I saw the new FMJ Bolts about a week ago when I was doing the testing work which you are about to see. The problem with the new FMJ's even if they were available in a longer length is that they don't have a stiff enough spine to support these crossbows and there are no plans on the boards to change that. That was confirmed from within Eastons Advisory Board.
I know everybody has been waiting for my reply and it’s been too long, but I’m hoping the wait was worth it after you read my input.
I’d like to take this from a slightly different angle than Super 91 has already done and hopefully see if I can simplify the explanation so the masses can understand what we’ve found. I'll also attempt to simplify the steps in the accuracy solution, so even the masses can follow them.
For some of you this will be basic information that you probably already know. For the rest it’s material that you should probably put to memory and retain for future use.
The original problems that we’ve been chasing have been how to attain the best possible arrow groups over longer distances (60 – 100 yards) with the PSE TAC15 Arrows.
When shooting the same arrow repetitively a shooter can easily attain sub 2 – 3 inch groups at 100 yards, but the moment you move to a different arrow shaft the groups open up significantly and this type of accuracy is lost.
After extensive testing with some very well known people that shall remain nameless for the purpose of this article, we have identified some key reasons for this problem.
It’s very important for me to state before we go any further that everything that I now will speak about is outside the realm of any manufacture issues or responsibilities. When it comes to fine tuning and balancing arrow flight to this degree, it’s a competitive edge that is well outside of any arrow manufactures production work. Therefore to attain the highest degree of performance from ones equipment these are the additional steps necessary to achieve that end.
Our testing on two dozen disassembled shafts yielded two or three basic statistics that would account for the type of grouping behavior that we’ve been experiencing.
The issues were as follows:
Arrow Spines not aligned the same on each arrow and indexed to the arrows nocks.
Shaft deflection ranges different from arrow to arrow.
Finished arrow weights somewhat inconsistent to the 100th of a gram.
Each of these factors will play a role in causing an arrow to fly perfectly straight in relation to each other and therefore will cause different amounts of shaft flexing in different directions. This in turn will open up the placement of each shot group as the distances increase.
Most people think an arrow flies just like it looks when at rest - perfectly straight. But nothing could be further from the truth. Once fired from a bow, an arrow immediately begins flexing and oscillating. That's not a defect. Each arrow bends and flexes in a particular cycle as it leaves the bow (archer's paradox). If the timing of the cycle is correct, the tail of the arrow clears the bow without making contact with the arrow rest, riser, or cables. If the timing of the cycle is not correct due to improper arrow spine, the over- or under-oscillation of the arrow results in serious fletching contact and/or paper-tune tears which cannot be corrected. So we have to get spine properties right.
There are three main ingredients which determine an arrow shaft's general spine characteristics:
(1) The stiffness of the actual shaft material
(2) The length of the shaft
(3) The tip weight that will be used
But it's not quite as simple as 1-2-3. How stiff an arrow is when it's sitting still on the workbench, and when it's busy accelerating from 0-180 mph as it's fired from the bow, are totally different issues. When the arrow is at rest, we refer to its stiffness characteristics as static spine. But when that same arrow is in motion, its stiffness is a matter of dynamic spine.
Unless your arrow shaft breaks or is altered, its static spine remains the same throughout its life. But your arrow's dynamic spine can change dramatically depending on how it's used. The real meat-n-potatoes of arrow performance relies on the arrow's dynamic spine. The dynamic spine is how the arrow actually bends and flexes when shot - and there are many factors which affect the dynamic spine. As you fire the arrow, the explosive force of the bow compresses the shaft and it momentarily bends under the strain. The more powerful the bow, the more the arrow bends. This is based upon the physics of “Dynamic Arrow Spine Deflection”.
