Ruminations on Archery Ammunition

[konrad]

Ruminations on Archery Ammunition:


Once, not too long ago, in the annals of firearms history there was a group of “experts” who proclaimed “No one can reasonably expect to hit a single man at 100 yards with a gun on the first shot.” Of course, the men who proclaimed such idiocy had never considered the idea of a rifled barrel or aerodynamically shaped projectiles. In the quest for the ultimate in accuracy and long range performance, most firearms manufacturers now focus on tightly controlled land and groove diameters, consistent barrel profiles, bore finish, action bedding and good muzzle crowning. Projectile manufacturers concentrate on jacket/core concentricity, weight and shape quality controls.

In the firearms world, it is widely recognized that projectile spin rates dramatically affect accuracy. Spin rates, depending on the weight, length and velocity of the projectile, have been categorized thoroughly. That fact lays in firearms manufacturers standardizing barrel twist rates for the most commonly used projectile weight in any given caliber using standard velocities.

Applying this hard-won knowledge to archery only makes sense to me. Why do we not see published charts with columns containing arrow weight, launch speed and optimum fletching offset or helical twist?

 It continually astonishes me when I hear or read an otherwise knowledgeable archer make a statement like “you are not a shooting machine” or “you will never notice the difference” or “there is no such thing as perfect arrow flight” when discussing arrow straightness or fletching twist rates. It also strikes me as strange how those same folks will rush to a Hooter Shooter and go to the trouble of “tuning” arrows by rotating nocks to achieve the best groups possible and ignore the evidence of what they are attempting to work around…“spline”. In this case, spline being defined as a line extending the length of the shaft, usually a material over-lap construction defect occurring during shaft manufacture that makes one side of the arrow stiffer than other locations around the shaft circumference.

If our archer is determining shaft spline location he is attempting to apply a “solution” or “work-around” to a manufacturing problem within the shaft. I submit that if a group of shafts exhibit spline location preferences when grouping at 20 yards, the existence of that spine or hard lengthwise portion of the shaft of necessity implies imperfect wall concentricity and/or density. The stiffer portion of the wall must, by definition, be heavier than other portions of the shaft. Therefore, these heavy, lengthwise internal phenomena must negatively impact in flight rotational stability. That instability will most probably not be compensated for by the action of fletching. I would presume that given enough tail drag and spin even the most poorly constructed arrow shaft will fly to “acceptable” accuracy standards at twenty or so yards.

If, in the world of firearms projectile industry, jacket and core concentricity were not important, why would there be so much attention focused in that area? If one compares time-of-flight to the target at 100 meters between a round leaving the venerable 30-06 and an arrow launched from a 70 pound draw compound bow, the arrow has a much greater opportunity to be negatively impacted by this type of inconsistency. I submit these built-in irregularities are the primary cause of poor long range accuracy in modern archery ammunition.

If one accepts the realities of the existence of spline in most carbon arrow manufacturing processes, one must also accept that the measurement of spine (the resistance of a shaft to flexing) on any given arrow of this type could only be taken as an average of measurements around that shaft and it is a far less than a perfect way to categorize the stiffness of a set of shafts.

I would also beg to differ with some folks’ opinion that static spine and dynamic spine “have nothing to do with one another”. To the uninformed a statement like this is obfuscation at its worst. To the informed, the opinion is ludicrous. It is well known that information regarding the dynamic properties of a given material can readily be extrapolated from static testing. It may be true that complete understanding of stress fatigue failures can only be obtained through dynamic testing but data collected from static testing is well proven to be an excellent guide in selecting suitable materials for any given application.

This all leads me back to “You’ll never know the difference.”

Really???

Today, folks with firearms make successful hits on very small targets at ranges exceeding one mile. It was only a few years ago that some thought it impossible to hit those same targets reliably at 100 yards.

In this era of highly advertised, very profitable carbon composite arrow shaft construction, I wonder how so many otherwise intelligent archers ignore the virtually perfect lack of spline in modern aluminum alloy arrow shafts. Are archers as a group so easily stampeded by advertising into the “latest and greatest” craze? It would appear to be so.
How is it that only one company can make the claim that their archery ammunition products have won EVERY Olympic medal in modern history and the basis of those victories is rooted in a super consistent alloy tube?
 
I also wonder why, in an age of chronographs, high speed videography, personal computers and spread sheets; we still have no reliable data regarding weight, length, speed and rotational velocities of arrow projectiles and how best to stabilize them?

For you folks shooting wood, remember, God loves you too!

[buckfvr]

Its spine........was the article like that when you copied and pasted, or is it your mistake ?? 

[hughjorgan]

Spine is referred to in two different ways, static and dynamic

Static spine is the measurement achieved when you place the arrow shaft on a spine testing machine and place a weight on it spanned @ 28" and measure the deflection.

Dynamic or shot spine is the amount of flex that is developed when the arrow is in flight.

Spline is the point on the shaft where the material was lapped when the arrow shaft was made.

The spline or heavy/thick point along the arrow shaft can be found by plugging the ends of the shaft and floating it in a bath tub. The heavy side will move to the bottom as the arrow floats. The second method is to place the shaft on a arrow spine tester and place the weight on the shaft. Rotate the shaft and watch the deflection of the dial indicator. When it reaches it highest or stiffest point you have found the spline of the arrow shaft.

