# Kenetic energy???



## Phshunter10 (Nov 21, 2014)

I have a 2014 Hoyt Charger set at 65#s..27 inch draw and I'm shooting Beman bone collector MFX shafts that measure 27 1/8 inches from end of arrow to inside of nock. 100gran broad head and two inch Blazers.. Factory nicks and inserts. I'm shooting 268fps but not sure what my arrow weights. Any help is appreciated! Thanks!


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## alligood729 (Nov 22, 2014)

What spine shaft? I'm guessing a 400, based on your setup, which is what I'd shoot so we will go off that. The most common formula for figuring KE is speed x speed x weight, divided by 420,240... So......going off that, if you are shooting a 400 spine shaft....that shaft is 9gpi, at 27.25" is 245.25 grains, 100 gr head, blazers = about 18 grains, HIT insert is about 16 grains, nock is about 8 grains.....
Total arrow weight is 387.25. 
268x
268x
387.25=
27,813,844 divided by
420240 =
66.185 lbs of KE. Plenty of pop for any deer around here. 
Of course that all changes if you are shooting a different spine arrow other than a 400. But there is the formula, you can go from there!


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## Phshunter10 (Nov 22, 2014)

alligood729 said:


> What spine shaft? I'm guessing a 400, based on your setup, which is what I'd shoot so we will go off that. The most common formula for figuring KE is speed x speed x weight, divided by 420,240... So......going off that, if you are shooting a 400 spine shaft....that shaft is 9gpi, at 27.25" is 245.25 grains, 100 gr head, blazers = about 18 grains, HIT insert is about 16 grains, nock is about 8 grains.....
> Total arrow weight is 387.25.
> 268x
> 268x
> ...



That helps a lot!! I do shoot the 400 shafts. Thank you!!!

Now if I could just get a deer in bow range this season I'll be happy!


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## reylamb (Nov 22, 2014)

alligood729 said:


> What spine shaft? I'm guessing a 400, based on your setup, which is what I'd shoot so we will go off that. The most common formula for figuring KE is speed x speed x weight, divided by 420,240... So......going off that, if you are shooting a 400 spine shaft....that shaft is 9gpi, at 27.25" is 245.25 grains, 100 gr head, blazers = about 18 grains, HIT insert is about 16 grains, nock is about 8 grains.....
> Total arrow weight is 387.25.
> 268x
> 268x
> ...



That should be divide by 450240


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## alligood729 (Nov 22, 2014)

reylamb said:


> That should be divide by 450240



You are correct, I have it on my phone and still got it wrong...lol

Which comes out to be about 62lbs of KE....not 66. No big difference...


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## fishhunt05 (Mar 20, 2015)

Thanks for the formula! Im trying to keep my new bow shooting atleast 300 fps and weight of arrow at 450 grains. which would put me close to 87 lbs of ke.


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## alligood729 (Mar 23, 2015)

fishhunt05 said:


> Thanks for the formula! Im trying to keep my new bow shooting atleast 300 fps and weight of arrow at 450 grains. which would put me close to 87 lbs of ke.



Which is plenty....just remember, KE is figured with the arrow right out of the bow, it starts dropping immediately, kinda like bullets....as the arrow slows down, KE drops..but, with a 450gr arrow, the momentum of that arrow will carry the "pop" further out than a lighter arrow. I went in that direction this year, after chasing speed for the last 5 or  6 years. Went from a 340gr arrow, to a 430gr arrow. KE figures are almost exactly the same, even though I lost fps, and I know that the heavier arrow will hit harder....worth the speed to me..


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## GTHunter007 (Mar 23, 2015)

fishhunt05 said:


> Thanks for the formula! Im trying to keep my new bow shooting atleast 300 fps and weight of arrow at 450 grains. which would put me close to 87 lbs of ke.



450 grains at 300 fps is extreme KE and momentum levels.  There is not a big game animal on this continent you couldn't get two holes in every time.  

You can play with the online calculators to get the proper arrow weight that your bow will shoot at 300 fps. Just work it backwards or plug numbers and play until you get it narrowed down. Then figure out the shaft/insert/head/vane combination to meet those specs. 

Properly build the arrow with FOC and a two blade fixed head...and wow!  

I put the land sharks on my Elite setup I recently did. I have 452 grain arrows with 200 up front going 291-292 fps and the impact is unreal.  I had to buy a new target just to hold my arrows.   MO and FOC is a very real thing.  Traditional archers already know this, but apply it to today's speed bows, and wow!  I am thinking about moving to the 150 gr heads and putting the setup over 500 grains, but not sure it is necessary and I am afraid it will change my spine too much.


