External rifle ballistics approach to archery and projectile stabilization.

[Adam0321/0306]

So I am an avid archer. I shoot competitions and hunt. I was recently trying to tune a boradhead for my hunting bow and am having a very hard time getting it to fly correctly. I can get arrows with smaller profile heads to group great at the desired distance. However, these new broadheads are all over the place. The only thing I changed was the broadhead. That is when it dawned on me that I have never seen a velocity rating on a package of broadheads.

Just some context for the non-archers, and I do not mean to insult anyone.

An arrow is comprised of the shaft which has a spine rating. This is essentially how stiff the arrow is. Arrows flex when they are shot. The more poundage you shoot, the stiffer the arrow must be. Adding a heavier point, changing the length of the arrow, bow poundage, type of bow, speed of the bow, and type of cams (the wheels on a compound bow) all affect the spine.

We then have the knock. The vane configuration that provides stability. And then we have the broadhead or point.

When an archer sets up an arrow, they chose the correct spine, cut it to length, fletch the arrow with 3-4 vanes or feathers, and select a broad head. The bow is also tuned properly to ensure that the arrow is fling out of the bow in the most perfect manner achievable.

Generally, we see very little problem getting the field point to group as they have a small profile. However, when we put a broadhead on our arrow, this is where things get interesting. We have to adjust things to get the heads to fly and group correctly.

I have been trying to get a certain head to group and I simply cannot. That is when it occurred to me.



Bullet manufacturers have calculators to estimate a bullet’s stability given its velocity, twist rate, weight, BC, and SD. We have never considered these with arrows.

External ballistics should be external ballistics regardless of the projectile. We have never given this much thought in the archery world because the bows are not that fast. A very fast bow only shoots in the low 300 FPS range. However, when you look at the surface area of a broadhead and compare it to a Berger 2155, there has to be a correlation somewhere.

Is there a formula to calculate estimated stability given surface area, drag coefficient, and velocity? If we think about the correlation between rifles and bow, and bullets and arrows:

A barrel twist rate is similar to the arrows vane configuration as they are both inducing spin to provide stability.

Speed and projectile weight would be the same values.

What we are missing in archery is the sectional density and ballistic coefficient of the projectile. And a proposed “stability factor” for the vanes as some vanes and vane configuration provide more stability (spin) than others. When we say projectile, we must think of the arrow and all of its components as the projectile.

So this is my question for the guys much smarter than I am. If we exclude shooters ability and form, and assume the bow is perfectly set up with a good arrow configuration. Is it possible that an arrow and become destabilized due to the surface area of the broadhead? Some of these heads are 2.5 inches in diameter and are being steered by small vanes in the back. I posted this on an archery forum and one member suggested that anytime the arrow head extends past the width of the vanes (the steering mechanism) then you would be simulating shooting a bullet backwards.

Thoughts on this? Thanks and be safe.

 

[Bc'z]

Unless it's a mechanical broad head, a fixed blade will also give you a steering effect.
I personally align my broad heads up to the leading edge of helical of the vanes as you sight down the shaft.

Things I have noticed is some broad heads fly straighter than others.

 

[DaveTooley]

Two different worlds.
One is spin stabilized the other is fin stabilized. Different aerodynamic principles apply to each.

 

[Adam0321/0306]

Two different worlds.
One is spin stabilized the other is fin stabilized. Different aerodynamic principles apply to each.

Is it though? The vanes induce spinning. An arrow never stops spinning as it flies through the air.

 

[Adam0321/0306]

Unless it's a mechanical broad head, a fixed blade will also give you a steering effect.
I personally align my broad heads up to the leading edge of helical of the vanes as you sight down the shaft.

Things I have noticed is some broad heads fly straighter than others.

Exactly, and is that because a head with a larger surface area requires more stabilization?

 

[Bc'z]

A bullet doesn't have paradox though an arrow does.

 

[Bc'z]

Exactly, and is that because a head with a larger surface area requires more stabilization?

Yes, the blades work as forward rudders.

I've seen broad heads that should have been against the law to sell, poorly designed and constructed and they flew like crap.
Bear Razors come to mind.

Shoot a field point and listen to the shot, now shoot a broad head.
I believe you'll find the broad head is more audible. This tells me it's getting more drag, on difference between the 2 shots is the head.
Best flying fixed blade broad heads I've found.
125gr Wasp, 100gr Montec G5
Both of these fly straight with least amount of sight adjustment from field point to broad head

 

[dellet]

Quite simply you would go back to the basics. Much of our modern or most recent Ballistics is rocket science applied to bullets. Rockets are fin stabilized, but have no paradox or bend when fired.

An arrow in some ways is not stabilized with the fletching, it is only stabilized faster. With a center shot bow, the answer is generally more spine, reducing the famous archers paradox, or bending of the projectile that is actually causing the instability. In an actual bow, where the arrow needs to bend around the bow it becomes more complex.

