Broadhead Arrow Spine Tuning
Improve your shooting accuracy with our expert step by step advice on spine tuning your arrows.
Once we have found the “sweet spot” in our cam and have increased our bows forgiveness, now is the time to really get aggressive with finding the “Sweet Spot” with our arrows. I like to call this “Spine Tuning”.
It is not an absolute necessity for a modern center shot compound bow to shoot with perfect spine, but it sure lends itself to more flexibility and forgiveness. Many manly men who want to be known as the resident wiener measuring champions despise Spine Tuning.
Their personal happiness and social standing rests within the digital read out on a Chrony. For those guys who proclaim speed is everything, this little thing is not for them. But to those who believe life is more than social endowment this may lead to further enjoyment of the sport through consistent repeatability.
How to Spine Tune
The easiest way to “Spine Tune” is with a broadhead tipped arrow. I will often times spine tune using a broadhead larger in cutting diameter than what I might shoot in the field. If these broadheads have an equal weight to my chosen hunting head, they will exaggerate the effect of an arrows spine while applying an equal amount of resistance and effect. The more dynamic the effect, the easier it is to fine tune the bow to work with a chosen arrow’s spine.
A properly spined arrow, or more appropriately, a bow properly tuned to an arrow’s spine remains more forgiving to changes in point weight, point shape, weather changes, poor releases and breakdowns of shooting form in general.
A major reason I spine tune is that I test so many different broadheads throughout the year. A proper spine assures my base line remains constant. It often allows me to use the same arrow for testing 85 grain, 100 grain and 125 grain broadheads.
As a bowhunter, this allows me to shoot arrows all day to stay in shape. I can shoot steel blunts at stumps and dirt, Bludgeon blunts at grouse, Judo points at clumps of grass and any number of small game points at rabbits or other vermin without the need to change point of aim or adjust my sight block.
This really increases my enjoyment during those slow hunting days and greatly improves my odds when off season small game or stumps is my chosen quarry. Target practice is one way to improve success, but off season and during season field practice will even further assure your success when that trophy presents itself!
How to Select the Correct Arrow Spine
Since we have creep tuned in the previous article, we already have a horizontal piece of tape on our target and a target point arrow tuned to hit its center. So, let’s use this as our base line once again. All we want to do is get our arrows into the center of the horizontal stripe. Grouping is done by moving along the stripe/tape left to right, so we don’t ruin arrows with well executed shots.
I use a three-arrow row for this base line. Next step is to shoot our broadhead tipped arrows at the same line once again being careful to group left to right along the horizontal line, so we don’t ruin arrows with well executed shots.
If our broadheads hit the same place on the stripe as the field points, we move on. However, if they do not, we need to adjust our nock height or arrow rest height. If we move the nock point or arrows rest in 1/32″ increments the broadheads should move at an average rate of 3X that of our target points.
On a true center shot compound arrow spine may reflect in a horizontal or a vertical direction. With these bows we need to remain diligent in our ability to take notes and recognize changes.
If a 1/32″ adjustment in our nock set or our arrow rest does not narrow the gap between the target points and the broadheads it is likely a spine issue and not a nock height/rest height issue. So we will address that later.
If the 1/32″ adjustment is successful in narrowing the gap we want to continue 1/32″ at a time until the gap either stops improving or the two type points both hit in the middle of the horizontal line. This is where micro adjustable arrow rests really pay off!!
Once we have established our best rest/nock height setting (even if our two arrow points are not yet together) we move on to shooting at a vertical stripe. A carpenters level is a great way to make sure our line is true vertical! You can use a bright colored string and a plumb bob with good results too.
Here again we want to establish a base line with our target point arrows grouping along the stripe/tape. Does not matter whether we group in a down to up or an up to down progression. And once again we want to move our arrow rest 1/32″ at a time in an attempt to bring the broadhead point arrows and the target point arrows together but stopping if the 1/32″ movement in arrow rest adjustment produces zero change in the gap between the two or the two have successfully come together.
Now we should have our arrow rest and our nock height set to their optimal locations.
This is where the Spine Tuning Magic Happens
Since our Creep Tuning has resulted in a perfect timing within the cams and limbs the odds are that any improper spine will be reflected in the vertical stripe rather than the horizontal stripe.
But do not be concerned if that is not what your notes and target is telling you. Regardless as to what direction the spine favors to show itself there should be a clear picture toward which stripe (vertical or horizontal) has the largest remaining gap between broadheads and target points. At this time, we want to once again establish a well-defined base line with the target points on whichever stripe proved to possess the largest gap.
I am going to assume that the percentages and laws of force have shown a larger gap between the broadheads and the target points on the vertical stripe. Under this assumption we can conclude that broadhead tipped arrows hitting to the right of our base line are too weak in spine and broadhead tipped arrows hitting to the left of the base line are too stiff.
If an arrow is spined too weak, we want to work in 1/4 turn increments to weaken the poundage of the bow. It may take a number of adjustments before we start to see the broadhead tipped arrows begin to work their way toward the target points. It all depends on just how weak the spine was for the bow.
You will want to do the exact opposite for a spine that is showing too stiff. In this case we want to increase the poundage of the bow in 1/4 turn increments until the two come together.
Important Spine Tuning Notes
Be careful to follow the manufacturers advise on how many turns are safe when backing off the limb bolts to reduce poundage!! If you are unable to decrease or increase the poundage enough to bring the two type points together you may need to change the arrow spine altogether. If this happens you will need to start the process all over once you possess the appropriate spined arrow.
Once you have the two points on the same line it is time to maximize its forgiveness just as you did in the “Creep Tune”. To do this you will want to back off poundage until the broadhead tipped arrows POI just begins to leave the base line. Then counting turns increase the poundage until the broadhead tipped arrow just starts to leave the base line again.
Divide the total number of turns in half and back off the poundage that amount. Your result should leave you with the most forgiving finely tuned spine for your bow, your chosen broadhead and your shooting style.
Whatever your poundage is and whatever your speed works out to be it should still provide you with a better more enjoyable bow to shoot. Those in Washington State will need to remember to check their grains per pound to be sure you are still legal because of that ridiculously stupid ruling that our arrows must weigh at least 6grs per pound of draw weight, with a minimum of 350grs.
This is a labor intensive process and may need multiple days at the range to complete depending on your fatigue level. As such many feel it is too much work for too little reward. But to me, it is one of those little things that adds mental strength and improves my confidence in big ways. This is an important step toward my enjoyment of the sport.