I just came acrossed this little write up on Kinetic Energy as explained in slug feet per second rather than the old formula of foot pounds.
http://www.alaskabowhunting.com/PR/UnderstandingArrowPenetration.pdf
In using the foot pounds formula the velocity is squared rather than using it's original value.
In using the SFPS (slug feet per second) method it actually gives a more accurate value to why a slower heavier arrow penetrates better than a faster lighter one.
It makes sense to me. :rolleyes:
With all that said.....How much KE is enough, and how much KE is NOT Enough?
Can anybody put into referrence where the cut off would be for a safe KE level for taking deer sized game?
Maybe all of this has been covered before, if so please forgive my rehashing of the subject.
I don't have any idea. I would imagine it would matter a lot; where the deer was hit, the style of broadhead, how well-tuned the arrow is, how sharp the broadhead is. I do know that mid-30's generated by my set-up triggers a fatal reaction in broadside deer.
I think this chart might be useful:
http://www.huntersfriend.com/bowselection.htm#16-kineticenergy
If there is blood in the grass leading to a dead animal it was the just the right amount.
Your right large heavy sharp projectiles work very well.
Bjorn said it perfectly!
QuoteOriginally posted by NorthernCaliforniaHunter:
I think this chart might be useful:
http://www.huntersfriend.com/bowselection.htm#16-kineticenergy
That was useful, thank you.
I think J.L. Spinks was onto something in the article that I posted the link to?
It shows a better perspective of amount of KE that a heavier arrow can generate without velocity squared and just using actual velocity.
Then you get actual momentum.
I do know for a fact that when I used to shoot an 80lb. bow (which I can't do anymore) I was able to shoot a 550gr. arrow at a whopping 265fps. from my wheelie for a KE of 85.7 ft/lb. of KE.
That bow hit like Thor's Hammer!
It was by far the hardest shooting bow I have ever used. I wish I could still pull that much weight, but I can't.
So with no way to increase the speed, the only way to increase the KE is to increase arrow weight. We all know that.
Have any of you actually measured or calculated your arrow's KE? I would be happy with Bowwild's results.
Mine wouldn't be hard because I have chronographed it. With my Bear Grizzly #48 and a 510gr. arrow with a velocity of 140fps. mine only comes in at 22.2 ft.lb. of KE.
The chart shows that it's only good for small game. Should I not be using this setup then?
If not, then how do women and kids kill deer with 35-40lb. bows? Luck?
LOTS of deer-sized animals have been cleanly killed with inefficient 40-45# bows shooting 10 grains per pound cedar arrows tipped with simple two-blade heads. A deer is a very small animal, with only 12"-14" or so side-to-side.
More draw weight is better than less draw weight because of unwanted intervention of bones. But with careful shot selection and accurate placement of a good hunting arrow tipped with a good hunting broadhead, 40-45# (especially with more modern, more efficient bows) is PLENTY for deer.
Mine's around 35#KE and I feel that will put a Bear down. Hell I even read on here that a Lady used a 40# draw weight bow to drop a ELK. That's 10# lighter draw then Me and if I remember her length was shorter too.
KE and archery really dont mix. witha gun ke is more important.
in archery momentum is a bigger factor
I don't really have any doubts about killing a whitetail with my set up with a shot right square behind the shoulder.........it's the shot that goes right into the shoulder that would worry me.
No matter how hard you try to avoid it, sooner or later it will happen. And when it does, you just better hope you have enough KE to carry that broadhead into the lungs. I've learned that the hard way and a valuable lesson in KE.
But here's the thing. I can't do anything about the speed of my bow and I don't want to drop down in arrow weight to gain speed, because that's just thinking in the wrong direction.
So I guess a guy has really only got 2 choices.
1.) Shoot a heavier bow.....which hurts the shoulder more.
2.) Shoot a faster bow, more expensive.
What other way is there to get your KE up?
Increased arrow weight = increased KE
Even though velocity is squared in the formula, a heavier arrow will increase KE.