Arrow Spine Deflection:
Sometimes an arrow's spine stiffness is expressed as a more technical measurement, called a “spine deflection”. According to the modern standards (ASTM F2031-05) an arrow's official spine deflection is measured by hanging a 1.94 lb. weight in the center of a 28" suspended section of the arrow shaft (not to be confused with the old AMO standard of 2 lb. and 26"). The actual distance the 1.94 lb. weight causes the shaft to sag down is the arrow's actual spine deflection. For example, if a 1.94 lb. weight causes the center of a 28" arrow to sag down 1/2 inch (.500"). Then the arrow's spine deflection would be .500". Stiffer arrows will, of course, sag less. More limber arrows will sag more. So the stiffer the arrow is, the LOWER its spine deflection measurement will be. The more limber an arrow is, the HIGHER its spine deflection measurement will be.
If you test for spine deflection while slowly rotating the arrow, the spine deflection should remain constant. No matter which direction you bend the shaft, it should be equally resistant at all points, right? Nope! The wound layers of a carbon arrow will always have a seam somewhere inside the circle or a seam of some type that will be stiffer than all other points around the shaft. This is not unique to carbon since all materials will always have a spine if tested carefully. This creates an imbalance in the spine consistency of the arrow, such that the arrow is a bit more stiff at one point around the circle. It's unfortunate, but the process by which carbon arrows are manufactured inevitably results in some imperfections. And if you want to get really technical, most arrow shafts aren't even perfectly round for that matter.
But the important question is, does it really make a difference? From a pure physics standpoint, yes. But again, few shooters have enough skill to notice. Small amounts of spine variance are realistically inconsequential to the weekend bow hunter and backyard enthusiast, but as distance and accuracy increase these differences can produce significant deviations in arrow flight from one arrow to another, so we need to eliminate these variances if we want to gain the maximum accuracy that can be achieved from a given group of arrows.
Arrow Weight Differences:
At short distances or very high velocities minor weight differences produce very slight deviations in elevation on the face of a target, but as distance increases or velocity decreases these deviations are magnified. An example of this is as follows; an archer shooting a 28” arrow, at 60lbs., at a target 60 yards away will experience 4 inches of elevation difference on the face of a target, for each gram of arrow weight difference.
I believe it was Konrad who pointed out the importance of this factor, so I’m not going to define this one any further.
In this next section, I’m going to attempt to layout, in a logical progression the steps to isolate and correct each of these arrow tuning elements and explain what each step in the process corrects. None of this is based on theory, since we easily identified and corrected each condition to achieve the grouping performance we’ve been seeking.
Some basic essential tools needed to perform the following exercises will be a good arrow fletching jig (preferably the Bitzenburger multi-fletch w/ nock receiver #3012 - 60 x 120, 4 fletch), an electronic grain scale, an arrow spine tester (RAM Spine Tester or equivalent), Pliers, good glue for nocks and vanes, replacement vanes (3” Norway Duravane 3D 50 pk.), a white Pentel marking pen for marking spine alignment lines on each arrow shaft.
Before any testing can begin all arrows should be numbered from 1 – however many shafts you are testing. You will need at least a couple dozen shafts if you wish to come out with a dozen well matched arrows. You will also need a piece of paper to record your spine deflection readings and the specific weight of each arrow.
Step 1 – Using the white marker pen, place a small white line about ¼” long on
each the arrow shaft in alignment with the center of the top of the nock
and the same on the center of the bottom of each nock. These will be
used as reference points to let you know where the nocks were
originally aligned to the arrows shaft.
Step 2 – Next, grasp the shaft close to the nock with your bare hand and then
grasp the nock with a pair of pliers. Twist the shaft and the nock in
opposite directions until the nock breaks free from its glue bond, and then
continue rotating the nock back and forth until it’s out of the arrow shaft.
