Calling All Shade Tree Physicists

[Fullabull]

Make sure you test another arrow of the same weight without the insert. I agree with the rest that this will not work well and cause to much interference to the arrow, but good luck and let us know how it turns out.

[konrad]

The original concept came from considering methods for balancing lack of wall concentricity in modern carbon composite shafts and the associated rotational imbalances. A shaft’s “spline” or hard ridge along one side of the shaft indicates to me wall thickness variations. If there is in fact a wall thickness variation (or change in mass) there would also be a corresponding weight irregularity. The primary purpose of rifling and fletching is to spin the projectile so that those weight irregularities are “evened out” around an axis of rotation to produce better accuracy (more consistent flight patterns). Of course, a slightly bent shaft will produce the same poor weight distribution described above.

Are you trying to say that the granules of powder are going to balance out the weight irregularities of spline thus increasing performance, stability and accuracy?

I am not sure exactly what will happen…good, bad or indifferent.
I am saying what inspired the question(s) and what I intend to do in trying to understand what is happening.
Isn’t that the idea behind experimentation?
First there is a question.
Then there is conjecture.
Then there is experimentation followed by data collection and interpretation of the results.
Then there is further experimentation to prove the previously obtained results.

I do know that in off-road tires there is a product known as “Slime” that is shot into a tire. Then it is driven and the material gels inside the tire. Not only does it seal the tire from future punctures, it also dynamically balances the tire.

The concept of the free-flowing media traveling from the rear to the front of the arrow seemed obvious. The actual effects of that media’s travel are less than clear to me.
Hence, the coming tests.

[Boss .300 winmag]

http://hunting-washington.com/smf/index.php/topic,119572.msg1578720/topicseen.html#new

I think this is more deadly.

[TommyH]

http://hunting-washington.com/smf/index.php/topic,119572.msg1578720/topicseen.html#new

I think this is more deadly.

This might be what i was referring to, Like i said i just caught the very tail end of the comercial.

[konrad]

Buffered Arrow Follow Up Report

I received the buffer media I had planned on using in the “Buffered Arrow/Movable Weight/Extended Energy Pulse” testing.
I constructed three arrows (Easton Technical 2413 Super Slam with three 2 inch Blazers at maximum helical twist) using 145 grains of Ballistic Products Inc. Original Buffer media installed inside the shaft. The point was a 100 grain Saunders Combo point and the completed arrow weighed 535 grains.

Another three arrows were assembled without the use of the buffer media but instead used a 145 grain bullet RPS screw-in point. These “standard” shafts also weighed 535 grains.

The Easton spine calculator calls out the 2413 shaft for my 29.25 inch long shafts (nock groove to end of insert) and single cam, 61 pound draw weight Bear Truth bow with point weights up to 150 grains in weight.

When I originally was setting up this bow I had experimented extensively with point weights, nock position and rest centering to achieve the best accuracy using all of the above weighted points so I had history using the 145 grain points on these shafts in combination with my bow. At 45 yards (verified by tape measure and Bushnell Legend ARC 1200 rangefinder) the 145 grain fixed point shafts grouped about eight inches lower than my now standard point with the 100 grain points and easily maintained a four to five inch group cluster.

The shafts with the free-flowing media grouped another four inches lower than the heavy fixed points and the cluster was approaching the size of a basket ball!

After doing the shooting, seeing the results and thinking about what was happening, it occurred to me that the arrow (and the media) immediately begins deceleration upon leaving the launch platform. As such, the media is no longer held to the rear of the shaft by G-forces associated with initial acceleration. As the arrow oscillates and spins during flight, the media is shaken from its position in the rear and is thrown around the interior in completely unpredictable, chaotic and unrepeatable ways dramatically negatively affecting the fight characteristics of each arrow.

The upside of this is: I didn’t loose or damage any arrows, the arrows that I modified will be easily returned to “normal” and the neighbors’ dogs and  small children remain uninjured. At least I won’t be thinking about this problem in bed when I could be better using my time for other more profitable pursuits (like sleeping).

[Boss .300 winmag]

did you ever try one with a cylindrical slide weight?

[konrad]

No, I have not.
Perhaps a piece of Teflon???

[Boss .300 winmag]

No, I have not.
Perhaps a piece of Teflon???

heavy enough?

[konrad]

It would have to be weighed and cut to achieve the proper 145 grains. I am sure it could be done if the outer diameter of the weight could be closely matched to the inner diameter of the shaft.
I am still not seeing how the weight could be retained at the rear during flight (something I did not envision in the original imagination). Keeping it in the rear until target impact is the key to getting the secondary "impact".

While the idea has been shelved, it has yet to be discarded.

[Todd_ID]

Somewhere I've got a list of 20 bowhunting-related "good ideas" I made 15 years ago that won't work for various reasons.  I'll forward it to you if you find yourself sleeping too well in the near future.

[RadSav]

Somewhere I've got a list of 20 bowhunting-related "good ideas" I made 15 years ago that won't work for various reasons.  I'll forward it to you if you find yourself sleeping too well in the near future.

