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#3497356 - 12/12/13 10:25 AM Re: Thin Diameter Arrows for Penetration? [Re: Hoss]
Jake47
Spike


Registered: 07/30/13
Posts: 61
Loc: Brentwood

Offline
Here is my "physics" take on it:

Beman ICS Hunter
400
8.4 GPR
0.293" dia
0.92 sq. in/in surface area

Easton Axis FMJ
400
10.2 GPR
.262" dia
0.82 sq. in/in surface area

Based upon these two arrows there are two things that pop out (assuming arrow speed is identical).

First, the FMJ has 11% less surface area than the ICS. Regardless of the material the arrows are shot through, the FMJ would have 11% less friction acting upon it to slow it down. However, I would tend to agree with Hoss that with the lubrication of the body fluids and fats in an animal, that this frictional number would be relatively small and would not likely slow the ICS enough to not get a pass through.

Second, the FMJ weighs 21.4% more than the ICS. This will lead to a 21.4% increase in kinetic energy, which we all know leads to better penetration. I would guess that this is the main reason for better penetration with a FMJ arrow.

However, if the two arrows being compared were the same weight then that would throw out the kinetic energy factor. That leaves only one thing that I can think of, shaft flexibility.

While a cylindrical object, such as an arrow shaft, usually gets stronger as the diameter increases, it is possible that the narrower shaft has a thicker sidewall dimension. If this is the case, the moment of inertia of the narrower shaft might be more than that of the thicker shaft. A larger moment of inertia means less deflection of the shaft when shot and upon impact.

A simple way to think about this is imagine trying to push a sharpened pencil from the eraser end through a taught piece of paper. Goes through pretty easy, right. Now take a piece of sharpened uncooked spaghetti and try and push it through the paper from the back end. I would imagine that spaghetti stick would bend quite a bit before penetrating the paper or breaking. While this might not be the best analogy, I think it at least provides an image for understanding how shaft flexibility may play a role in it.

I would like to note that I have shot ICS Hunters for 10+ years now. My bow is the same age as the arrows and is only shooting about 250 FPS. In all the deer I have shot with it, I can only remember 3 that didn't pass through. 1 I spined, 1 I buried it in his front shoulder (didn't find, but was shot by gun hunters on our farm 1 month later with the arrow still there), and 1 that I think buried in his offside shoulder but never found to confirm.

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#3497451 - 12/12/13 11:45 AM Re: Thin Diameter Arrows for Penetration? [Re: Jake47]
UTGrad
14 Point


Registered: 12/01/07
Posts: 8898
Loc: Franklin, TN

content Online
[quote=Jake47]Here is my "physics" take on it:

Beman ICS Hunter
400
8.4 GPR
0.293" dia
0.92 sq. in/in surface area

Easton Axis FMJ
400
10.2 GPR
.262" dia
0.82 sq. in/in surface area

Based upon these two arrows there are two things that pop out (assuming arrow speed is identical).

First, the FMJ has 11% less surface area than the ICS. Regardless of the material the arrows are shot through, the FMJ would have 11% less friction acting upon it to slow it down. However, I would tend to agree with Hoss that with the lubrication of the body fluids and fats in an animal, that this frictional number would be relatively small and would not likely slow the ICS enough to not get a pass through.

Second, the FMJ weighs 21.4% more than the ICS. This will lead to a 21.4% increase in kinetic energy, which we all know leads to better penetration. I would guess that this is the main reason for better penetration with a FMJ arrow.

However, if the two arrows being compared were the same weight then that would throw out the kinetic energy factor. That leaves only one thing that I can think of, shaft flexibility.

While a cylindrical object, such as an arrow shaft, usually gets stronger as the diameter increases, it is possible that the narrower shaft has a thicker sidewall dimension. If this is the case, the moment of inertia of the narrower shaft might be more than that of the thicker shaft. A larger moment of inertia means less deflection of the shaft when shot and upon impact.

A simple way to think about this is imagine trying to push a sharpened pencil from the eraser end through a taught piece of paper. Goes through pretty easy, right. Now take a piece of sharpened uncooked spaghetti and try and push it through the paper from the back end. I would imagine that spaghetti stick would bend quite a bit before penetrating the paper or breaking. While this might not be the best analogy, I think it at least provides an image for understanding how shaft flexibility may play a role in it.

