FOC Formula....?

[TradPaul]

Hey All,

  Does anyone have the formula to figure extreme FOC on a given set up. Thanks.

Paul.

[kyhuntertoo]

http://home.att.net/~sajackson/archery.html

[Rob DiStefano]

FOC via manual calculations          :D    

Use a finger to find the balance point of yer arrow.

BAL = the distance from the groove in the arrow nock to the balance point.

LENGTH = the distance from the groove in the arrow nock to the back of the arrow point.

HALF = LENGTH divided by 2

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Here's the FOC formula ...

(BAL minus HALF) times (100 divided by LENGTH)

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Example ...

29" = arrow LENGTH

14.5" = arrow length HALF

22" = BALance point

22 - 14.5 = 7.5

100 / 29 = 3.448

7.5 x 3.448 = 25.86

25.86% FOC

   

[KSdan]

Can you tell me gain what a good FOC should be?

[Terry Green]

I've shot around 18% for over 2 decades....its worked for me from bunnies to buffalo.

[Rob DiStefano]

Originally posted by Terry Green:
I've shot around 18% for over 2 decades....its worked for me from bunnies to buffalo.

Terry makes a very valid and apropos point.

No one needs rocket science to hunt with trad tackle - what trad gear to use isn't as important as how ya use it.  The final equation to solve is the hunt itself, which has less to do with bows 'n' arras and way more to do with huntin' savvy.

[Lashbow]

12% is Normal
15-19% is heavy
19 25 is Extreme

I dont know if that is teh text book standard
but pretty close

[KSdan]

Thanks-that really helps. . . I have been in the extreme. Interesting. . .

So I am trying for 12+gr/# while above 12% foc-  is that right??

[Rob DiStefano]

Originally posted by KSdan:
Thanks-that really helps. . . I have been in the extreme. Interesting. . .

So I am trying for 12+gr/# while above 12% foc-  is that right??

There are no FOC rules.  Just experiment and see what works best for ya.  

There ARE gpp rules for stickbows, and the 10gpp is pretty standard (meaning, holding 50# at yer draw length should equate to at least a 500 grain arra).

The further below 10gpp, the more you can suffer hand shock and possible limb & riser issues because unused limb/release energy is lost back to the riser and limbs.  I think going below 9gpp begins to put the bow and you at harm's risk.

The higher gpp ya use, the better for the limb energy transfer to the arra, more flight stability, and aids penetration.  The down side, if any, is a slower arra.  "Slow" can be a relative term at 10-20 yards, and have a much more significant meaning at 25-35 yards.  

I like my arras with extreme 25%-30% FOC and a good 12gpp weight.  I feel that the heavy up front weight adds a good measure of stability to arra flight, as well as penetration.  This is what works best for me in a huntin' arra.  YMMV.  Experiment!

[KSdan]

Thanks a lot.  I have been shooting 550-600gr with 20-25% FOC.  Just wondering if that sounded right.  Been shooting this way for 20 years.  Though concern for FOC is newer to me.

[KSdan]

Oops. . . 550-600 with 55# curve and now 57# LB.

[TradPaul]

Thanks Rob/Terry, I'm sitting pretty much right at 20% and am getting awesome arrow flight and impact.
Length: 30"
Balance" 21"

 My FOC= 19.998%

My actual arrow is as follows
30" shaft, with CE 150's shooting a 47 pound Bruin Recurve. 250 grain field point. My draw is at 28.25". 560 Grain total weight...Just right    

Thanks again Guys.


Paul.

[Rob DiStefano]

Here's a link to an Excel file I built that'll give ya FOC and GPP ...

 Excel .xls file

 Enterprise Excel .xlsx file