So you have multiple issues.

The simple answer is if you want the arrow stabilized faster, add fletching. The faster it stabilizes, the tighter the groups will be. The balance is that more fletching is more drag and weight, slower velocity.

More fletching generally means you will need more clearance at the sight window for the arrow to pass without the fletching contacting. That means less spine. You enter into an endless circle where the bow needs to be designed for the broadhead.

Then there is the root of the problem that some broad heads look really cool, and probably cut a mean hole, if only they could hit the target.

A 6 fletched flu flu will stabilize a brick tied to a stick, range becomes an issue.

 

[Adam0321/0306]

Yes, the blades work as forward rudders.

I've seen broad heads that should have been against the law to sell, poorly designed and constructed and they flew like crap.
Bear Razors come to mind.

Shoot a field point and listen to the shot, now shoot a broad head.
I believe you'll find the broad head is more audible. This tells me it's getting more drag, on difference between the 2 shots is the head.
Best flying fixed blade broad heads I've found.
125gr Wasp, 100gr Montec G5
Both of these fly straight with least amount of sight adjustment from field point to broad head

In the scenario I am describing, I can get my 100 grain Montecs to group just fine. But the 100 grain Ser Razors I can barely keep in the target.

 

[Adam0321/0306]

Quite simply you would go back to the basics. Much of our modern or most recent Ballistics is rocket science applied to bullets. Rockets are fin stabilized, but have no paradox or bend when fired.

An arrow in some ways is not stabilized with the fletching, it is only stabilized faster. With a center shot bow, the answer is generally more spine, reducing the famous archers paradox, or bending of the projectile that is actually causing the instability. In an actual bow, where the arrow needs to bend around the bow it becomes more complex.

So you have multiple issues.

The simple answer is if you want the arrow stabilized faster, add fletching. The faster it stabilizes, the tighter the groups will be. The balance is that more fletching is more drag and weight, slower velocity.

More fletching generally means you will need more clearance at the sight window for the arrow to pass without the fletching contacting. That means less spine. You enter into an endless circle where the bow needs to be designed for the broadhead.

Then there is the root of the problem that some broad heads look really cool, and probably cut a mean hole, if only they could hit the target.

A 6 fletched flu flu will stabilize a brick tied to a stick, range becomes an issue.

I agree, we have always been "fixing the issue" but I want to explore the root casue. We hear is all the time, 'X broad heads flies exactly like a field point" well we know that is simply not possible. Or "my field points and broad heads hit exactly the same out to 100 yards". Well given drag, that is impossible. Therefore, your acceptance of deviation must be massive to consider it "the same spot". If we are talking a sheet plywood as the standard, then sure.

What this has done it made me wonder if the archery industry should provide the consumers with a "stability factor" for arrows?

So we have archers advantage and Q spine, to determine the correct spine. But imagine a program like the Berger calculator where you build your arrow, with the broadhead, and then put in your bow specs, and it will tell you if you are going to be stable.

 

[dellet]

The reason the archery industry will never have a stability factor for arrows is that a good portion of instability comes from the release.

Arrows need to be spined to within about 2-3 pounds of actual draw weight/arrow length/tip weight. Carbon Arrows are not that precise, aluminum bend, wood is unpredictable over time.

All the formulas are out there, none account for the release.

Once you get the spine to match tip weight, then you need to establish, the front of center balance point, and the fletching needs to be placed in relation to that point.

This might be close to what you are looking for. Just remember that all the science in the world won't compensate for a crappy release or a nocking point that is not correct.

http://archer1941.com/

 

[DaveTooley]

I agree, we have always been "fixing the issue" but I want to explore the root casue. We hear is all the time, 'X broad heads flies exactly like a field point" well we know that is simply not possible. Or "my field points and broad heads hit exactly the same out to 100 yards". Well given drag, that is impossible. Therefore, your acceptance of deviation must be massive to consider it "the same spot". If we are talking a sheet plywood as the standard, then sure.

What this has done it made me wonder if the archery industry should provide the consumers with a "stability factor" for arrows?

So we have archers advantage and Q spine, to determine the correct spine. But imagine a program like the Berger calculator where you build your arrow, with the broadhead, and then put in your bow specs, and it will tell you if you are going to be stable.

Are broadheads consistent enough from lot to lot or even point to point to make that practical. How do you measure the ogive on a broadhead?

 

[Bc'z]

I agree, we have always been "fixing the issue" but I want to explore the root casue. We hear is all the time, 'X broad heads flies exactly like a field point" well we know that is simply not possible. Or "my field points and broad heads hit exactly the same out to 100 yards". Well given drag, that is impossible. Therefore, your acceptance of deviation must be massive to consider it "the same spot". If we are talking a sheet plywood as the standard, then sure.

What this has done it made me wonder if the archery industry should provide the consumers with a "stability factor" for arrows?