I searched the archives for posts where people had chronoed their bows with different weight arrows to illustrate this point. Here are a couple of such threads:
http://tradgang.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=1;t=061557
http://tradgang.com/noncgi/ultimatebb.php?ubb=get_topic;f=1;t=077464#000000
In one of the threads, the author even calculates the KE and you can clearly see that it goes up with the heavier arrow. On the other thread, you can calculate the KE from the results yourself.
Now, having said all that, I don't have a clue what kind of KE my setup has, and don't have any plans on finding out.
Accuracy is trump in archery-work on accuracy and shot placement-this was never about science, unless you just want to stay home.
There are vastly different opinions of what is optimum.
Something thing you may wish to consider is to maximize your arrow design and retain a similar total arrow wt.
One consideration would be to increase your arrows FOC. Getting to Ultra-EFOC may be tougher, however you should be able to get to 28% with little effort. You should be able to readily discern a penetration increase.
You will be able to discern a penetration increase.
I agree Bjorn, accuracy solves many woes with stick and string. If you can consistently hit what you are trying to hit, then you have no worries I'm sure. A well placed arrow will kill cleanly every time, and guys have been doing it for years with a set up just like mine I'm sure.
Would it be safe to say then, that if a guy sticks to the 10 gr.pr.lb. rule that he should be carrying enough Momentum, KE, Slug Power whatever you want to call it for taking just about anything he would want to hunt??
I'm actually a hair over the 10gpp rule, so I feel like there is nothing more I can do except hit the mark.
Thanks for all the help and opinions guys!
QuoteOriginally posted by sawtoothscream:
KE and archery really dont mix. witha gun ke is more important.
in archery momentum is a bigger factor
MOMENTUM is the key to penetration. It isn't really about Kinetic Energy. It doesn't take a rocket scientist to be able to see (and feel) that it takes a lot more to stop a semi trailer fully loaded traveling 40 mph than it does a hybrid sportscar doing 200 mph.
Kinetic Energy was brought into play by the compound shooters using expandable broadheads, because it does "take away" momentum to open these type broadheads.
I'll just keep on shooting my heavy arrows with loaded front ends.
Winterhawk1960
I couldn't agree with that more Don.
This response may get yanked by the mods, but I can draw a very precise conclusion relating to that very concept since I also reload my own rifle ammo.
Ballistics charts show how the KE goes up to beyond killing standard minimums using a tiny bullet just because of the high velocities they can achieve, but in the real world you know that such a tiny pill is not capable of taking large game just based on the KE it can generate with a calculator.
I think the same rules apply here, just because a light arrow can achieve a high KE value by getting it's boost from velocity doesn't mean that it would do the job when it hits an animal.
Whereas a heavy arrow at moderate speeds will do the job cleanly.
Try stabbing a soda straw through a cardboard box and watch it fold up, then try the same experiment with an unsharpened pencil and see how you are able to jam it through with no problem.
That's kinda how I picture it in my mind.
I've always been an advocate of shooting the heaviest bow and poundage that I could handle comfortably and shoot well. Then I would match an arrow to that bow and KE has never been a factor with any of my set ups.
But now that I'm older and my shoulders just can't handle that type of abuse, I'm now forced to dial it down to comfortable levels and KE or Momentum has become a real factor that I have to pay attention to.
I've come to the realization that I have to shoot a moderate poundage bow with moderate speeds, a heavy arrow which also slows down the set up even more, and keep my shots at close range.
It's hell getting old. :) :coffee:
QuoteOriginally posted by John Havard:
LOTS of deer-sized animals have been cleanly killed with inefficient 40-45# bows shooting 10 grains per pound cedar arrows tipped with simple two-blade heads. A deer is a very small animal, with only 12"-14" or so side-to-side.
More draw weight is better than less draw weight because of unwanted intervention of bones. But with careful shot selection and accurate placement of a good hunting arrow tipped with a good hunting broadhead, 40-45# (especially with more modern, more efficient bows) is PLENTY for deer.
