Tuning Series -- Dynamic Arrow Tuning
Dynamic Arrow Tuning
Carbon arrows are a material matrix, slight variations sometimes resulting even within a single deflection grade. Expensive, super-straight arrows come off the same mandrels as budget-priced arrows with lesser tolerances - various grades resulting from sorting, higher costs relegated best-spec shaft because fewer make the cut. Though today even lower-grade arrows are normally sorted into matched-weight groups.
Now, just because arrows are laser-inspected for straightness doesn't mean spine around their entire axis are preciesly equal. All carbon arrows include seams; the starting point of the wrapping process around shaping mandrels. A few manufacturers mark this seam (normally the stiffest deflection point); most do not.
Still, buying the best arrows possible is a good investment, more carefully culling duds if nothing else. Many experts downplay straightness, pointing to even deflection around a 360-degree axis as most important. I'll buy this, but still feel most confident while shooting the straightest shafts I can afford, especially with broadheads.
That said, less-than-perfect carbon arrows can be "tuned" to an extent - something I call dynamic tuning. Manufacturer's spine/deflection ratings are established through static spine, meaning how much shafts flex on a 28-inch span with about 2-pounds of weight applied to the middle, related in inches; i.e. .500-inch ("light" spine, lots of flex), .300-inch ("stiff," less flex). Dynamic spine indicates how arrows behave during launch from a specific bow, wearing a specific point weight.
Tuning arrows begins with establishing a nock-end starting point on each shaft - a pen mark or existing cock vane - nock oriented to mark. Now fire a single, field-point-equipped shaft at a fine point from the maximum distance you can assemble reasonably-tight groups. Shoot the shaft and note impact. Rotate nock 1/8-inch clockwise (this works best with drop-away rest, as fletching orientation becomes less critical) and shoot again. Another option is Outer Limit Archery's Blood Vane, allowing rotating a three-fletch/arrow sleeve to correlate to each new nock attitude. Continue test shooting until discovering an axis point where the shaft impacts spot on. Mark it carefully.
Now take each arrow in the group and continue the process, finding that single sweet spot around each arrow's circumference allowing it to best group in a single spot. After all shafts are marked, refletch if desired to create identical fletching attitude on the set.
You might deem this unnecessarily tedious, maybe even anal. I somewhat agree, as most of today's best arrows group better than most of us are capable of shooting. But, dynamic tuning does allow you to purchase cheaper arrows, those with straightness specs of, say, +/- .006 to .008, carefully tuning for tighter groups.
You can also fine-tune for balance by testing various head weights. Also, carefully weighing each broadhead on a precise reloading scale is wise, as some weight variations can exist. Balance tuning can occur in larger increments, testing 85-, 100- and 125-grain heads, or smaller degrees, using Precision Designed Products' 5-grain brass weight washers, to create tighter groups and strighter flight; or to assure all heads are identical weight.