How can I increase arrow/bolt stiffness?
Ways to improve arrow/bolt stiffness include:
1. Shortening the arrow
The shorter the arrow is, the stiffer the shaft, the higher the FOC, and the less surface area to be affected by cross winds.
However, the shorter the arrow, the shorter the rear lever arm of the arrow becomes, which makes it more difficult for the fletchings to correct flight. In tests with the 375-grain broadhead, a 22-inch Zombie Slayer arrow ultimately offered cleaner and more accurate flight than a 20-inch arrow, so shorter does not necessarily mean more accurate.
2. Choose the stiffest quality arrows
Stiff, high quality arrows tend to also be the most expensive. For crossbow shooters, as of Jan 30th, 2022, Black Eagle Zombie Slayers are the stiffest 18-, 20-, and 22-inch crossbow arrows on the market, and are approximately 25% stiffer than the Black Eagle Executioner arrows. If your crossbow accepts arrows shorter than 18-inches, choose something shorter.
Archers may select a stiff arrow such as the Black Eagle Rampage 150 spines or the Grizzlystik TDT 170 spines. If you an archer and need assistance with arrow build and selection, Rob Hummel at Dynamic Archery Solutions (not affiliated with Edgetac) can assist. Rob has set up and shot Edgetac 375 and 775 grain heads accurately from his bow.
3. Use of aluminum arrow footers or “shock collars”
Adding aluminum footers to the arrow is a great way to stiffen the dynamic spine of the arrow, and it results in an arrow that is far more durable. Crossbow shooters can construct their own footers using aluminum pipe that has a 9mm inner diameter and a 11mm outer diameter. Vertical bow shooters have the option of choosing commercially available “shock collars” and footers. Some archers tune by adjusting the footing length rather than the shaft length.
Double shafting is how many build stiffer bolts. Double shafting will reduce FOC, but a much stiffer and more durable shaft will result. Ideally try to find a shaft with an OD that is a few thousandths smaller than the ID of your current bolt. One of the stiffer arrows available is the 200 spine Rampage from Black Eagle. Its OD is 0.285. When choosing the internal shaft for a double shaft arrow build, typically look for as stiff a spine as possible. The lower the spine number, the stiffer the arrow. Typically 150 and 200 are the stiffest arrows typically seen in production. The only downside to double shafting is the cost and the lost FOC, but it’s logical to accept lower FOC if it means clean flight.
For crossbow shooters, enhanced stiffness arrows can be constructed by taking standard crossbow arrows, which have an inner diameter of 7.62mm, and inserting the stiffest possible carbon archery arrow blanks, or carbon fiber tubes, with an outer diameter of about 7.5mm.
5. Adding weight to the tail of a shaft
This can resolve minor spine issues, but when combined with high levels of FOC it can get messy. High levels of FOC essentially make the tail easier to move in flight and thus have a faster recovery, but that fast recovery is dependent on tail recovering and staying recovered. Adding additional mass in this situation gives the tail more inertia and when combined with too much flex it can actually make it worse because the tail will overshoot “center” by a larger amount. There’s a limit in how much weight can be added to the tail and in a situation where there is a high FOC, a fair amount of weight would be needed to actually make a difference in the amount of flex occurring.