Yep....worth another read...
QuoteOriginally posted by sawtoothscream:
KE and archery really dont mix. witha gun ke is more important.
in archery momentum is a bigger factor
This one as well....
Not to go all engineer here but I have to say, KE is virtually irrelevant to penetration. It is a measure of the energy stored in the arrow in flight. It tells you nothing about the penetration of the arrow after impact. Momentum tells you a lot more about arrrow penetration.
Bjorn nailed it on the head. Put a sharp stick in the kill zone and you just made meat.
Agree wholeheartedly that KE isn't something to obsess about. For sure not something that I consider. But, it is interesting to me to keep in mind that whatever setup you are shooting, the heavier arrow will yield more KE--I guess I find it interesting that a formula usually touted by "speed" guys is also a formula that corroborataes what longbow and recurve shooters have been saying forever--use a "reasonably" heavy arrow and you are better off.
SEMO--one other thing you could look at is to find a more efficient bow at "XX" pounds if you really want to add more "umph" to your setup.
QuoteOriginally posted by CG:
Agree wholeheartedly that KE isn't something to obsess about. For sure not something that I consider. But, it is interesting to me to keep in mind that whatever setup you are shooting, the heavier arrow will yield more KE--I guess I find it interesting that a formula usually touted by "speed" guys is also a formula that corroborataes what longbow and recurve shooters have been saying forever--use a "reasonably" heavy arrow and you are better off.
SEMO--one other thing you could look at is to find a more efficient bow at "XX" pounds if you really want to add more "umph" to your setup.
Yes I have been thinking about that for quite awhile now. I know there are more modern designs and bow makers right here on Trad gang that have faster/more efficient bows at roughly the same poundage as what I'm shooting now. I just don't have the funds to consider one at the moment, but hopefully before next season I will.
I could shoot more than my #48lb. Grizzly, so I'm not stuck at that draw weight. I think I could go at least as high as 55# and still shoot comfortably, at least with lots of practice I know that I could work into it in no time at all.
Ran my setup through the calculator and it saws I have 43.18 ft lbs. of KE...whewww, just made it into the large game animal category...haha
I did some calculations a few months back using a calculator that estimates "point blank" velocity with different arrow weights based on my bow's setup. For the sake of doing the numbers I pretended each arrow was tuned to my bow. If I remember correctly the graph was a U shape where there was actually two arrow weights with different velocities and weights that had fairly equal KE. One light arrow and one heavy arrow respectively. Of course momentum sides with the heavier arrow when comparing the two. And yes the heavier arrows eventually showed a climb in KE. I also did some calculations regarding impact force, momentum, elastic collisions, and so-on. Unfortunately when I just looked for the spreadsheet it seems to be missing. It's a very interesting topic. Being new to traditional archery I have been very interested in maximizing the chance of making a kill if I shoot too far forward and hit bone coupled with having an arrow with the least amount of arc out to 30 yards even though 25 yards is my goal for personal effective hunting range. If I find the spreadsheet I will share it with whomever cares to see it.
if youre that intent on shooting a heavy arrow , why not just shoot an even faster bow , with an even heavier arrow...
sounds like you need a wheelie or two...
-hov
I think KE is a fair way to compare bows, and a lousy way to predict penetration.
We got here because compound sales groups could show big numbers due to the importance of velocity in the KE formula.
QuoteOriginally posted by hova:
if youre that intent on shooting a heavy arrow , why not just shoot an even faster bow , with an even heavier arrow...
sounds like you need a wheelie or two...
-hov
I think you missed the point Hov?
There are faster trad bows over other trad bows, so one could maximize the potential of a quicker more efficient trad bow design and yes shoot a heavier arrow or just stick with the wt. your using. Then gain a higher momentum or ke whichever way you decide to measure it and minimize the probability of falling short of doing the deed if the worst should happen, encountering heavy bone ie shoulder blade.
I just wanted some of the other guys opinions on the subject to see how they determine their own KE, Momentum, Slug ft.per.sec. ect.