One example is the TenPoint Alpha-Nock, which is designed specifically for narrow, high-speed crossbows. As crossbow technologies changed, the need to engineer a more efficient and safer nock came to the forefront. A nock is the initial point of contact for energy transfer from the string to the arrow. With the narrow, fast crossbows on the market today, nock design is more critical than ever. There have been flat, half-moon, and other U-shaped designs to increase safety and efficiency. 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. 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. Now add the weight of the nock, fletching, insert and point. 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. To figure out the weight of your arrow, multiply the arrow’s length times the gpi. Why is weight important? A lightweight arrow could cause the crossbow limbs to shatter with the ineffective transfer of energy.Īrrow weights are listed in grains per inch (gpi) of shaft. Always weigh an arrow as a complete package. The weight of the arrow needs to include the broadhead, nock, inserts and fletching. 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. 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. Most crossbow arrows are 20 or 22 inches long. The manufacturer will have checked the specifics to make sure it is safe. If all else fails, use the arrows packaged with your bow when you bought it. Choosing the incorrect arrow or nock can cause serious injury to the shooter and the crossbow. All crossbow manufacturers list a minimum arrow weight and length, and specify the type of nock. The three most important factors when selecting a crossbow arrow are the weight of the complete unit, length, and nock type. There are charts from arrow manufacturers to help determine the required stiffness of an arrow for the specific draw weights with a given bow. It is always a good lesson to video an arrow in flight with the slow-motion setting on a smartphone.Īlways refer to the crossbow manufacturer’s recommendations for spine. The flexing and bending of an arrow during flight can influence accuracy and consistency. 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 inside diameter, the cross-section shape and the thickness of the material all contribute to the arrow’s static spine. In multi-layered arrows, such as carbon and aluminum, the bonding materials of the layers also contribute to the stiffness. The factors that determine the spine’s forgiveness are the stiffness of the materials in the shaft and the geometry of the shaft. Arrows with high static spine will not bend as much as arrows with low static spine. The amount of bend at the center point determines the spine. 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. Static spine is simply the stiffness of the arrow and its resistance to bending. The energy released from the limbs to the string, and then transferred to the arrow, could cause the projectile to explode or shatter. Modern crossbows can shoot up to 470 fps, and shooting an arrow without enough spine from this bow could be disastrous. 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 have pushed the envelope for speed, accuracy and consistency, with most designs now pushing arrows well over 400 fps. Crossbows have been used for centuries, and the technological advancements through the years have made them efficient hunting tools.
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