Calling All Shade Tree Physicists

[konrad]

Calling all Shade Tree Physicists


I was lying in bed one morning not too long ago and thinking about arrows. OK, all you folks about to make snide remarks about poking things and other suggestive comments, here is the place to get it out of your systems.

At any rate, I was thinking about arrows, the physics involved in impact drivers and energy transfer pulse/time intervals…OK, you can make a couple of more jokes here too. You won’t be the first (or last) to make fun of me…and I began to wonder about an experiment with the following conditions:

1.   With a “standard” arrow weight of 500 grains striking a target at a “standard” velocity of 250 fps obtain an energy transfer pulse length as a “base line”. In other words, obtain a measurement of the length of time the arrow actually delivers its energy to the target.
2.   Then, as a starting point, construct an arrow with a free floating, internal weight, occupying the rear one third of the inside of the arrow weighing 50 grains as a starting point.
3.   The Forward of Center (FOC) of the rear-weighted shaft would be 15% FOC.
4.   Then, the test arrow would be shot into the target at the same initial velocity of 250 fps and the energy transfer impulse time would be measured again.

My belief is that the weighted arrow’s transfer time would occur over a more prolonged period than that of the un-weighted shaft. If so, the effect would be similar to an impact driver, assisting in penetration due to the act of the internal weight transferring its energy to the tip of the arrow. In effect hitting a “double tap” upon impact.

My question is: Should I spend valuable sack time in more productive pursuits or might I be onto something?

Thanks,
K

[boneaddict]

Your arrow will probably hit fletching first, or do summersaults in mid air, but other than that....

[Todd_ID]

Since when do physics enter the witchery of archery? 

The impact of the arrow is such a violent situation that the arrow flexes as much or more than it does when fired from the bow.  Your weight would rattle around and maybe vibrate down the shaft, but I doubt it would be anything close to the double tap you are looking for.

With 50 grains in the rear, then you'd have to have a huge broadhead to get your 15% FOC.  A large weight and large broadhead only leaves you with a light shaft weight to get your 500 grain target, so spine would become an issue.  (However, putting the weight on the rear would help to negate this a little.)

The momentum of a 50 grain weight flying forward inside a 450 grain arrow would be equal to the momentum of a 500 grain arrow.

Even if you could get the double tap you are looking for, the result would be negligible increases in penetration ability due to needing to overcome static friction (which is much higher than dynamic, or sliding, friction).  You'd still be better off with just a 10% increase in arrow weight.  In this case 450+50 does not equal 500.

Overcoming friction (as the definition of arrow penetration) isn't dependent upon time.  It's a function of mass, surface area, velocity, and coefficient of friction.  The only ways to increase the penetration of an arrow are to increase the mass (heavy), decrease the surface area (skinny), increase the velocity (fast), or decrease the coefficient of friction (slick and flying straight).  Since friction is calculated with velocity squared, increasing the velocity provides incrementally smaller gains in penetration.  The aluminum arrows of 25 years ago penetrated as good as or better than what we see today with carbon because they were heavy, slow, straight and smooth.  Today's bows are light years beyond what we shot back then, but we still killed critters just fine.  Put an aluminum arrow in today's bows, and you're far beyond what we used to blow through critters with.

An impact gun doesn't work by extending the time of impulse; it works by delivering high torque blows in rapid enough succession that the user does not feel the full torque and thus can hang onto the tool.

Now, if your floating weight would happen to be a BB, it could be used to strike a primer inside that could set off a charge of powder, and then you'd have a more effective killing machine; I think the state would frown on this, however.

[KFhunter]

I'm digging the flying bangstick idea, I could really rambo it up 

[konrad]

Perhaps I wasn’t clear in the original post. Both of the completed arrows must be of the same weight.

The internal weight I am going to use in testing is shot shell buffering media.
It is non-hygroscopic, light spherical plastic, free-flowing and does not stick to anything. I currently have some on order and as yet do not have a good idea of its density in grains per cc. As it happens, I use alloy shafts in a modern bow and the internal finish is mirror bright and smooth. While it (the buffer media) will easily be moved to the rear of the shaft by tilting the arrow up, as soon as deceleration due to target contact is encountered, it will begin moving toward the front in one extended (hopefully) “pulse”.

My primary issue (as I have already decided to proceed with experimentation assuming I can get appropriate weights before running out of internal space) has been in the manner in which quantitative data is to be collected. I have imagined a crude method would be the use of ballistic gelatin or perhaps clay. First shooting a “solid” arrow into the medium and then shooting into a fresh block with the movable weight arrow, both tipped with the Saunders Combo-point. One sees the use of ballistic gelatin in firearms testing as a standard media for projectile/load experimentation. It would seem to me that the same media should give excellent results at least giving an “apples to apples” comparison.

