Kinetic energy and momentum A good read

[2chucks2]

Recently I have studying the effects of broadheads on game in an effort to select a new broadhead to go with the new bow and carbon shafts I bought. In my search I came across some very interesting reading that has really opened my eyes. I have been shooting arrows for more than 30 years. I have taken 31 deer with a bow but I learned a lot from reading these articles. The first is a paper by Dr. Ed Ashby. This guy is the ultimate authority on arrow lethality. After reading his paper I will now completely change my approach for selecting a broadhead. I have for a long time thought that Kinetic energy was the a very important indicator of the killing force of a broadhead/arrow combination. I was way off. KE is nothing more than the potential for the energy you have put into your arrow. Momentum is a far better indicator of the arrows ability to do the work we want it to. Please read this article.
www.datakey.com.au/steve1/Momentum.pdf

These next sites helped to make things more clear to me.
www.alaskafrontierarchery.com/Articles.html

www.booneman.com/_terminalarrow.php

And finally this site will help you know what your bow is doing for you. It will save you a lot of math as well. Just plug in your data and see just how well your setup performs. From all the articles I have read over time. Most folks agree that the Minimum momentum for a white tailed deer would be around .30 Lbs/sec . I tend to agree with that.
home.att.net/%7Esajackson/ballistics.html

[BT]

Yes...I have Bo Jacksons site in the theory's section.
The calculator is a handy devise

Thanks for the other links!....Good Stuff

As to Ashby....Although he is indeed an authority....I consider some of his work to be suspect and certainly thin by comparison since the time of his work in Africa.

The theory of Momentum for instance.

He is correct in part but certainly not in total as to his theory on the weight that the Momentum theory holds.

At the time of Ashby's report the quality of equipment and the efficiency of the same was far below what is common today.

This efficiency translates K.E. in a far different manner than what Ashby personally saw for himself.

As you will see on Bo Jackson...the heavier shaft compared to the lighter shaft does not hold in practice , with only a thin marginal victory be given to the heavier shaft.

Having said that...the heavier shaft is all around better since it has a huge advantage at ranges beyond the effective range of the bow.

Bleed off in energy generally happens at 25yrds to 30 yrds. and the Momentum factor (at that point) will indeed begin to show serious gains in penetration as distances continue on from there.

The effective point of real gain is generally 10yrds. past the point of the flat trajectory or first pin.

Now with all of this in mind....are you going to be shooting at a distance (regularly) where you will need to rely on the Momentum factor?.

[BT]

o.k.....

lets say you have a 100# bag of grain dropped on you from 3' above and a 80# bag of grain dropped on you from 6' above.

Which one would be more likely to have you in the back of an ambulance?

[mahly]

Actually.In MY findings, and most others, the heavier arrow will have MORE KE. (check bowjackson.com for comparisons)
The heavier arrow DOES do much better at VERY long ranges...simply because the aerodynamic drag at lower speeds (on an arrow with similar KE) is lower due to the lower velocity.
the heavier arrow (out of the same bow) will have more KE at 1", and even a larger margin at 100yards. the lighter arrow will never have more KE.
As long as the KE is close, it really doesn't matter if it's heavy or light. KE is the best gauge of penetration potential.

As for the stone and bowling ball. You would MUCH rather get hit with the stone than the bowling ball. Even though its going slow enough to catch, it has the KE to knock your head REALLY hard. Throw the stone at some bowling pins LOL

Again, as far as ARCHERY is concerned, do what it takes to HIT the target! If that means going to a lighter arrow to reduce errors in range judgement...DO IT! If it means going to a heavier arrow to gain stability...DO IT. A given bow will launch different weights of arrows at very similar amounts of KE. You will get much better results #1 hitting the target, and #2 using a head that penetrates well (thank GOD for this site!) than worrying about KE or Momentum.
NOTE: This was not meant to sound argumentative... text rarely conveys your true emotion. I mean no malice to anyone (after re-reading my reply, I can see where someone could have thought that I was saying "I'm right, and you're wrong"Just disagreeing)

[BT]

haha .... no offense taken.

My position is that if you have one bow with a given potential , you cannot gain the same K.E. with the heavier arrow due to the fact that it will lose speed otherwise , K.E.

Lets take a bow that shoots an arrow that weights 300 grains at 312 fps

Now take that same bow and put a 500gr. arrow to it and the speed drops to 242fps
(Bow efficiency's being relative)

The 300 grn arrow has a K.E of 65 #

The 500 grn. arrow has a K.E. of 65#

The difference is that at long ranges the heavier arrow wins because of momentum.

In the short (as it pertains to archery) the faster allows a smaller point of aim and therefore less chance of error until it drops out.

[Greg Krause]

I have to say that with all the arrow swithching I have done this year, I did get SLIGHTLY better KE with a heavier arrow. I had 1# more KE with a 488 grain arrow over my 370grain arrow. I was also shooting over 30fps slower with the heavy arrow. I'm still over 70#'s KE so I'd take the flatter arrow anyday. If I was very borderline with KE, which would limit my shot distance to start, I think I'd go with a heavier arrow.

All of this being said, I have never shot a deer with an arrow lighter than 415 grains. I will have first hand experience this season. Last year my bow wasn't properly tuned and a 425 grain arrow with a little over 60 #'s KE blew through the boiler room of a buck at 47yds and EXPLODED on the rocks on the other side. I don't have any worries about a 370 grain arrow with over 70#'s KE out of a well tuned bow.

[BT]

I have been hunting for three years with a 300gr. arrow out of a 60# bow and have never lacked for pass throughs at any distance on any animal.

Even shot a Buffalo @ 35yrds. through both shoulders and the arrow made it entirely through.

It dropped on the ground on exit....but it went through

[mahly]

I have pretty much never found that a 500gn arrow will have the same KE as a 300gn arrow shot from the same bow. Perhaps the efficiency is greater with the heavier arrow. But it should be close enough not to make a difference.
Being archers, no one will mind if I split hairs on this...but I don't think that just because the heavier arrow has more momentum, it keeps it's energy longer. It's due to the fact that at a low speed, it has the same KE, at that lower speed, the force of the arrow going through the atmosphere is less than on the lighter arrow going faster. Twice as fast doesn't mean twice the resistance...it's much greater than that.
That said, being that you have a well tuned bow, and a competent archer behind it... While SOME would scream that your using too light of an arrow, I know better. that 300gn arrow is just fine as long as it has some energy, and you hit what your aiming at.

Admittedly, I have been nit picking a bit. I think we both agree that a very fast, light arrow (that hits the target) kills JUST as dead as a slow, heavy arrow (that hits the SAME target)

I read some of the articles at the beginning of the thread... Now THAT is some screwy logic, and REALLY twisted science in some of those links. my favorite is that KE (being the only measure was weight and speed) could be spread out all over through vibration and oscillation, but momentum (being the only measure was weight and speed) could ONLY be used to gauge penetration!!! They twist the definitions of each around until they get what they want out of it.
My 2nd favorite is comparing the penetration of a .45 lead (soft) slug with that of an arrow with a sharp head on it to PROOVE that KE isn't as good as momentum LOL !!! NOTHING like comparing apples to Volkswagens!!!

[BT]

LMAO! Apples to volkswagons!.........Thats classic!

My 2nd favorite is comparing the penetration of a .45 lead (soft) slug with that of an arrow with a sharp head on it to PROOVE that KE isn't as good as momentum LOL !!! NOTHING like comparing apples to Volkswagens!!!

I have seen that before and I always get a chuckle out of it

[2chucks2]

I started this thread and I see it has grown in my absence.