The case for heavy arrows for penetrating bone
02-22-2003, 09:19 AM
#1
Thread Starter
Join Date: Feb 2003
Location: Murrysville PA USA
Posts: 119
The case for heavy arrows for penetrating bone
It is true that KE only increases a little bit when you switch to a heavier arrow. Based on some of Mulhaney' s bow reports doubling the weight of the arrow would lead to something like a 15% increase in KE. This is because the moving parts of the bow are moving forward at release with less velocity with the heavier arrow - there is less KE left in the bow.
The momentum increases much more, however, over 50%. And it is momentum which best represents penetration of a deer by an arrow.
Heh, heh. Newton' s second law is that F = dP/dt which means that the force multiplied by the time that that force is applied is just the change in momentum. I.e., take a case where an arrow is stopped by a bone in .2 milli-seconds, about a half inch of penetration. With KE of 60 foot pounds and a fairly light arrow traveling 300fps, this arrow exerted 2000 pounds of force on the bone for that .2 milliseconds. If I double the weight of the arrow, the KE will go up a little to say 69 foot pounds, but the momentum increases more than 50% and the arrow would have exerted 3033 pounds on the bone for this same 0.2 milliseconds.
But what' s an extra 1000 pounds among friends?
Can a light carbon arrow, with its ability to straighten out faster, make up for the inherent advantage of a heavier aluminum arrow? I don' t know. But I do know that I want the test to be done on a target that resembles the physics of a deer' s body, I don' t want it done on a target which slows down arrows by grabbing the arrows shaft which gives a huge advantage to a small diameter carbon arrow. And I want both arrows to be well tuned - probably using large helical fletchings on the aluminum arrow to make sure that it is also flying vibration free soon after leaving the bow. Using equal spine arrows is not enough, and may not even be right! - obviously arrow weight affects the spine required for a well tuned bow.
beprepn
The momentum increases much more, however, over 50%. And it is momentum which best represents penetration of a deer by an arrow.
Heh, heh. Newton' s second law is that F = dP/dt which means that the force multiplied by the time that that force is applied is just the change in momentum. I.e., take a case where an arrow is stopped by a bone in .2 milli-seconds, about a half inch of penetration. With KE of 60 foot pounds and a fairly light arrow traveling 300fps, this arrow exerted 2000 pounds of force on the bone for that .2 milliseconds. If I double the weight of the arrow, the KE will go up a little to say 69 foot pounds, but the momentum increases more than 50% and the arrow would have exerted 3033 pounds on the bone for this same 0.2 milliseconds.
But what' s an extra 1000 pounds among friends?
Can a light carbon arrow, with its ability to straighten out faster, make up for the inherent advantage of a heavier aluminum arrow? I don' t know. But I do know that I want the test to be done on a target that resembles the physics of a deer' s body, I don' t want it done on a target which slows down arrows by grabbing the arrows shaft which gives a huge advantage to a small diameter carbon arrow. And I want both arrows to be well tuned - probably using large helical fletchings on the aluminum arrow to make sure that it is also flying vibration free soon after leaving the bow. Using equal spine arrows is not enough, and may not even be right! - obviously arrow weight affects the spine required for a well tuned bow.
beprepn
02-22-2003, 09:28 AM
#2
Nontypical Buck
Join Date: Feb 2003
Location: Heaven IA USA
Posts: 2,597
RE: The case for heavy arrows for penetrating bone
Is the issue heavy arrow vs light arrow or is the issue carbon arrow vs aluminum arrow? 
I guess everyone' s definition of heavy could be a little different but certainly today a person can get some carbon arrows that carry some heft.
I guess everyone' s definition of heavy could be a little different but certainly today a person can get some carbon arrows that carry some heft.
02-22-2003, 10:05 AM
#3
Join Date: Feb 2003
Location: centerville pa. USA
Posts: 105
RE: The case for heavy arrows for penetrating bone
I won' t even get into the math of the subject but I will say this: in my vast (ha) experience of three years I have harvested two buck and both with easton acc arrows, 349' s. Both shots shattered the shoulder joint and honestly looked like an ' 06 shot. Both times the arrow shaft broke but neither deer traveled more than 30 yards.