Look at it this way, I could be drinking whiskey and picking fights with other drunks or still asleep!

[chrisb]

Doesn't this "prolonged" energy transfer only have real impact if the arrow doesn't go all the way through and exit?

[jaymark6655]

Isn't that the stuff that sticks to everything due to static and is really light.  On testing shoot each arrow 20 or more times then measure depth of penatration, then see if there is any difference in the averages.  What about using some really small lead shot or powder like that used in dead blow hammers?

[KFhunter]

I think you'd loose about 90% of your pulse effect from the buffer media into the walls of your arrow.  The first little bit would slam to the front of the arrow then as the rest slammed into the leading media the forces would be diverted to the walls of your arrow shaft.

You need a solid slug to slide back and forth.

[JPhelps]

Energy equation from physics would state that no more energy can be created once the arrow was in flight.  Only deduction of energy (wind resistance, gravity, hitting flesh or bone, etc...).  You would also add in friction loss from the sliding action which would contribute to worse penetration.

You want an arrow as heavy as possible flying as fast as possible that is flying straight.

[yajsab]

I think right when the arrow leaves the string, the arrow will grab the free floating weight making it flying backward.  Hopefully the knock will not explode or come loose.  If everything is intact, I think the motion of the free weight will reduce the arrow speed to some degrees.  My .02.

[Todd_ID]

Better glue your nocks in well for a downhill shot. 

Sounds like a fun project, but I don't think you'll beat the laws of physics.  Jason is right: energy cannot be created after the arrow leaves the bow.  Time has no part in figuring penetration (friction).  Watch some super slow motion videos on youtube of arrows when they hit a target to see the horizontal forces you have to overcome to get your weight to slide forward.  I predict the arrow will hum on the shot, penetrate just shy of equally with the solid 500 grain arrow, and hum on the impact.  The hum is energy lost.

[JPhelps]

The arrow will be spinning in flight.  The RAM would also spin with the shaft.  So in order for it to slide freely it couldn't be to tight.

I am imagining a wobbly arrow because of the loose ram?

[BULLBLASTER]

I was under the impression that a deadblow hammer is to eliminate the hammer bouncing back up off the hammered item or surface. Arrows usually won't bounce off a soft tissue. I also agree with Jason in that all arrows of the same weight shot the same speed will have the same energy when leaving the bow. Arrow broadhead and fletching differences will change drag and downrange energy. I did an experiment a number of years ago regarding arrow speed. I filled a fat shaft arrow completely full of 125 grain screw in tips and shot from my 70 lb x force. On impack with the target the tips inside bulged against the shaft walls and created cracks all over the shaft.
On another note have you ever seen anyone knocked their inserts out using a drill bit inside the shaft and swinging the arrow? I think your weight inside the shaft would just knock the insert out inside the target. 

[coachcw]

Now this is a good waste of your brain power . a 420 grain arrow at 300 fps will blow right through a elk at 50 yards what else do you need . try curing cancer with that nogan instead.

[TommyH]

I seen somthing similar on a hunting channel just a couple days ago?

[Boss .300 winmag]

I seen somthing similar on a hunting channel just a couple days ago?

And what was the outcome?

[TommyH]

I seen somthing similar on a hunting channel just a couple days ago?

And what was the outcome?

It was just a advertisment i think, for a new arrow with a sliding weight in it, I tried to rewind it so i could check it out but I had just turned to that channel so it wouldnt let me rewind far enough. I dont recall the name of the company but i dont think i had ever heard of them.

[jechicdr]

Arrow tube separated by a thin glass divider. In back pressurized gas and a projectile that on impact would shatter the barrier, releasing the gas.  In front a vacuum that would suck the projectile to the front of the arrow.  So instead of relying on the momentum of the arrow to drive the impact on the head, the pressure difference in the arrow would drive the impact.  Of course the recoil might slow the arrow initially, unless you blew out the back of the arrow as well so the escaping gas would also propel your arrow forward to counteract it.  Or just make the entire arrow filled with compressed gas that blew out the back end of the arrow on impact.  I'm a genius.

[Smokey Bear]

Just thinking out loud here. . .

We don't talk much about "knock down" power with a bow, but wouldn't you want the strongest impulse all at once?  NASCAR has crumple zones and safer barriers to absorb the tremendous force and lengthen the time of the impulse, thus protecting the internal organs of the drivers.  Although static friction is very very small considering the razor sharp broadheads we use, I still don't want to "overcome" it twice! 

There has also been talk of how the arrow will fly. . . but just maybe the arrow would fly straighter near impact, with a weight shift to the tip???  I don't know??? 

I applaude questions like this, it's how the next innovations in archery will be born!