I would like to note that I have shot ICS Hunters for 10+ years now. My bow is the same age as the arrows and is only shooting about 250 FPS. In all the deer I have shot with it, I can only remember 3 that didn't pass through. 1 I spined, 1 I buried it in his front shoulder (didn't find, but was shot by gun hunters on our farm 1 month later with the arrow still there), and 1 that I think buried in his offside shoulder but never found to confirm. [/quote

Awesome thanks

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#3497572 - 12/12/13 01:16 PM Re: Thin Diameter Arrows for Penetration? [Re: UTGrad]
Jake47
Spike


Registered: 07/30/13
Posts: 61
Loc: Brentwood

Offline
To investigate the Kinetic energy a little farther:

Beman ICS
8.4 gpi
100 gr broadhead
30" arrow

Total wt = 30*8.4+100=352gr

FMJ
10.2 gpi
100 gr broadhead
30" arrow

Total wt= 30*10.2+100=406 gr

Neither total weight accounts for fletching/nocks/inserts, etc. but will serve as a base point.

At 275 fps the Kinetic Energies are as follows:
Beman KE=59.12 ft*lbs
FMJ KE=68.19 ft*lbs

So at the same speed, the FMJ produces 15.3% more energy to bust through an animal. If the FMJ shaft is in fact stiffer, then less energy is lost in flexing. I think that the increased KE with the possibility of a stiffer shaft for the FMJ is the main reason for the better penetration.

If we look at it such that the KE is equal between the two arrows, the ICS would still be shooting 275 fps, while the FMJ would be shooting 256 fps. In this situation, the KE would equal 59.12 ft*lbs for each arrow. If arrow penetration was still witnessed to be better with the FMJ arrow, then I think I would be more inclined to say that the shaft is stiffer. Thus less energy is lost due to flexure of the shaft upon impact and more is available to punch through a deer, elk, target, whatever!

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#3497897 - 12/12/13 04:47 PM Re: Thin Diameter Arrows for Penetration? [Re: Jake47]
UTGrad
14 Point


Registered: 12/01/07
Posts: 8898
Loc: Franklin, TN

content Online
I just don't buy the Easton Injexion craze. Why buy an arrow that limits broadhead selection in hopes for better penetration?
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#3497905 - 12/12/13 04:51 PM Re: Thin Diameter Arrows for Penetration? [Re: UTGrad]
knightrider
12 Point


Registered: 09/27/10
Posts: 6124
Loc: tn

Offline
on thin whitetail bones how much more penetration do you need? thru a rib, thru the lungs, out the other rib, in the dirt
_________________________
behold the lamb of GOD,when he nocks please answer it may be your last chance!!!!
happy hunters against armchair biology!!!!
SAVAGE ARMS!!!!

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#3497978 - 12/12/13 05:45 PM Re: Thin Diameter Arrows for Penetration? [Re: knightrider]
UTGrad
14 Point


Registered: 12/01/07
Posts: 8898
Loc: Franklin, TN

content Online
Gold Tip Prohunter, XT, Expedition Hunter has killed a lot of deer.
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#3498401 - 12/12/13 11:26 PM Re: Thin Diameter Arrows for Penetration? [Re: UTGrad]
deerhunter10
10 Point


Registered: 08/21/12
Posts: 3372
Loc: maury county tn

Offline
 Originally Posted By: UTGrad
I just don't buy the Easton Injexion craze. Why buy an arrow that limits broadhead selection in hopes for better penetration?


x2 they are coming out with more broad heads for them but it still turns me off for them.
_________________________
GO VOLS






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#3498404 - 12/12/13 11:53 PM Re: Thin Diameter Arrows for Penetration? [Re: deerhunter10]
Hoss
TnDeer Old Timer
8 Point


Registered: 02/14/00
Posts: 1459
Loc: Hendersonville , TN

Offline
Analysis Paralysis.
_________________________
"The future of bowhunting depends on effective education"..... Bill Wadsworth

A mere shadow of the man I once was... Me!

