Hey all...this may seem like a stupid question but stick with me. I recently switched to carbons from 2413 XX75 aluminums. I'm now shooting the Vapor Blackhawk 4000's ....Anyways my main question is would to much FOC cause the arrow to drop more...shooting 125 gr tips my FOC is around 13%...if I drop back to 75 grain tips my FOC is 9.1 and I see alot flatter arrow flight. I know some of this my be due to the increased speed gained by dropping 50 grains of arrow weight. I wouldn't be too worried but I'm trying to make up my mind if i would be better off going out and buying some 75 grain broadheads...I have a 6 pack of 100 grainers and a 6 pack of 115's but I was wanting to get the input of some of you with more technical expierence before I went out and bought another pack of broadheads....
Thanks

Carpn,

Nothing wrong with 13% or 9.1% FOC!!!! The main consideration should be hows your arrowspine after you change. Do the arrows fly well? I don't see any problem using what you already have in inventory if the arrows fly and group well.



Aim Hard!

For my arrows, I won't go very much below 10% FOC with broadheads. I've shot as high as 15% on wood arrows with 180 grain heads and they did great out to 25 yards, but did start nosediving around 30. In my opinion, it's worse to go too light with FOC than it is to go heavy because too little nose weight will let the arrow 'float' with poor stability.

You'd probably be okay at 9%, but it it was me, there would be 100 grain heads on those arrows to get closer to 10%.

Arrow flight is good with tips from 75 to 125...there is just way more arrow drop with the 125's...probably 8-10 inches difference at 30 yds...If I use the 75's I could site in one pin to be dead on in the low 20's and use it from close in all the way out to 30 where its only about 2 inches low if that....I'm gonna try and tweek things though and see how well the 100 grainers shoot before I buy anymore.

If you haven't read Rangeball's 'arrow weight revelations' thread, you need to. Good info in it bearing on this issue of yours. Playing around with the sight-in distance, you'd be able to shoot one pin out to 30 yards with any of those heads you're talking about.

Interesting little tidbit...

In Peterson's Bowhunting, there are two good articles concerning arrows, fletchings, spine, FOC and broadheads.

The author of the one article first points out that you must use the properly spined arrows for your bow. Second, that FOC is drastically ignored within the hunting community. He recommends 8-10% for target shooting and 12-15% for hunting. He actually computes the FOC by balancing the shaft of the arrow (he recommends on a pencil) to find the center of balance. Measure from the where the string sits in the nock to where the aluminum arrow meets the insert (to where the actual head screws in on carbons). Next measure from the same point on the nock to the center balance, as derived by your "pencil test". Divide the shorter center length by the total length, deduct 0.5 and multiply by 100 for FOC % (or in mathematical terms, ACL/AL - 0.5 * 100). Of course this is by memory alone, but I just roughly calculated my FOC, so I think this is the correct equation.

Now what is interesting here, is by Jackson's site calculations my arrows had an FOC of 11.5%. By the author's computations for actual FOC, my calculations indicated 14.3%. I shoot flat out to 30 yards, two pins---1 for 25 and under and 1 for 25-40---with little drop.

Good article, check it out.

I just responded to this ?? because I found a large disparity between the two systems (~3% in actual Vs. site computed FOC) so thought I would pass this along. In essence, if you have merely relied on a site calculation you may be actually shooting a much higher FOC than you think.

S&R

Strut& Rut,that is also how I figure foc,like the author of the article.This also the same as Easton says you should do it.I do believe that Easton reccomends going to the center of the nock,where the string sits.


I beleive this to be correct and my archer program will figure the same as I.This hasn't failed me yet.


I understand Sajackson's theory behind the way he does it but I'm not sure that I agree.We all have the right to our opinions,though.

Jackson's method of calculating FOC includes the tip into the length of the arrow which in my opinion is more correct. Since the total arrow length includes the tip, why would it not be included into the FOC computation?

Aim Hard!

Since you ask I will reply.

The correct mathematical way to figure foc would be to use the whole point.On the other hand,the balance point of the shaft is usually in reference along with spine,and the carbon or aluminum doesn't have any idea how long the weight is up front it just reacts to the weight.This is strictly my opinion and that of some major arrow manufacturers.

Let me add this.If we are talking about a head that is very long,then maybe we need to account for it to some degree in figuring spine and foc.I really don't know because I have never used extremely long heads.Maybe the real answer is somewhere in the middle.

Edited by - tfox on 09/18/2002 16:23:41

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