Space Age Arrow Flight

Here’s the big billy Robb took in Alaska.

This was it. All the preparation, all the target shooting, all the pre-season scouting, all the gym time and road work — it all came down to this. After six hours of climbing along the edge of a glacier the size of the state of Delaware and gaining almost 2,000 vertical feet in elevation we were finally above the little band of three mountain goat billys. It was a crisp October day in coastal Alaska’s Prince William Sound, and Mike and I had been watching these goats for several months as we waited for them to move into a spot where we thought we could both shoot them and, just as importantly, where they would not fall someplace impossible to retrieve them.

We played the sneak & peek game, creeping to the edge and peeking down, looking for goats. Nothing. Nothing. Nothing. Ohmygawd, there’s one, he’s bedded right below us! I slipped over the edge, sneaking slowly on my butt, only having to creep 75 yards before I’d be point-blank.

But then the billy, for some reason, got up and started feeding away from me. No!!! He disappeared behind a hump in the terrain and I knee-crawled to it as fast as I could waddle. Peeking over I saw him, feeding slowly away from me. Quick, hit the rangefinder! Fifty-five yards…nock an arrow, clip the release on, draw, split the 50 and 60 yards pins, he’s going over the edge, launch it!

The arrow arced high above his back, then disappeared in the glare of the icy glacial background and his thick white coat. But my aim was true, and the big billy lay stone dead not 75 yards from the hump, my broadhead having blown through both lungs.

That’s what cutting-edge bowhunting is all about. You plan and tune gear and keep your body in shape all year long for the chance to shoot one arrow under less-than-ideal conditions. Everything is riding on that one shaft flying like a Patriot missile, not a Scud.

When your body gets contorted during the shot and form isn’t perfect, knowing that your arrows will fly like a bullet gives you the confidence needed to make the shot.

As the above scenario illustrates, for bowhunters it all comes down to one thing and one thing only – regardless of conditions, can you place your broadhead into the vitals of whatever animal you are hunting on the first shot? For that to happen you of course must practice your shooting, maintain good form, not let “buck fever” bite you in your Fruit-of-the-Looms and be shooting a bow-and-arrow combination that is tuned to perfection so that those broadhead-tipped shafts zip out there with nary a hint of wobble. And it all begins with the arrow shaft.

The Spine’s the Thing

An often-overlooked but extremely important part of choosing the right arrow shaft is arrow spine. The Archery Trade Association defines spine as “a) The amount of bend (deflection) in an arrow shaft that is caused by a specific weight being placed at the center of the shaft, while the shaft is supported at a designated span; b) The recovery characteristics of an arrow that permits it to bend and recover to its original shape in flight.”

In layman’s terms “spine” refers to the stiffness of an arrow, and is usually denoted as the three-digit number on the side of most of today’s carbon arrows. Static spine is determined by first supporting a 29-inch shaft at two points that are 28-inches apart. Then an 880-gram (1.94 lbs.) weight is suspended from the center of the arrow. The number of inches the arrow deflects (bends) X 1,000 due to the weight is the spine size or measurement of an arrow. So, a 500 arrow bends .5-inches when the weight is applied.

Spine alignment refers to locating the spot on the arrow where it bends the least. “Each carbon arrow has a spine running the length of its shaft,” Victory Archery president Steve Greenwood told me on a 2016 tour of the company’s Poway, CA headquarters. “Through the manufacturing process, there’s always a spine where the arrow is the strongest and flexes the least. When we do spine alignment, we are also checking for straightness. We twist each shaft 365 degrees to precisely locate the spine. While doing that, we’re ensuring the most accurate straightness classification as possible. Spine alignment makes a huge impact on arrow grouping, especially at longer distances.”

For consistency, Victory places the cock vane of each arrow along its spine, which is shown by a white line silkscreened on the surface along with the arrow’s other designs. When choosing arrows you match the shaft’s spine to your own personal draw length and the draw weight of your bow.

When you have trouble paper-tuning a particular shaft with a particular bow, often it is an issue of spine. You can make sure you choose the right spine by using a manufacturer’s arrow selection chart, but keep in mind that both the size and weight of the fletching and the length and weight of the arrow point or broadhead can affect an arrow’s spine. That’s why you must paper-tune finished hunting arrows to make sure you are getting dart-like flight regardless of what the selection chart says.

How Straight is Straight Enough?

A typical human hair is about +/-.002-.004-inch in diameter, so even a basic aluminum or carbon shaft of +/-.006-inch straightness is quite remarkable and much straighter than you could possibly perceive without specialized equipment. While I want my shafts perfectly straight, manufacturing tolerances make that a pipe dream. However, shafts that are straight to +/- .003-inch are adequate for most hunting situations — though today’s top manufacturers offers premium shafts with a straightness as little as .001-inch.

: For most whitetail hunting — done from stands with shots less than 40 yards in a controlled environment — standard-diameter shafts with a straightness of +/- .006-inch are perfectly fine.