02-22-2003, 11:12 AM
#4
Join Date: Feb 2003
Location: poughkeepsie NY USA
Posts: 24
RE: The case for heavy arrows for penetrating bone
Now that is a therory I will get behind[:-]
I have seen this test done years ago and I saw that what you are saying is correct.
I would say that the best arrow for much tougher game would be the special carbon heavy weight shafts.
A good test would be to take a hogs shoulder plate and use that for your test,large target and known for it' s ability to stop arrows.
I' d like to see how a fiberglass shaft would perform in this test.
I used to shoot fiberglass along with alot of people and we never had a problem with them,just dead slow
I have seen this test done years ago and I saw that what you are saying is correct.
I would say that the best arrow for much tougher game would be the special carbon heavy weight shafts.
A good test would be to take a hogs shoulder plate and use that for your test,large target and known for it' s ability to stop arrows.
I' d like to see how a fiberglass shaft would perform in this test.
I used to shoot fiberglass along with alot of people and we never had a problem with them,just dead slow
02-22-2003, 07:41 PM
#6
Nontypical Buck
Join Date: Feb 2003
Location: egypt
Posts: 1,994
RE: The case for heavy arrows for penetrating bone
hey Beprepn,
Do you have a copy of the Natal study. I have a copy of it and I really feel some of the findings, albeit a tad older, would or atleast might wake a few of the light arrow folks up. Then again I am not so sure it is worth your time (or mine) to even bother with them and the wars it will bring. Some folks just need to learn the hard way, its a shame though when a elk/moose (or marginal hit on any animal with a less then decently set up equipment) needs to pay for someone' s learning process when they could have done the homework before hand!
Do you have a copy of the Natal study. I have a copy of it and I really feel some of the findings, albeit a tad older, would or atleast might wake a few of the light arrow folks up. Then again I am not so sure it is worth your time (or mine) to even bother with them and the wars it will bring. Some folks just need to learn the hard way, its a shame though when a elk/moose (or marginal hit on any animal with a less then decently set up equipment) needs to pay for someone' s learning process when they could have done the homework before hand!
02-22-2003, 09:58 PM
#8
Join Date: Feb 2003
Location: Lingle WY USA
Posts: 527
RE: The case for heavy arrows for penetrating bone
I shoot 2 set-ups out of my bow....Light=395 gr. arrow going 295 and Heavy= 495 gr. arrow going 272......I' m pretty sure either will blow through an elk/moose......I' d trust either one......
02-23-2003, 06:34 AM
#9
Thread Starter
Join Date: Feb 2003
Location: Murrysville PA USA
Posts: 119
RE: The case for heavy arrows for penetrating bone
" Light" vs " heavy" is what I think is important - a " heavy" carbon might be the best of all worlds.
I think the 2 or 3 thousand pounds force, for that 0.2 milliseconds, is a reasonable number. Roughly, 60 pounds over 24 inches to accelerate the arrow agrees with 2 or 3 thousand pounds in a half inch to slow down the arrow. I.e., 24 / 0.5 * 60 is about 2 or 3 thousand. Quite impressive, over a ton even with the light arrow (although for only a very short time).
I think the 2 or 3 thousand pounds force, for that 0.2 milliseconds, is a reasonable number. Roughly, 60 pounds over 24 inches to accelerate the arrow agrees with 2 or 3 thousand pounds in a half inch to slow down the arrow. I.e., 24 / 0.5 * 60 is about 2 or 3 thousand. Quite impressive, over a ton even with the light arrow (although for only a very short time).
02-23-2003, 07:55 AM
#10
Join Date: Feb 2003
Location: Southeast PA
Posts: 242
RE: The case for heavy arrows for penetrating bone
A skinny carbon arrow also has an advantage in increasing penetration in game animals, not just foam targets. When you shoot a live animal, they twist their bodies and contract their muscles, which will ' pinch' the shaft as it passes thru the wound channel. The small diameter shaft will have less surface area to be pinched. If you think that an animal can' t move much by the time an arrow goes thru it, watch some slow motion video of a deer being shot sometime. A dead cow isn' t even a true test for arrow penetration.