So we have archers advantage and Q spine, to determine the correct spine. But imagine a program like the Berger calculator where you build your arrow, with the broadhead, and then put in your bow specs, and it will tell you if you are going to be stable.

Archers are always tweeking something for what ever reason tho.
When I shot indoor with a 55# Hoyt I shot way over spine, using 2613's.
I use to shoot with one of innovators of center shot bows, Don Kudlacek.

 

[Coyotefurharvester]

The old school thought, +275 fps move to a mechanical head. Also some right handed(I'm a rightly) bows spin the arrow left, so right helical is not always the best. Mark and shoot a bare shaft 3-5' to check for the "natural" spin from your bow. I like a heavy weight forward arrow and fixed blade, seems to pass through cleaner and straight. I would like to shoot 4 left hand heat vanes with my current bow, but haven't found an equipment list for fletching? Please share if you know.

 

[ebb]

bigger fletching

 

[HandgunHTR]

Adam, you need to watch the Ranch Fairy videos on YouTube regarding "Arrow Handloads". Whether you agree with his position about heavy, high FOC arrows, the discussion and steps to tune your arrow to your bow should be followed. It is amazing to me that folks will spend lots of time and $$ finding the handload that shoots great in their rifles and then just follow some "average" guide to choose their arrow spine, length, and point weight.

I have found that when I bare shaft tune my arrows, including insert, nock, spine, and point weight tuning, I have no problem getting even wide single or double bevel broadheads to fly with great stability. I am currently shooting GrizzlyStik Silver Flame 125s, which are 1.5" wide and don't have any issues with planing at all.

 

[Adam0321/0306]

The old school thought, +275 fps move to a mechanical head. Also some right handed(I'm a rightly) bows spin the arrow left, so right helical is not always the best. Mark and shoot a bare shaft 3-5' to check for the "natural" spin from your bow. I like a heavy weight forward arrow and fixed blade, seems to pass through cleaner and straight. I would like to shoot 4 left hand heat vanes with my current bow, but haven't found an equipment list for fletching? Please share if you know.

You can buy the four fletch adapters for the Bitenberger. And the new fandango fletcher is the LCA VANEMASTER PRO

 

[ebb]

I guess they probably don't even exist anymore, but I used to use 125 thunderheads never had one fail even on hogs.

 

[XTR]

My thoughts.

First, have you paper tuned? Are you shooting darts when you paper tune? If you can't get it to shoot darts paper tuned then you may need more spline. If it's flying straight 6' from the bow and it's not grouping then logic would seem to indicate that it's something between there and the target. If it's working paper tuned you're probably getting steering from the broadhead and may need to get some weighted inserts to move your center of gravity forward (gives the fletches a longer moment arm) or get bigger/more fletches.

I had a hard time getting my bow to shoot well . I went though a lot of shafts to find ones that worked for me. At 6'4" with a wing span slightly less than an NBA player I shoot long shafts from a PSE Freak. (32" pull with a Trueball release) I ended up needing 300s in Full Metal Jackets to get a good tune. (With them my bow tunes to the same with broadheads and target points.) I've been trying some Gold Tips and they are obviously a lot faster but I am not certain that 300 was enough spline, they shoot much bigger than the FMJs but I haven't had a chance to paper tune yet.

As noted by the OP, not meaning to talk down to anyone, just tossing out things to think about with some backup for folks who might not shoot bows.

 

[xswanted]

External ballistics could sort of apply to archery but there’s a lot of differences so an apples to apples comparison isn’t the best way to think about it.

There’s more info needed from you about your bow to correctly point you in the right direction......


Number one thing about getting fixed broadheads to tune is to spin test them. Screw a broad head to the arrow, point the arrow so the tip is on a hard flat surface and spin it in your fingers. If there’s no wobble at all, mark that arrow #1. If there is wobble repeat the process with other arrows until you have one that doesn’t wiggle.

Next up, are your arrows the correct spine for what you are shooting? Too stiff or especially too weak will not allow a fixed broad head to fly true to your field tips.

Cam timing........if you’re shooting a binary or hybrid cam system, are your cams to the manufacturer specs for timing? If they are not, it will be hard for broadheads to tune to your field points.

Rest Clearance........what type of rest are you shooting? If it’s a drop away are you getting adequate clearance for your choice of vanes?

Vanes......are they big enough and do you have enough?

Paper Tune it.......this can happen after all the previous questions are answered.

Walk back tune.......google this and if you want to tackle it, your broadheads will certainly Tune to your field tips when your done providing all previous items are taken care of.


To my knowledge broadheads have no “speed limit” to speak of. From my experience they get harder to tune the faster you shoot them. Little inconsistencies start to be highlighted more as you push the speed.


I’ve shot numerous types of fixed blade broadheads, some well over 300fps some way under and most of them will tune with field points with the above checklist taken care of.