For example, the Victory Archery VAP Elite line, Easton’s 5mm Axis – Match Grade and Gold Tip Hunter Pro arrows have a guaranteed straightness of +/- .001-inch. Carbon Express Maxima Red shafts are .0025-inch or better. The list goes on and on. In terms of pricing, in the carbon arrow game, a dozen shafts with a straightness of +/-.006-inch can cost half as much as those with a straightness of +/-.001-inch.

Shaft Diameter

Arrow shafts come in different diameters, another important consideration. Most “standard” shafts are 6.5 mm in diameter. Some are a bit smaller at 6.0 mm. Then there are so-called “micro” diameter shafts at 5mm, and “ultra-micro” diameter at 4mm. (Each arrow maker calls their shafts something unique, but this is pretty standard.) So, which is right for you?

For most all close-range bowhunting, any of the above will work nicely, providing plenty of accuracy and penetration potential. However, for longer-range shooting or where you may encounter strong winds, the smaller-diameter shafts offer a smaller profile for the wind to push.

Robb’s final step is shooting at distance at both bullseye and life-sized 3D targets to make sure his shafts fly perfectly and group tightly.

This same smaller diameter helps increase penetration. The downside to the smallest diameter shafts is that they are too small to accept standard broadhead ferrules, which means you have to glue an adapter onto the front end of the arrow. This can cause problems if this part isn’t attached perfectly straight, though most of these components today are built so precisely that this isn’t a real problem.

Weight Distribution

Experienced archers know that for maximum stability in flight and optimum accuracy you need to have a bit more weight forward of the shaft’s centerline than behind it. This is most often referred to as weight/forward balance.

In the “old days,” bare shafts came as tubes of aluminum or carbon that were then cut to length, with nocks and fletches then added to the back end, and an arrow point insert and, ultimately, an arrow point to the front end. The weight differential between the components (and adhesives that hold them in place) created a different weighting on the front and back end of the shaft. Because the components – most notably the arrow point – weigh significantly more than those on the back end, the arrow had a weight/forward balance ratio that favored the front end. This is a good thing.

When your body gets contorted during the shot and form isn’t perfect, knowing that your arrows will fly like a bullet gives you the confidence needed to make the shot.

There are a couple of ways to alter the weight/forward balance. The easiest and most common is to adjust the weight of the arrow point. Obviously, a broadhead weighing 125-grains will put more weight forward of the centerline than one weighing 100-grains. Another way archers have been helped in recent years is by manufacturers that have added a little weight to the front of their shafts. One example is the Carbon Express Maxima RED SD shaft, which has stiffer ends to contain the arrow’s flex to what the company calls the RED ZONE. The RED ZONE is the section of the arrow shaft engineered to contain Dynamic Spine and make a broadhead shoot more consistently. I’ve shot them a lot and really like them.

To determine the weight/forward balance point of your own shafts, measure your overall arrow length with broadhead attached. For example, if it’s 30 inches, your midpoint is 15 inches. Mark this spot on the shaft with a felt pen. Now move one finger forward under the shaft until it balances itself perfectly on your finger tip. That is your balance point. In this case, say that is three inches. Mark this spot with the felt pen. Simply divide this distance by the overall arrow length and you’ll have your weight/forward balance percentage. In this case that is 10 percent. The ideal weight/forward balance on a hunting shaft is generally somewhere between 8-15 percent of the arrow length.

Putting it all Together

It all boils down to placing the first shot on the money. Here is Robb’s arrow heading toward his South Africa Cape buffalo…

In my little home shop I keep a very important piece of equipment that helps me assemble a quiver filled with identical hunting shafts. That tool is an electronic grain scale, the same one I use when handloading rifle ammunition. When I get a dozen fletched hunting shafts back from my pro shop, I weigh everything. First, I weigh the finished shafts without an arrow point. I then weigh each and every broadhead. You have to realize that due to standard manufacturing tolerances, even the very best manufacturers do not produce a package of broadheads wherein all broadheads weigh exactly the same. Thankfully, today’s tolerances are such that heads from top manufacturers weigh very close to their advertised weight, and the disparity between individual broadheads is small.

…and the results minutes later.

I assemble my hunting arrows and then weigh each finished arrow. I want my quiver to contain shafts with a weight disparity of no more than +/- 5 grains, and work very hard to build a dozen finished shafts that weigh within +/- 2 grains.

After weighing the finished shafts, I spin each broadhead-tipped shaft on the broadhead tip to check for possible wobble that indicates a slight bend that will throw off accuracy. If I find one that wobbles I mix-and-match shafts and broadheads until I get no obvious wobble. If I have a shaft or broadhead that simply will not spin, I don’t mess with it – I throw it away.

Next comes shooting through paper. I am a fanatical paper-tuner, accepting nothing but perfect bullet holes from my broadhead-tipped arrows. Remember that due to individual differences in shooting form, achieving perfect bullet holes for me may require slightly different tweaking of the rest position than it does for someone else. I test each and every one of my hunting arrows before the final step, which is heading to the target range and shooting every one of them from 20 yards to long distances.

When I’ve got my arrows grouping tightly at distance, I know both they, and I, are ready.–Bob Robb


Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.