# Arrow Speed Calculator on Backcountry Bowhunting



## Medwc (Nov 17, 2009)

OK, 1st,,, I don't need a lecture on arrow kinetic energy, broadhead selection or shot placement. I am trying to see what I will get from dropping grains but staying above 380 total. I just want to know if the arrow speed calculator on Backcountry Bowhunting is accurate. Here is the link if anyone wants to see. http://www.backcountrybowhunting.com/articles/tools.php
Thanks, Dan


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## alaz (Mar 8, 2009)

I have used it before, and it seems pretty close. Would like to see what others think. 
Even if it is not wholly accurate should help you find our "relative change" do to drop in arrow weight.


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## bowhunterprime (Jan 28, 2009)

I just tryed it and it was surprisingly close! But you know you can do something very similar on Microsoft Excel. I set up a spreadsheet that works like this. First, I shot my bow through a crono several times to get an accurate reading, then weighed that arrow. Puting those numbers in the formula gives me my bow's KE. Then I just change the weight of the arrow while keeping the same KE and it gives me arrow speed! I think it's a little better than the online version because you don't have to worry about a lot of possible variables. If your draw length is set to 28" is it actually 28"? Are you sure about how much weight you have on your string? If your IBO is 300-308 fps, then where does your bow fall into that range? And don't forget about drop away rests vs. whisker biscuits. If you use your own bow's KE then that is a constant (for the most part, as long as you don't change anything) for your own individual set up. -Chris


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## Medwc (Nov 17, 2009)

Well NOT having a chrono is my main problem. I don't want to cart all my stuff to a proshop to do what I am doing. I guess I could just buy a chrono. I figure if that arrow speed calculator is close that I will be close. Thanks for the info guys.
Dan


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## thunderbolt (Oct 11, 2002)

bowhunterprime said:


> I set up a spreadsheet that works like this. First, I shot my bow through a crono several times to get an accurate reading, then weighed that arrow. Puting those numbers in the formula gives me my bow's KE. Then I just change the weight of the arrow while keeping the same KE and it gives me arrow speed! I think it's a little better than the online version because you don't have to worry about a lot of possible variables.


Maybe I'm missing something, but how can you use a constant KE for different arrow weights when you have a constant draw length and weight? By changing the arrow weight, with constant draw weight and length your KE should change due to the lighter arrow...


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## Medwc (Nov 17, 2009)

Well I finally found a couple of older threads on the Arrow Speed Calculator on Backcountry Bowhunting. Most of the 30 so poster said it is pretty close so I will use it for now. On a better note... I just talked the wife into another x-mas present (a digital Pro Chrono). Hopefully she will let me have it early.
Dan


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## mdewitt71 (Jul 20, 2005)

I have 3 Chronys and this is the online calculator I use- 

http://utopiaprogramming.com/ke/KineticEnergy.html#

_I use 25 grains for the "wieght on the string" box (D-Loop, Peep, and BowJax on my Cables) and I am almost always within a couple of FPS from my Chrony. _


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## bowhunterprime (Jan 28, 2009)

thunderbolt said:


> Maybe I'm missing something, but how can you use a constant KE for different arrow weights when you have a constant draw length and weight? By changing the arrow weight, with constant draw weight and length your KE should change due to the lighter arrow...


You're thinking of the KE of a moving arrow. I'm talkin about the KE put into the arrow by the bow. When you draw a bow, you put KE into the limbs which is then transferred into the arrow on the shot. So long as you don't change anything about your set up (draw weight, draw length ect.) your bow will store and transfer the same amount of KE shot after shot with enough consistency to use to predict arrow speed when you change the weight of the arrow. Does that make more since? -Chris


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## bowhunterprime (Jan 28, 2009)

mdewitt71 said:


> I have 3 Chronys and this is the online calculator I use-
> 
> http://utopiaprogramming.com/ke/KineticEnergy.html#
> 
> _I use 25 grains for the "wieght on the string" box (D-Loop, Peep, and BowJax on my Cables) and I am almost always within a couple of FPS from my Chrony. _


Just played around with that link a little and it seemed pretty close. It works exactly the same as the Backcountry Bowhunting site.


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## Medwc (Nov 17, 2009)

:thumbs_up
Thanks bowhunterprime


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## thunderbolt (Oct 11, 2002)

bowhunterprime said:


> You're thinking of the KE of a moving arrow. I'm talkin about the KE put into the arrow by the bow. When you draw a bow, you put KE into the limbs which is then transferred into the arrow on the shot. So long as you don't change anything about your set up (draw weight, draw length ect.) your bow will store and transfer the same amount of KE shot after shot with enough consistency to use to predict arrow speed when you change the weight of the arrow. Does that make more since? -Chris


I'm pretty sure it isn't quite that simple, but Hey! if it works for you:shade:


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## OBAN (Jun 25, 2006)

bowhunterprime said:


> Just played around with that link a little and it seemed pretty close. It works exactly the same as the Backcountry Bowhunting site.


I just ran my numbers and there was 3fps and 2lb. of ke difference. Pretty close enough for me.


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## mdewitt71 (Jul 20, 2005)

bowhunterprime said:


> Just played around with that link a little and it seemed pretty close. It works exactly the same as the Backcountry Bowhunting site.


It does except the numbers seem to be closer to my bows by a few FPS...
Dunno why but, the other site gives me a lil higher speeds.


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## bowlife690 (Nov 1, 2009)

Ran my numbers and using low end IBO it was 12 FPS faster and useing high end IBO it was 20 FPS fast than the last crono. Closer than others I have used -


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## alaz (Mar 8, 2009)

What weight on string do people use for loop? I thought around 4-5grains...is that about right?
Do speed nock count as weight on string? As I wrote that it seems obviously yes, but not sure if you are supposed to count them.
Thanks.


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