   

[RadSav]

jechicdr, ToddID and JPhelps all make an interrelated point that is an important one.  For the RAM to move free within the shaft there will be chatter or rattle robbing energy at a very rapid rate.  If the RAM fits snug within the internal space of the shaft there will be created upon impact an equal vacuum/pressure on each side of the RAM making it only moveable to a point of the amount of compression allowed by the gas within the shaft. (this will happen regardless, but at a much higher extreme if the RAM gives little room for gas to escape around it's surface)   Assuming that impact of the projectile is at point blank and the impact immediately stops the progression of travel of the shaft and the 300 fps 50 grain RAM is then 100% energized for forward momentum the FPE of that RAM completely friction free is about 10 pounds.  Not nearly enough to collapse the vacuum chamber and explode the pressure chamber enough to make any additional impact force against the solid impenetrable object. 

Fact is arrow travel at target is going to be at a speed less than point blank, there is no such thing as 100% friction free travel,  immediate stoppage or transfer of energy of an arrow on impact with ballistic gelatin is not likely, and arrow oscillations will not allow for a tight fitting RAM to travel unobstructed down the length of a shaft externally or internally,  the vibration created will only rob more of the projectiles energy than will be left if and when the RAM actually makes contact with the front of the stationary projectile.   Whewww!

No double tap of any useful benefit if you are able to achieve one at all.  A micro diameter 50 grain tungsten needle might have a chance, but I like your chances of drawing a Washington State goat raffle tag much better than seeing any measurable benefit from even that.  Especially since the "tap" against the back end of the arrow upon release will be at a greater velocity than the "tap" on the front end upon impact.  Thus imparting more decrease in velocity/energy upon the release than you will gain upon impact.  As Todd eluded to in his original post impact of a slower moving 450 grain arrow followed by a second impact of a slower 50 grain RAM would result in less penetration than a solid 500 grain arrow traveling at full speed with no RAM at all (450+50=<500).  And as JPhelps eluded to the energy of a two part arrow traveling at X-speed has the same amount of energy as a two part arrow traveling at the same X-speed.  You can not gain more energy only lose energy due to the additional friction.

[Hunter Dug]

If the object within the shaft was lightly secured to the rear of the arrow, this would stop any rattling during flight.  Upon impact the object breaks free and travels the length of the arrow and slams into the insert, and broadhead.  A small hole in the rear of the nock would have to be drilled to let gases excape from the arrow as the object transfers from the rear of the arrow to the front.  The only issues would be FOC for flight, securing the object within the shaft until impact, and keeping the insert, and broadhead connected to the arrow once the object hit them.

[KFhunter]

or

the arrow shaft in a complete vacuum

[Hunter Dug]

you could prevent vacum by drilling a thru hole in the slug that was inserted within the shaft.

[konrad]

As I said earlier, I will be using a powdered shot shell buffer media in the first tests…if I can obtain a usable weight and still have free space within the shaft.
The fine buffer media will be free to distribute itself within the shaft by way of centrifugal and inertial forces. My objective is to tilt the shaft upward slightly during the draw cycle to move the media to the rear of the shaft. If the media is not placed in the same relative position prior to each shot, more or less energy would be absorbed by moving the media on launch thereby producing (I believe) variances in launch velocity.

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.

We shall see…

[RadSav]

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?

[RadSav]

At times sleep comes easier if you make the leap of faith that sometimes a stick and a string simply shoots another stick.  And leave it at that

[coachcw]

on a different note. what if bow manufacturs listed maximum ke. insted of ibo. for instance what weight arrow creates maximum ke some bows it may be 500 grains other may be six hundred .

[RadSav]

on a different note. what if bow manufacturs listed maximum ke. insted of ibo. for instance what weight arrow creates maximum ke some bows it may be 500 grains other may be six hundred .

Manufacturers would never do such a thing instead of IBO.  Perhaps some would add it to the list, but I would assume most would find it time and effort without return.  KE means quite little in the realm of killing or bow efficiency and thus creates as much confusion as any real life benefit would give them or the bowhunter.  It's why AMO standard speed calculations are never used anymore since the adoption of IBO speed standards. 

Those IBO speed standards, which are easily and often manipulated, serve a single purpose - to sell bows!  Nothing in archery creates as much emotional involvement and aides in the selling of completely backward designed, meaningless advances and poor shootability than does speed.  Creating such a standard has assured that sooner rather than later an archer will feel the need to upgrade.  Not from a lack of success, not from a lack of accuracy and not from a lack of shootability, but due to a growing discontent for numbers.  It assures that bows will not be handed down from generation to generation as would be the case with a classic firearm.  But discarded like trash as would be last years Windows operating system and the computer that only thinks at a rate 1,000 times faster than the human mind.

