Thin Diameter Arrows for Penetration?

UTGrad

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I don't understand how a thinner diameter arrow increases penetration. If the broadhead is cutting the wound channel, why would a thin diameter be any better than a standard diameter? Wouldn't it be the broadhead design and momentum of the arrow vs arrow shaft diameter?
 
I think maybe its less drag.I do know for a fact.Six bucks over the last 8 or 9 years,some years i dont shoot one,all taken with Easton Axis arrow behind Muzzys and all have been complete pass throughs.
The most amazing was a quartering away shot.Entrance was in front of left hip.Arrow busted shoulder on right side and kept on going.Complete pass through.The long way.40 yards was as far as he made it.
Most of these were shot with a 60lb Mathews DXT,30 draw.Shooting 256 fps.
Im sold on small diameter arrows.
 
I think the advantage of small diameter versus large diameter is mostly theoretical on game. In a 3D target it makes a difference because the foam closes up behind entry point providing friction to the shaft as it enters. On game the weight, inertia and KE I think are bigger factors. Smaller shafts like MrBro's Axis are really good balance of weight/inertia/KE. It also helps when you can shoot lights out like MrBro.
 
Hoss said:
I think the advantage of small diameter versus large diameter is mostly theoretical on game. In a 3D target it makes a difference because the foam closes up behind entry point providing friction to the shaft as it enters. On game the weight, inertia and KE I think are bigger factors. Smaller shafts like MrBro's Axis are really good balance of weight/inertia/KE. It also helps when you can shoot lights out like MrBro.

Thanks i needed a good laugh!!!! :grin:
 
I would imagine the thin diameter would have less surface area for resistance and less drag. I am not sure that they would be small enough to make a huge difference though. Physics has been a few years for me haha.
 
My guess would be less drag. But I never have heard of someone switching to a smaller diameter just for more penetration. I think your broad head has more to do with it then the diameter of the arrow.
 
I don't know if they actually allow more penetration, never given it much thought. Less surface are does kind of make sense though. I shoot easton axis fmj's. Everything I have shot has been a complete pass through with the exception of one. It was a quartering away shot where I struck the opposite shoulder and I believe that would stop most any arrow.
 
Looking at it from a physics standpoint there just has to be some difference. There definitely is a penetration difference when shooting at a target like a foam 3D target. Considering a hunting application and all things being equal, a thin diameter arrow will out penetrate a larger diameter arrow. Even though a broadhead is creating a cut channel for the arrow to pass thru, the shaft will still come in contact with tissue creating drag on the arrow, the larger arrow has more surface area so it has to have more drag, however I believe the amount of drag compared between the two will be very negligible. The type of surface of the arrow will have an effect as well, and may have a greater effect than the diameter itself�not all carbons are the same. A smaller diameter arrow also is less effected by atmospheric conditions than a larger arrow and that has been proven. I wish I had the time, money and equipment to find out exactly the difference between the two.
 
I agree there is a difference theoretically. In practical application the differenceis so miniscule as to be immeasurable. The wound channel is opened by the broadhead and the contact with the shaft would be minimal, then couple that with the lubricity of the tissues and body fluids the difference would be of no consequence. If you want to increase penetration then look other places for it. You can impact your penetration in much larger measure by doing other things. Once you are down to shaft diameter as a factor in optimizing your penetration you are pretty much there.
 
The theoretical concept of the smaller diameter shaft having greater penetration because of less frictional resistance along the shaft, following the broadhead inside the wound channel makes a lot of sense, and it's great marketing also! I have seen the ballistic gelatin tests and usually the Axis shafts does it deeper!

I've killed a bunch of critters with the Axis shaft since it came on the market several years ago! My APPLICATION with hunting with this heavier and smaller diameter hunting shaft has proven to me that it will out penetrate any other shaft I have hunted with! The Axis style shafts are some of the toughest on the market and as a bonus they really buck the wind great.

The next time you kill a deer try cutting the front shoulder off with the leg and hide attached and hang it up in front of a safe backstop. Aim right at that shoulder blade with your broadhead and shaft combo and evaluate yoyur results. Then give the Axis shaft a try!
 
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.
 
Jake47 said:
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
 
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!
 
UTGrad said:
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.
 
Jake47 said:
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.
 


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