Brian_Mc

How much of the arrow length are you supposed to measure? From the nock center or the arrow end? To the end of the tip or to the end of the arrow (insert)?

The reason I ask is that it appears that BowJackson calculates it basically without the tip added in. I think that The Archery Program is that way also.

This measurement can make a huge difference on FOC when you use a longer broadhead (NAP Thunderhead) versus a short one (Rocket Steelhead).

CargoF16

Use the entire arrow length, field tip/broadhead included.

Cargo

ChefKell

Measure from tip to tip. Divide it by 2 to find the center.

AB Bow Hunter

What is FOC & how do I measure it, & why would I want to measure it
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Brian_Mc

FOC stands for Front of Center. You care, mainly, because of fixed blade broadhead flight. It's basically physics. The vanes use leverage based upon where the balance point is.

The &quot;experts&quot; say that you should maintain between 9 and 12% front of center balance point. Some others say 10 to 15, so practically, I try to make it to 10%.

Go to www.bowjackson.com and look under FOC. There's a calculator and some pictures to show what to measure. I've found that the calculators can be misleading, so you probably want to measure yourself. The formula is FOC = 100 * (Balance point)/(arrow mid-point) where the balance point is the distance from the arrow mid-point to the actual balance point, versus from the nock.

Hope this helps. Do a search for FOC and you'll find many threads discussing it!

CargoF16

AB, think of FOC as a measure of stability. An arrow with a high FOC (15%) would have a heavy nose and tend to have good broadhead flight characteristics (all things being equal). The drawback to this is decreased range. Arrows with high FOC tend to drop off quicker at ranges of 30+yards. Some 3D aces shoot FOCs of 7% because this gives the arrow a very flat trajectory. The nose it light so the arrow carries well at range however if that arrow had a broadhead instead of a field tip it would more than likely wander significantly. Hope this helps.

Cargo

Strut&Rut

Bowjackson measures to the tip of the point. The archer's program I have been told measures to the tip of the arrow shaft.

You can do the mathematics without either, and calculate both methods.

First, measure from the nock seat to the shaft tip. Next, balance the arrow on a pencil, and mark the balance point (with the tip on). Now measure from the nock to the balance point. Divide the balance distance by the overall length, subtract 0.5 and multiply by 100. This will give you the FOC %. To change the calculations, simply measure the entire arrow to the broadhead/fieldpoint tip.

By not measuring the entire tip (broadhead or fieldpoint), you obviously will increase the FOC. The reason for not measuring the point is due to the relationship between spine and FOC. The weight of the nose affects spine---hence a fieldpoint and a Zwickey might both weigh 145 grains, but they are very different in length. However, the arrow's FOC balance point will still be the same, as the nose weight is kept constant (at least in physical theory---in actuality, there may be very minor discrepancies---like 1/16 of an inch).

The general rule of thumb is target FOC = 8-12%, hunting FOC 11-15%---a happy medium is anywhere from 10-12 %. The higher FOC, as indicated earlier, will result in loss of trajectory as yardage increases. However, a higher FOC will also result in increased penetration and KE at shorter distances, where most hunting shots are taken.

S&R

PS&gt; There's also an article on this in the October Peterson's Bowhunting magazine.

AB Bow Hunter

By my cal. I am @ 7.1% FOC. <img src=icon_smile_shock.gif border=0 align=middle> I haven't even bought broadheads yet.<img src=icon_smile_sad.gif border=0 align=middle> I used the measuring method @ Bow Jackson.

I am @ 71 lbs, 30&quot; draw, 3-60 ACC's, 75 grain tip, 3&quot; vanes. My arrow length is 30.75&quot;, with field point, the bal. point is 13.5&quot;.

Brian_Mc

AB, I think you proved my point again. Plugging your info into Bo Jackson's specific page for ACC's (http://home.att.net/~sajackson/arrow_acc.html) yeilds an FOC of 5.5%, but your measured FOC is 7.1%, which by the way, I'm not sure where you measured from to get 13.5&quot; balance point. Why? I believe its because the ACC page only measures to the end of the arrow, not the end of the tip as shown on the measurements page. (http://home.att.net/~sajackson/archery9.html) I don't mean to look a gift horse in the mouth because Jackson's doesn't cost anything, but it's kinda confusing!

Is there a specific reason you went with 75 grain tips? If you go up to 100's, you'd probably get a much better FOC. But frankly, I believe that if your field tips and broadheads group well, then don't worry about FOC. If your groups big (&gt;2 or so inches @ 20 yards), then look at FOC. In my case, I put EZE EYE crests on and it took my FOC far enough out to make a difference.