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Arrow weight, spine and straightness for crossbows
Weight keeps a crossbow safe, while spine and straightness decide how consistently the bolt flies once it leaves the rail.
Total weight and safety
Total finished weight is the safety figure. Meeting the maker's minimum, often 5 grains per pound of draw weight or a flat figure such as 400 grains, keeps the bow from behaving like a dry-fire and protects the limbs and warranty.
Above that floor, extra weight buys momentum. Heavier bolts fly a little slower but carry more energy into the target, which is why many hunters run heavier than the bare minimum for penetration.
What spine does
Spine is the shaft's stiffness, or how much it flexes under load. When the string drives the bolt, the shaft bends slightly and then recovers, and a spine matched to the bow's energy lets that flex settle quickly for a clean, repeatable launch.
Crossbow shafts are stiffer than most vertical-bow arrows because of the higher energy involved. Using the maker's recommended arrow keeps spine in the right range for the bow.
Straightness tolerances
Straightness is quoted as a tolerance such as.003 or.001 inch, describing how far the shaft may deviate from true along its length. A.001 shaft is held to a tighter tolerance than a.003 shaft, so it tends to fly more consistently arrow to arrow.
For close range the difference is small, but at longer distances a straighter shaft groups tighter, which is why premium hunting and target bolts advertise the tighter numbers.
Putting it together
For a safe, accurate setup, first clear the minimum total weight for your bow, then use a shaft with the spine the maker recommends and a straightness that suits your range. Consistency across a set of bolts, all built the same, matters as much as the numbers themselves.
The simplest way to stay in spec is to start from your crossbow model, which fixes length, nock and minimum weight, and choose a straightness grade from there.
Choose bolts that fit your bow
Open the bolt finder toolSelect your crossbow to see matching weight, spine and nock.Find TenPoint EVO-X CenterPunch bolts on eBayaffiliateRelated
Sources: Easton · TenPoint · Archery Trade Association