Clean any residue from the nock and save it for the re-assembly process
Step 3 – Remove all vanes and glue from each arrow shaft. This is the most time
consuming part of the process. This can best be done using a good single
edge razorblade or a utility knife, but be careful not to dig the knife into
the carbon and do not cut yourself. Angle the knife as though you're
taking thin slices from the shaft and the knife should slide easily along the
surface of the carbon to remove any glue residue. The vanes just need to
be sliced off and are not re-useable, so make sure you have new ones
before you begin this project. Using denatured alcohol on a cloth and
wiping the shafts before and after removing the vanes is very helpful in
loosening the glue residue, removing surface dirt and skin oils from
Once all shafts are clean and all glue residue has been removed you are
ready to proceed to the testing phase.
Step 4 – Unscrew the 85 grain field points and save them for the re-assembly
phase of your shafts.
Step 5 – I am not going to recommend the removal of your arrow inserts because
we have learned that the TAC 15 arrows use a special 2 piece insert and
the front of each arrow shaft is beveled out to accept these inserts. This
process adds greatly to the strength of these shafts and is not made
to be removed, so the manufacture uses a permanent bonding cement at
the factory. It shouldn't be necessary to remove these inserts for the
type of testing we are doing here.
Step 6 – Using the spine tester, place each arrow shaft on the tester, after the
tester has been calibrated correctly and your 1.94 lb. weight has been
placed in the center of each arrow shaft. Very slowly rotate the shaft while
watching the testers gauge. On a RAM Spine Tester you will be watching
for the highest reading on the gauge during a full rotation of the arrow
shaft. Once this point has been identified you should place a line on the
arrow shaft exactly in alignment with this point.
This marks the stiff side of the arrow shaft and will be transferred to the
same spot on the nock end of the shaft. This mark is where you will align
the center of each nock to insure all arrows spines are indexed identically
to their nocks.
Step 7 – While slowly rotating each shaft use a paper and pencil to record the
shafts number (the one you labeled on each shaft before you started) and
also record next to this the highest and lowest reading you obtained while
rotating the shaft. This will be represented as a decimal value by simply
placing a decimal point in front of the reading on the gauge. If you rotate
the bezel of the tester to zero before hanging the weight on each shaft
and record the number of full turns the indicator makes, this represents
your first number. The number the dial rests on indicates your next two
digits. So if my pointer makes one full rotation and then is then sitting
on 68 this would be a decimal value of .168.
Remember we are looking for the highest and lowest reading around the
circumference of each shaft. This is how “Spine Deflection” is
measured. Once all shaft spine deflection ranges have been recorded on
your paper it should be easy to see how many shafts have close to the
same amounts of deflection and how many are different.
Step 8 - This is where the shaft sorting process comes in. You now need to sort
and group your arrow shafts by Spine Stiffness and Spine Deflection
I’ve heard it said that a Spine Deflection range of + or - .005 or 5/1000 or
5 lines on your indicator bezel, makes very little difference at 20 yards
from a bow being shot by a Hooter Shooter. This is a mechanical shooting
device that is extremely precise and accurate. I personally always use a
variation of + or - .002 or 2/1000 or 2 lines on the testers meter.
I continue this process until I have as many shafts as I need to form my
final arrow group. I like two dozen matched arrows, but you can go with
your own preferences.
Like it or not the other shafts are never going to perform at long distances
the same as these matched shafts because they have entirely different
spine and flexing properties.
Whilst they may be Ok or useful at shorter distances (up to 50 yards),
they’re never going to give you the super tight groups and arrow to arrow
performance of the matched set you’re creating.
Often, I like to find other archers who are using the same shafts as myself
and arrange to trade them shafts that are outside the range that I’m
shooting, but match what they are shooting for their shafts, that fit my
range of spine deviation. This way we both gain needed shafts and have
much with less waist.
You will inevitably end up with a certain number of shafts that can’t be
used. I wish I had better news on how to make good use of them, but I
don’t. It’s just part of the cost of doing business when it comes to
Step 9 – Once you have your final shafts, we can begin the re-assembly process.
The first step is to place the nocks in alignment with the stiff side of the
spine markings that you place on the nock end of your arrow. It doesn’t
matter if the stiff side of the spine is aligned at 12:00 on each shaft, or
at 6:00 as long as it’s the same for each arrow all the time. When you
align the nock, make sure you do not push the nock all the way into the
shaft at this point in the process.
