends to last longer if you don’t shoot something that will cause breakage.

Crossbow arrows are short when compared to those for vertical bows, and the energy transferred is mindboggling. Crossbow arrows decrease in speed quickly and lose energy over distance, which is part of archery of any kind. Shooting the lightest arrows possible can maximize range, but there’s a fine balance between weight, range and kinetic energy. A Full Metal Jacket (FMJ) arrow from Easton Archery can offer the best of both worlds, with a high-strength carbon core and aluminum outer shaft, it offers a weighted advantage, with less friction when the aluminum penetrates an animal. When you understand kinetic energy and penetration, the FMJ becomes a clear advantage.

All crossbow manufacturers have excellent recommendations to help you choose the right arrow. With a little time on the range experimenting with different arrow weights, materials and broadheads, you will quickly see where you gain or lose certain advantages to tweak your equipment and make informed decisions regarding what works best for you. Nothing beats field time with your crossbow to know and understand it and all its components. Get out and shoot.