I have a bunch of them too.  Crazy to see products I designed over the past 20 years, that we've proven abslutely do not work, hit the market designed by others.

[Hunter Dug]

what about a small magnet placed in the knock to hold the slide in place till impact.

[konrad]

Yes, I was thinking the same thing.

Perhaps a small steel BB mounted at the front of the nock and a small rare earth magnet fixed to the rear of a Teflon or Delran rectangular prism shaped weight could hold the weight to the rear during draw, launch and firing. Then upon target impact, the weight would be separated from the nock and slide forward.

[SGTDuffman]

In my opinion discussing kinetic energy in relation to an arrow is much ado about nothing. Arrows kill by cutting and blood loss not by transferring kinetic energy and imparting shock like a bullet does. Arrows, by design are meant to cut through their medium doing damage as they travel. Bullets do damage and may cut as they travel too, but the bulk of their damage is done by hydrostatic shock due to kinetic energy transfer. You want a bullet to stop and impart all of its energy, you DON'T want an arrow to stop because it has imparted all of it's energy. It works for bullet because they're going several thousand feet a second and they fragment or mushroom upon impact. It doesn't work for arrows because they are going a couple hundred feet a second and don't fragment or mushroom upon impact (hopefully). The two things work on completely different mechanisms.

To that end I'm more concerned with momentum than kinetic energy. I want the arrow to continue moving and cutting. I don't necessarily care what kind of kinetic energy it would theoretically transfer if it were to stop. Maybe if I was shooting blunts for small game or something, but for broad heads, I'm putting my money on momentum. That being the case, I choose weight over speed. There are trade offs for doing this though. I have to be better with my ranging because the heavier arrows are less forgiving of ranging errors. For that reason some people prefer lighter faster arrows, and that's their choice. I'm not gonna knock anyone for choosing what they choose. Shoot what you shoot well and are comfortable using. I like the piece of mind I get from using heavier stuff. If I make a less than perfect shot (hit a bone), there's wind, or my arrow strikes a leaf or whatever on it's way, it will be less effected than a lighter arrow would. I find my setup is also considerably quieter than my dad or brothers set ups as well.

I'm shooting 620 grain arrows (Easton FMJ 340 w 75gr inserts, 10.2 grain wrap, 3-7.5gr goat tuff opti-vane fletches, and a 175gr single bevel samurai) off a 60# Diamond Rock that's a couple years old. I won't break any speed records but I'm comfortable and confident with it. I'm still working on my recurve skills, but that too shoots heavy for poundage arrows. It's a 45lb Quinn Stallion that I pull to around 47-48# and I use 545gr arrows. Won't use that hunting just because I'm not confident enough in my skills with it yet. All of human history is full of people shooting heavy wooden arrows with simple 2 blade flint tips off of handmade self bows into animals and killing them. I do find all of the physics debates and stuff over bows and arrows interesting though. It's cool seeing people trying to objectively prove or disprove different points.

You might spend some time on ArcheryReport.com. The whole page is basically just a collection of physics articles relating to all this stuff. Here's a link:

http://archeryreport.com/articles/

[konrad]

I am in complete agreement with you on using a broadhead’s cutting power to initiate hemorrhaging tissue damage. That being said, the conversation was primarily about the theoretical enhancement of that transfer of energy aiding penetration without resorting to extreme forward of center or arrows weighing much over 500 grains. Rarely, unless heavy bone is encountered, will an arrow make an immediate stop when entering game. Even then, upon entering skin, muscle and sinew energy begins to be shed from the shaft as it makes its way to that bone.

All killing projectiles rely mainly on penetration to vital organs and disruption of life support systems. It is only when discussing varmint or predator pelt harvesting that the explosive projectile really is needed (or even wanted). Contrarily to current belief, it is my contention that adequate penetration along with a suitable diameter hole extending through both sides of an animal’s vital organs is what is needed for the rapid dispatch of game in firearms too.. The current trend of homogenous expanding projectiles attempts to address the weaknesses often seen in earlier expanding type bullets (namely fragmentation, deformation and/or explosive destruction of the projectile limiting its penetration). The idea that in firearms “hydrostatic shock” alone is sufficient to humanely dispatch large (and particularly dangerous) game does not stand up to the actual results obtained in the field. Unless the central nervous system is catastrophically disrupted (i.e. Spine shot) there is no such thing as a kill from pure hydrostatic shock in an animal weighing 150 pounds or more.

Even in elephant hunting (perhaps the worst case scenario of big game hunting) the idea is to penetrate to the brain without destruction of the projectile or distortion of the projectile leading to its veering off course and missing the brain. There are a number of calibers that will penetrate to the brain of Jumbo but there are very few projectiles that will do so reliably (every single time without destruction or deformation) and produce a large enough wound channel to kill him.

I think that perhaps what I was envisioning were the benefits of a lighter arrow (500 grains) and its attendant better trajectory combined with the enhanced penetration of a heavier arrow. As in so many other things in life, there are always trade offs.
In this case, technology has yet to catch up to my imagination…but I’m still working on it.