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#3498406 - 12/13/13 12:16 AM Re: Thin Diameter Arrows for Penetration? [Re: Jake47]
Hoss
TnDeer Old Timer
8 Point


Registered: 02/14/00
Posts: 1459
Loc: Hendersonville , TN

Offline
 Originally Posted By: Jake47
Here is my "physics" take on it:

Beman ICS Hunter
8.4 GPR
0.293" dia
0.92 sq. in/in surface area

Easton Axis FMJ
10.2 GPR
.262" dia
0.82 sq. in/in surface area

Based upon these two arrows there are two things that pop out (assuming arrow speed is identical).

First, the FMJ has 11% less surface area than the ICS. Regardless of the material the arrows are shot through, the FMJ would have 11% less friction acting upon it to slow it down. However, I would tend to agree with Hoss that with the lubrication of the body fluids and fats in an animal, that this frictional number would be relatively small and would not likely slow the ICS enough to not get a pass through.

Second, the FMJ weighs 21.4% more than the ICS. This will lead to a 21.4% increase in kinetic energy, which we all know leads to better penetration. I would guess that this is the main reason for better penetration with a FMJ arrow.

However, if the two arrows being compared were the same weight then that would throw out the kinetic energy factor. That leaves only one thing that I can think of, shaft flexibility.

While a cylindrical object, such as an arrow shaft, usually gets stronger as the diameter increases, it is possible that the narrower shaft has a thicker sidewall dimension. If this is the case, the moment of inertia of the narrower shaft might be more than that of the thicker shaft. A larger moment of inertia means less deflection of the shaft when shot and upon impact.

A simple way to think about this is imagine trying to push a sharpened pencil from the eraser end through a taught piece of paper. Goes through pretty easy, right. Now take a piece of sharpened uncooked spaghetti and try and push it through the paper from the back end. I would imagine that spaghetti stick would bend quite a bit before penetrating the paper or breaking. While this might not be the best analogy, I think it at least provides an image for understanding how shaft flexibility may play a role in it.

I would like to note that I have shot ICS Hunters for 10+ years now. My bow is the same age as the arrows and is only shooting about 250 FPS. In all the deer I have shot with it, I can only remember 3 that didn't pass through. 1 I spined, 1 I buried it in his front shoulder (didn't find, but was shot by gun hunters on our farm 1 month later with the arrow still there), and 1 that I think buried in his offside shoulder but never found to confirm.


WOW!!
Okay you seem to allude to the fact that the KE will not be the same because of the weight differences of the shaft types mentioned. The speeds will differ as well (assuming you are shooting from the same setup) The heavier arrow will be slower than the lighter one. So already this means you are comparing apples to oranges. Second the pencil and and spaghetti analagy loses steam because of the differences in the spine of the two, the spine of the two arrows in question are identical (400). So that goes out the window. The increased shaft diameter goes out without a common wall thickness,AND in the case of carbon arrows a comparison of the carbon weave (a major factor in carbon arrow spine).
So if the two arrows you want to compare have (in Theory) the same weight, and speed shot from the same bow and are shot into a deer, elk, moose or bear with the same 1 1/2 inch broadhead attached to the front of it the diameter of the shaft will make very little difference to the amount of penetration.
Again, at the risk of sounding redundant, if you are looking for the shaft diameter to determine the maximum amount of penetration, then you have wayyyyyy too much time on your hands. But hey no skin off my nose, Postulate away!!!
So says the guy that shoots a 31.5 inch 2317 aluminum arrow at 260 fps with a 125grain Thunderhead out of a 78lb bow from the year 2000. Penetration has never been a concern for me.

By the way I actually agree with Mr.Bro and I believe the Axis arrows are some great arrows.
_________________________
"The future of bowhunting depends on effective education"..... Bill Wadsworth

A mere shadow of the man I once was... Me!

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#3498562 - 12/13/13 06:42 AM Re: Thin Diameter Arrows for Penetration? [Re: Hoss]
Mr.Bro
10 Point


Registered: 08/02/09
Posts: 2809
Loc: Hendersonville Tn.

Offline
I think i'm getting a headache.
_________________________
Fight Organized Crime-Reelect No one.

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