It is presented to the archery community as a standards of measure.  And while true within the wide spread variables of the AMO, ATA and IBO guidelines manufacturers use it more as a sales tool than any viable standards procedure.  A KE standard of measure would surely be as filled with wide interpretation and manipulation as speed squared.  Without the added benefit of using it to drive sales and emotionally charge a happy archer into discontent.

[WDFW Hates ME!!!]

I think the only difference you will see is different points of impact, due to the different weight distribution of the arrows. 500 grain arrow shot next to another 500 grain arrow but 1 arrow is 450 grains with a 50 grain slider still weighs in at 500 grains and same available energy. You shouldn't lose any to friction as it still weighs in at 500 grains.
I think you would lose accuracy as your media inside your shaft would have to be in the same position at release every time or it would hammer back at release.

[Todd_ID]

Slow Motion Archery Hoyt UltraElite Wendy EX-F1

That is a modern bow and aluminum arrow.  Carbon arrows are worse for the vibration you'll find at impact: worse in that they will be less predictable.

[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.

[Todd_ID]

In this case, technology has yet to catch up to my imagination…but I’m still working on it.

If you can dream it, then the technology exists.

If your simple final goal is lightweight arrow penetration, then you have 2 main directions to accomplish it: reduce friction or better arrow flight (less horizontal losses at impact).  Design a tiny diameter arrow that has a teflon coating and perfect flight with the broadhead, and you'll reach your goal.

[SGTDuffman]

You may be able to someday theoretically achieve the results with technology but that doesn't mean you'd be able to use it. In this case because of state laws governing minimum arrows weights etc. It's also a bit counterproductive to use lighter and lighter projectiles with a bow. As the projectile gets lighter, the bow converts less of it's stored energy to the arrow because it encounter less resistance from it. You'll end up getting more of the bows energy as vibration and noise, and less and less of it actually propelling the arrow any faster.

I noticed that with the heavier arrows too. Just for kicks I shot some of my old arrows over a chronograph with some of the heavier stuff I shoot now. As you'd expect the lighter arrows were faster, but any increases in bow strength or draw gave the lighter arrow less advantage. The relationship between arrow weight and the energy extracted from the bow isn't linear. I shot both arrows from the same bow on the same day from the same distance over the same chrono. The only change I made was turning my draw weight up 5#. That change netted me an extra 10 fps from the heavy arrow and an extra 5 fps from the light arrow. Those gains may sound insignificant, but for something only going a couple hundred feet a second 10 fps is a 5% gain in speed. Would I gain 10 more fps if I turned it up another 5#? I dunno. I didn't do it. I only turned it up to 65#. I'd still expect to gain more on the heavy arrow though, though I can't say with any degree of certainty how much. It's kind of fun to play around with that stuff though.

The point I was making about hydrostatic shock is that it does more damage to surrounding tissues than the actual bullet does. The point would still be to hit the vital organs, but with a bullet there is more leeway because of the shock. You can destroy arteries and tissues you didn't hit, with an arrow that isn't really the case. That's also not to say the shock is so great that you can shoot a deer in the ass and kill him, but you could disrupt the central nervous system without actually hitting it. Passing a bullet near the spine would likely be sufficient to paralyze the animal. I think of cavitation and the like along the same lines of how a torpedo works. The goal of a torpedo is not to detonate on impact with a vessel, it is to impact below the vessel, and create a cavity or a pressure wave that will break the vessel in half. While putting a hole in a boat is good, snapping it in half is better. It's the same with a bullet. Ideally, you put a hole in what you want, but as a corollary, you also get a huge pressure wave that does as much or more damage than just the bullet hole.

Like anything else, kinetics and momentum and all this other stuff related to it, like the bows, arrows, points, etc is all a compromise. You pick what meets the needs you set for it. The best bet is a compromise between the weight and speed of the projectile. Which is what it you've done. I thought about tuning mine back down a bit to get some more range and minimize the range estimation, but it isn't really necessary for me. I like how the bow shoots and it's extremely quiet. Though I was worried at first if I was going way too heavy. I went from around 400 grains to 620 grains. Haha, aside from the 7th pin on my Spot Hogg being just for looks, I have no regrets.

It just seems lately that everyone is solely concerned with more speed. I'm not saying that because of anyone on here or any of this conversation though, just a general observation. Nobody touts their bow for being quiet or light or efficient, but everyone talks about how fast it is. It seems like pending some sort of major technological break through, speed has gone about as far as it's going to go with the knowledge and materials currently available. It seems like 350-360fps is pretty much it. There are some one off custom operations or guys tweaking stuff or shooting super light arrows that got up around 600fps a couple times, but production bows seem to have hit the wall in what they're capable of safely doing. Now technology seems to be focusing more on the arrows. Making arrows stiffer, lighter, stronger, and smaller in diameter.