Hey Guys, Need a little advice. I just built up some arrows for my Crocodile. The bow is 68" and according to my scale, 55# at my draw of about 28 1/2". My arrows are 29" to BOP and average about 585 grains with 160 gr. point. I used Byron Ferguson's method from Become The Arrow and my FOC comes out to 21%. They seem to shoot fine and from 10 to 15 yards are sticking straight in the target. Is this much FOC unusual?

If Memory serves me, according to Ashby, Extreme FOC starts around 28%-32%...then above that you hit UFOC. (ultra).

what you have is just good ole decent FOC

My foc is around that.  Alot of guys are shootin even higher foc.

Based on the data provided, the arrow is not likely near 21% FOC.

Note:-- Extreme FOC- > 19% to <30%

Thanks. According to Ferguson the max should be 20 %. I should have taken into account what year that book was written.

Avoid extremes -----------

IMO, words to live by

Friend is right on both accounts.  Your arrow is probably near 13% FOC, or less.

He could have 21% if he has an adapter in addition to the point. Here is one of my set-ups:


FOC   
ARROW   length   28.5
   shaft+feathers+nock wt      240
   separate insert weight?      30
   rope weight/tube weight      
   adapter weight?      100
   point weight      135
   total arrow weight      505
   balance length      21.12
      FOC %   24.11

Granted, I'm using a shorter arrow, but not all that much. Note, my point weight is 135, but I have a 100 grain adapter and a 30 grain arrow insert for a total of 265 grains up front. I was using a Beman ICS Bowhunter 500 in the above example. These shoot like darts and blow through whitetails easily.

BTW: I used an FOC calculator that works in a spreadsheet to calculate the FOC in this example.

I must have done some wrong calculating. If length is 29" to BOP, balance is 18 1/2" from bottom of nock groove, what is my FOC?

% FOC=  (( Dist. Knock throat to balance point  )   - 0.50)  X  100
                ((                Shaft Length                         )    


((18.5/29) – 0.50) X 100 = 13.8%

I'm at 21% FOC and my total arrow weight is 555 gr. But I'm using 100 grain brass inserts. I get great results with this setup(see my sig. below).

According to Dr Ashby there are a several categories of forward of center (FOC) used to describe the percentage of weight forward an arrow has.
   Normal FOC = 0 percent to 12 percent
   High FOC= 12 percent to 19 percent
   Extreme FOC =19 percent to 30 percent
   Ultra Extreme FOC = more than 30 percent
According to the information you  provided I would agree with FRIEND your present foc is 13.79
You can  find a easy calculator for FOC at
http://tuffhead.com/education/formulas_FOC.html

If your arrows shoot good, then you're good to go....  no sense getting into some stuff about what Ferguson likes or what Ashby likes.  That arrow is what you like.  Leave it at that.

No issues with EFOC if you tune your bow properly and have a fair form:


30 meters (33 yards !!!) robin hood with 300 gr point on 50 gr brass insert and 10,6 gpi shaft (gold tip big game 100):

Tried the "triple Robin" but too much on the left        

 

 

Quote% FOC= (( Dist. Knock throat to balance point ) - 0.50) X 100
(( Shaft Length )

I could swear you are suppose to measure from the end of the nock not the throat of it. We are measuring mass weight from end to end. Not that a grain or two is really going to mean anything though.
????

Thanks for link to the calculator Joe, it makes it easy for us mathematically challenged types. I always wondered what my FOC was, now I know.

I measure from inside nock throat to BOP