Step 10 – With the nocks aligned to the stiff side spine markings you can now
carefully begin the fletching process. Using the Bitzenburger Jig or
equivalent, carefully glue each of the four vanes back in place. If you
need assistance on how this is done, please see the video produced
by Super 91 on fletching the PSE 15 TAC Arrows. Once each vane is
dry, make sure you add an extra drop of fletching cement to the front
and rear of each vane where it contacts the arrow shaft. This helps
improve the bond and protect the vanes from lifting and coming lose.
Now please pay attention because it gets a little tricky from here.
Step 11 – Remember I said not to push the nocks all the way in, well here’s why.
This step requires you to weigh each arrow shaft and record its weight
on the paper where you listed the spine information. You will need the
electronic grain scale and you will now weigh each shaft and
record its exact weight in grams or in grains if you prefer.
Once finished you will select the heaviest shaft in your lot. Using a slow
setting good glue like Duco Cement or a twenty four hour Epoxy or any
other good glue, you will place a thin dab around the base of the nock
and insert it all the way in as far as it can go. If necessary use a table or
hard surface with a nock insertion tool to insure the nock is firmly and
uniformly seated. Immediately wipe any glue residue from around the
Now weigh the shaft and record this exact number.
This is the exact weight you will use on all other shafts to achieve your
final weight for each arrow. This will be achieved by adding just a little
extra glue to each of the other nocks during the insertion process.
Remember the first shaft you did was the heaviest, so all others are
lighter by varying amounts. When using a gram scale I like to keep all
arrows within a quarter of a gram between the heaviest and lightest in a
batch. On a grain scale there is a conversion, but I don’t have it off the
top of my head, but its easy enough to look it up. Konrad can probably
quote it better than I, so maybe he’ll respond after reading this.
Step 12 - Now screw in your 85 grain field points and let all the arrows glue dry for
24 hours while they stand.
You now have a set of fully matched arrows with matched spines, properly indexed nocks and weight matched finished shafts. The only other factor associated with the shafts that we can’t address is the straightness factor. A straightness of .003 is not optimal, but if you can shoot almost same hole groups at 50 yards with them, you should be able to now shoot consistent sub 3 inch groups at 100 yards, no matter what arrow you select from your completed lot. The tighter your sorting and weighing parameters are, the tighter your groups will be.
This is a time consuming process, but it’s been used successfully for many years by our top competitive archers. Don’t ever believe that anybody is just born with the ability to consistently shoot ultra tight groups unless they or somebody else they know has tuned their equipment to support their shooting abilities.
Last, if you’re wondering if all this work is necessary, I’ll leave you with one final thought and from this you can decide for yourself.
There’s an old saying that goes “Good Enough is the arch enemy of Better and Best”! If you believe these words to be true then the information above is for you. If you disagree with this statement then you don’t need any of this nonsense and can continue happily shooting what you have.
Well-written Jon. Once you know the steps to take, it takes longer to read this article than to complete a set. It might seem overkill, but this is only for those who want to squeeze all the accuracy that can be had out of your TAC. Keep your eyes open over the next month. I will be doing a video to verify our results.
I'm sure everyone who took the time to read this lengthy article realizes this did not take 5 minutes to put together. Jon should be applauded for his efforts here. Well-done Jon, thank you.
I am sure all will agree your investment of time and money is well appreciated.
As in so many other marksmanship pursuits, consistency is the key to success.
One gram is equal to 15.43 grains (You have gotten to know me well).
Thanks again and everyone always remember to be safe and have fun,
“The rifle itself has no moral stature, since it has no will of its own. Naturally, it may be used by evil men for evil purposes, but there are more good men than evil, and while the latter can not be persuaded to the path of righteousness by propaganda, they can certainly be corrected by good men with rifles.”