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## GTHunter007 (Mar 23, 2015)

alligood729 said:


> Which is plenty....just remember, KE is figured with the arrow right out of the bow, it starts dropping immediately, kinda like bullets....as the arrow slows down, KE drops..but, with a 450gr arrow, the momentum of that arrow will carry the "pop" further out than a lighter arrow. I went in that direction this year, after chasing speed for the last 5 or  6 years. Went from a 340gr arrow, to a 430gr arrow. KE figures are almost exactly the same, even though I lost fps, and I know that the heavier arrow will hit harder....worth the speed to me..



  I am pleased to read you are or have made the move to heavier arrows for hunting.  Perhaps you and others prominent around here can push the move to more lethal arrow setups.  Just 6 months ago in a thread I started here you were making the case for your lighter setup and how it was plenty sufficient.  What made you give it a try??


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## Apex Predator (Mar 27, 2015)

I've killed quite a few with 35# KE.  Just hit them in the right spot, with the right broad head.


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## alligood729 (Apr 4, 2015)

GTHunter007 said:


> I am pleased to read you are or have made the move to heavier arrows for hunting.  Perhaps you and others prominent around here can push the move to more lethal arrow setups.  Just 6 months ago in a thread I started here you were making the case for your lighter setup and how it was plenty sufficient.  What made you give it a try??



I still think that 340 gr arrow will do the job, I know so. All I was about for several  years was speed, and that magical 300fps mark, which for a short draw guy shooting 60lbs, the only way to do that was lighter arrows. I killed plenty of deer..and also shot the 125gr bipolar...but when Tim told me he was making a 165gr all steel bipolar, and asked me to try it, I said what the heck. Byron also posted a video about heavier arrows and impact points at average hunting distances. When it was all said and done, my KE figure between the 340gr arrow and the 430gr arrow was within 1 lb of each other. I lost about 15fps, but knowing that the heavier arrow will carry the "pop" a little further, I just decided to go with it. Killed one doe in Dec, and hope to pop a turkey before long.


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## coondog96 (Sep 9, 2015)

Is this formula good with what ever the draw weight is. Say my draw weight is 68 and arrow weight is 375...says my KE is 59.82...would this be the same regardless of the draw weight??


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## BigCats (Sep 9, 2015)

Been shooting heavy arrows for years love them make bow quiter they fly better and like said they will knock the heck out of something.


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## fishhunt05 (Sep 11, 2015)

coondog96 said:


> Is this formula good with what ever the draw weight is. Say my draw weight is 68 and arrow weight is 375...says my KE is 59.82...would this be the same regardless of the draw weight??



No. It depends also on the speed of the bow.


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## Ihunt (Sep 14, 2015)

fishhunt05 said:


> No. It depends also on the speed of the bow.



Close. Depends on the speed of the arrow.


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## Curvebow05 (Sep 21, 2017)

I will raise it from the dead for the sake of science. Kinetic energy is not the correct measurement for penetration.


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## Kris87 (Sep 22, 2017)

Curvebow05 said:


> I will raise it from the dead for the sake of science. Kinetic energy is not the correct measurement for penetration.



Well, it kinda is.  That and momentum.  Both use similar variables.  Not totally independent of each other.


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## Curvebow05 (Sep 22, 2017)

I like it, you brought in momentum. A 95 mph fastball has 96.5 foot pounds of kinetic energy. That is more than a lot of hunting arrows. But it won't penetrate a deer hide. Kinetic energy is a non directional energy. And all it measures is how much energy an object has due to its motion. According to the laws of physics, momentum is the correct measurement for a directional measurement of energy. It is the important part of kinetic energy for us as bowhunters. Kinetic energy is used to measure the mechanical efficiency of a bow. And yes, if you increase the arrow speed, kinetic energy of the arrow increases. Kinetic energy is not a directional force however. If you shoot two arrows with the SAME amount of kinetic energy but one carries more mass, which one will penetrate further? Another good test, a .357 magnum has about 520 foot pounds of kinetic energy. A 710 grain arrow at 110 fps has 52 lbs of kinetic energy. If you shoot each of these into a bucket of sand, the bullet stops and the arrow completely penetrates the bucket. The resistance force is greater on the faster but lighter object, meaning it stops it faster. Part of this happens because the arrow carries a much larger amount of its momentum from its mass. Where the momentum comes from is a big key. To be fair, sectional density and mechanical advantage play a part in penetration as well. What it comes down too, if you shoot the heaviest arrow possible with the broadhead that has a high mechanical advantage, while maintaining a usable trajectory for hunting, your success rate of complete penetration on game animals will increase tremendously. 
Now don't get me wrong, I like speed as much as the next guy. But I started doing a good bit of studying on this when I noticed that arrows from my 50# recurve (guessing around 170fps) penetrated as far or further into my targets than my 60# PSE XForce at 284fps. That is  over 100fps difference. The weight, and FOC of the arrows matched with my recurve are much heavier/higher than the arrows matched to my compound. Momentum carried from mass beats kinetic energy from speed all day long. I have no problem shooting through a shoulder with my recurve, but I won't do it with my much faster setup with my compound because, well, it doesn't work. 
Disclaimer:  The majority of the above posted numbers and facts are from Dr Ashby's research not mine, I am a salesman not a physicist. I learned a lot of fancy science stuff during the research and just like to share with others when it can help someone more efficiently and ethically take game animals.