Finding this point on a given group of arrow shafts is a very effective way to bring consistency to the flight of a group of arrows.

Arrow manufactures have a parameter they apply to grouping arrow shafts by spine. They will measure the static spine and group them within a industry standard variance. Typically when you buy a set of 300 spine arrows you will get arrows that are somewhat stiffer and somewhat weaker than the 300 spine.

Occasionally you will have 1 or 2 arrows that are at the lowest or highest point of this parameter and wont fly quite as well as the rest of the shafts. Aligning the spline on these shafts will in many cases save you from discarding them.

Also finding the spline of a group of shafts and indexing the nocks so this thick wall is at the same location will improve the consistency of a given group of arrow shafts.

This process has been used for many years by competitive shooters. Until recently it wasn't typically used by hunters.

[Todd_ID]

Its spine........was the article like that when you copied and pasted, or is it your mistake ??

Oops!  Three straight strikes against the buckster.  If it was an article you read somewhere, then it was because he wrote it, I'm thinking.

[Todd_ID]

I appreciate your thoughts there Konrad, and I agree with what you're getting at.  I guess I fall into the category of guys telling people, "You'll likely never see it."  Many of those I help and shoot with are far less than perfect archers; a 36" bag needs a backstop at 30 yards type of shots.  For them, that statement fits no matter how perfect the equipment gets; I tell them to just go to the archery shop and buy a dozen arrows.  Those friends who I'll make up a dozen arrows for who happen to be good to very good shots I will take the time to spine check, spline, and weigh the arrow before putting vanes on in a matching orientation in relation to the spline.  Those that get that extra day of prep work love their arrows and say they all shoot consistently.  I write the spine and weight on each arrow so they know why that arrow is different.  When a guy puts 5 arrows in his quiver that are all within .001" on spine and 2 grains on weight, then he's got all the confidence in the world that his arrow won't be the cause of any future problems; even though it took buying and sorting through 3 dozen arrows to find those perfect 5.

With that being said, I still use a random amount of offset because I know of no datasets to use as a guide on rotation; I simply try to get as much as I can without compromising the glue joint.  Back when I was smart I had plenty of schooling on physics, calculus, strengths of materials and aerodynamics, but I don't have the brains to come up with the answer any more.  Bullets spin at a much greater rate than arrows, but archers don't really have the ability to speed the rotation up enough to be too fast like you can with a barrel twist, in my opinion.  I think all we're trying to do with spin is even out the inconsistencies a bit.  I honestly think it's in a primitive state physics-wise because the right answer is unattainable with today's equipment; it'd take a rifling-like apparatus to spin a much lighter, stiff arrow at a much higher speed; then Snapshot would be right, and our seasons would be cut because we could make a reliable shot at 100 or 150 or even 200.

I do know that the 3 dozen Carbon Tech Cheetah 3D that I made up were basically perfect as far as I could tell with my equipment for spine and spline.  Equal spines across the dozen (and around the axis of each arrow) and imperceptible spline made for great flying arrows.  (No, I'm not a rep or a seller of anything.)

To keep a long story short, I now shoot wood.  You can see the spline in the grain, and they're never straight or close in weight or spine.  Max offset, too.  And, yeah, I need a backstop...at 20.

[RadSav]

hughjorgan - dang good bit of writing there!

As far as the main post...keep asking questions and you'll come up with a few more answers and clarification.  You're on the right track.  Just not enough questions yet to find the right answers.  Add pultruded carbon shafts into the mix for some additional fun.

Remember that static testing will only give you information from zero to a specified threshold.  Whereas, dynamic testing usually starts at a point beyond that threshold then back to zero.  They are common yet opposite at the same time.

It's fun and sometime valuable to get this far into the art, science, supposition and conjecture of arrows.  But, until you eliminate the human aspect of the shot few will ever see the difference or benefit from such.

[hughjorgan]

hughjorgan - dang good bit of writing there!

As far as the main post...keep asking questions and you'll come up with a few more answers and clarification.  You're on the right track.  Just not enough questions yet to find the right answers.  Add pultruded carbon shafts into the mix for some additional fun.

Remember that static testing will only give you information from zero to a specified threshold.  Whereas, dynamic testing usually starts at a point beyond that threshold then back to zero.  They are common yet opposite at the same time.

It's fun and sometime valuable to get this far into the art, science, supposition and conjecture of arrows.  But, until you eliminate the human aspect of the shot few will ever see the difference or benefit from such.

I didn't write that, it was actually written by a guy on AT. I just cut and pasted it for everyone else to read.....

[RadSav]

Really!  An intelligent person on AT?  Not sure I believe that.  From my experience it's just an inflammatory site of misguided souls.  Perhaps things are changing

[Matt]

Really!  An intelligent person on AT?  Not sure I believe that.  From my experience it's just an inflammatory site of misguided souls.  Perhaps things are changing

Just like anywhere on the internet.  Ya gotta weed through the BS to find the facts.  There are definately some very knowledgable folks on AT, you just need to know who they are.

[DIYARCHERYJUNKIE]

Great read and I'll be tuning all of the arrows I shoot this year.  Thanks for the info.