True custom bolts have at least four important components: Static spine selection, spine indexing, extreme front-of-center (FOC) , and hand crafted with the most precise fletching available today.
Static spine matching is often confused with spine indexing. Spine matching is all about deflection, or the stiffness of the bolt. It is important to match the stiffness of the bolt to the poundage and draw stroke of the crossbow,that is why we use a selection of bolts including GT Laser II, Laser III, and Black Eagle executioner and different lengths. Just like with a vertical bow. Spine indexing is locating the weak spot on the bolt. Spine indexing is the most important accuracy factor in custom bolts. Extremely sensitive tooling is needed to accurately define low spine in a carbon shaft, and all carbon shafts have a low and high spine. Our research has shown that group shooting off of a shooting machine at 25 yards, with 6 bolts that have been spine indexed vs 6 bolts with factory fletching. The bolts that were spine indexed averaged a 68% tighter group.
The next precision element of Custom Bolts is that of front-of-center (FOC). The FOC refers to the balance point of a bolt. The percentage of FOC indicates what percent the balance point is forward of the center, the higher the percentage, the better performance your bolt will deliver. FOC has two benefits for precision minded archers. Archers can expect to see tighter groups with field tips and broadheads. The second advantage FOC creates is more momentum and less drag, thus deeper penetration on target! Borkholder Archery’s method of creating FOC is with a brass insert. Increasing the weight of your field tip will also create similar results. A benefit of using a brass insert is our ability to create a substantially larger amount of FOC than is possible with a field tip alone, while still using a 100 grain tip. This method is used on all of our custom bolts, which gives the consumer a larger selection of broad heads to choose from when ordering from us. We like to have 20% or more FOC This really comes into play at the longer yardages with marginal shot placement like the shoulder, having a brass insert or not could be the difference of your broad head stopping in the bone or getting into the vitals.
The final element of custom bolts is that of precision fletching. By using state of the art equipment and a highly trained expert creates the most accurate bolts available today. As a hunter, it is our responsibility to take quick, clean kills. The precision fletching jigs used on all of our custom bolts are within 1/72 of a degree of being spaced 120 degrees apart. It is very important that your vanes are spaced 120 deg apart for optimal vane performance. We also use a 1/8 deg. offset instead of a ½ or full degree of helical like most large manufacturers. This final element helps to eliminate drag which will create greater KE which means a more ethical hunting experience.
This is a quote from a article we wrote for the August 2015 CROSSBOW MAGAZINE about crossbow performance, and the benefits of CUSTOM BOLTS.