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## 2bbshot (Sep 23, 2017)

Im glad you brought up Dr. Ashby the other day it was cool to refresh my memory on his findings. I used to shoot stick bows and through trial and error and people telling me that know much more about arrow penetration than me and reading works like Dr. Ashby. I took all that info from trying to figure out how to get the penetration needed from stick bows and just applied it to a compound. The results are devastating. The tread on shoulder shots just got under my skin bc Im not just reading or typing it. I have done the work and the research. I can't imagine sitting with a modern compound and wondering if your arrow is coming out. If the arrow and head selection are right the power of these new bows especially at 82lb is just incredible.


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## Curvebow05 (Sep 23, 2017)

Absolutely, I am going to set up some arrows for more testing with my compound after this season. I already shoot heavier arrows than necessary, but I am going to go for Extreme FOC and total weight and see what I can get up too. I know I have heard of people blowing through a new 3D target with certain setups and I just wanna see if I can do it with a 60# bow.


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## 2bbshot (Sep 23, 2017)

You ever played with any Simmons heads? I shot 125gr stingers on the same arrow as my 135gr tree shark and the sharks penetrate 10 in farther in a brand new big shot broadhead target all the way to the feathers. There bigger too but man it will cut.


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## Curvebow05 (Sep 23, 2017)

I haven't, they are on my list once I need to buy more though. They have too many people saying good things to be ignored.


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## Kris87 (Sep 23, 2017)

I'd agree heavier over light any day...however, I build my setups to give a good combination of speed and momentum depending on what I'm hunting and that's whitetails for me most of the time.  Deer are relatively thin bodied animals and easy to shoot through.  So I pick a combo that also allows me some error in distance judging or the animal ducking.  Otherwise, most deer hunters would just be heading to the woods with moose setups.

Good discussion.


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## Kris87 (Sep 23, 2017)

My setup now is 440gr at 290fps.  I also like to keep the speed there to help broadhead flight.  That too can't be ignored.  I've never shot a setup over 300fps in my life.


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## Curvebow05 (Sep 23, 2017)

Fixed blade broadheads get kinda funky over 295-300fps in my experience. I think 280-290fps is right where you want to be with an ideal "speedbow" setup with fixed blades.


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## 2bbshot (Sep 23, 2017)

I shoot the heaviest arrow that I can keep 270-280 fps. The big heads I like don't fly good at 300FPS. In my current bow its a 525 gr arrow. I shot a 425gr arrow and it shoot good I shot a 297 vegas round with it but its just tamer and more forgiving around 270-280. Its just what I like and my Hoyt like it more importantly.


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## 2bbshot (Sep 23, 2017)

Kris87 said:


> I'd agree heavier over light any day...however, I build my setups to give a good combination of speed and momentum depending on what I'm hunting and that's whitetails for me most of the time.  Deer are relatively thin bodied animals and easy to shoot through.  So I pick a combo that also allows me some error in distance judging or the animal ducking.  Otherwise, most deer hunters would just be heading to the woods with moose setups.
> 
> Good discussion.



Bows don't shoot flat no matter how fast they are. You have to know how far and use the correct pin or in my case move the sight. Makes no difference to the deer my tape goes to 90 yards and while I would never shoot a deer that far I shoot my target there all the time just like I did with a 425 gr arrow last year. I just feel like if I have to adjust the sight whats it matter? I put the shark in the goodies of a doe at 44 today. If UGA can win it will be a fine day!


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## 2bbshot (Sep 23, 2017)

...


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## across the river (Sep 25, 2017)

The easy way to figure it out.

https://www.realtree.com/kinetic-energy-and-momentum-calculator


Drag decreases the number due to friction a the arrow gets farther out.


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