FOC?

[Jeremiah P]

I'm currently shooting easton axis nano arrows in 340, 9.5 gpi. I checked the foc and found it was quite a bit lower than I wanted. So my question is, will the foc get better if I go to a heavier arrow? Been looking at the full metal jackets which are .8 gpi heavier. Just worried I will have issues tuning my broadheads. Thanks

[sebek556]

what grain broadhead are you using? also are the arrows wraped?

[mtbiker]

Going to a heavier arrow and not increasing the weight of the broadhead will *reduce* your FOC.  You need to remove weight from the rear and/or increase the weight of the broadhead to get more FOC.

[Jeremiah P]

100 grain and no wrap. Was thinking about weighted inserts in front but not sure, might just have use heavier tips

[jgrimes]

Going to a heavier arrow and not increasing the weight of the broadhead will *reduce* your FOC.  You need to remove weight from the rear and/or increase the weight of the broadhead to get more FOC.

Shouldn't reduce it at all if the nock and vanes on the back end match your current setup and if the arrow is cut to the same length. I would just add weight to your front end and try and get in the % range you're trying to achieve.

[mtbiker]

Going to a heavier arrow and not increasing the weight of the broadhead will *reduce* your FOC.  You need to remove weight from the rear and/or increase the weight of the broadhead to get more FOC.

Shouldn't reduce it at all if the nock and vanes on the back end match your current setup and if the arrow is cut to the same length. I would just add weight to your front end and try and get in the % range you're trying to achieve.

Going to a heavier arrow while maintaining the same length and components will absolutely reduce  the FOC.  Not by much, but it will reduce it.  I've experienced this first hand and all the arrow calculator apps out there will confirm it.  Try the Gold Tip arrow builder tool on their site with the same arrow length and components, but different arrows  (e.g. XT 5575 vs. XT 7595).

Anyway, if more FOC is desired, go to a 125 gr point, but be aware that it may have a noticeable  influence  on the spine, depending bow setup.

[buckfvr]

So...what is your FOC, and is there any indications that it is too low ?

[jgrimes]

Going to a heavier arrow and not increasing the weight of the broadhead will *reduce* your FOC.  You need to remove weight from the rear and/or increase the weight of the broadhead to get more FOC.

Shouldn't reduce it at all if the nock and vanes on the back end match your current setup and if the arrow is cut to the same length. I would just add weight to your front end and try and get in the % range you're trying to achieve.

Going to a heavier arrow while maintaining the same length and components will absolutely reduce  the FOC.  Not by much, but it will reduce it.  I've experienced this first hand and all the arrow calculator apps out there will confirm it.  Try the Gold Tip arrow builder tool on their site with the same arrow length and components, but different arrows  (e.g. XT 5575 vs. XT 7595).

Anyway, if more FOC is desired, go to a 125 gr point, but be aware that it may have a noticeable  influence  on the spine, depending bow setup.

I'll explain my understanding of FOC and you let me know if we're on the same page (not tryin' to start an argument, just like discussing these things  )

The weight on an arrow shaft is dispersed evenly no matter the gpi. Two shafts cut to the exact same length will balance at the same point as their center of gravity is the same. Adding the exact same components (BH or point, insert, bushing, nock, vanes) from one arrow to another (assuming they will work on the new arrow) will maintain the same FOC. Only adding to the front end or removing from the back end will change either arrows FOC.

[Button Nubbs]

how do they shoot would be my question.

[jgrimes]

how do they shoot would be my question.

Having more weight on the front of your arrow should stabilize your arrow better. You should notice better arrow flight with an arrow that has a higher FOC. What % FOC is your current setup?

[newred]

FOC is all about weight distribution. Take two arrows one slightly hevier than the other and put the same point on both and the percentage of weight distribution at the front of the arrow will be different. If you want better FOC then you will need a heavier point or more weight up front. upping the arrow weight without changing anything will decrease your FOC.

[mtbiker]

I'll explain my understanding of FOC and you let me know if we're on the same page (not tryin' to start an argument, just like discussing these things  )

The weight on an arrow shaft is dispersed evenly no matter the gpi. Two shafts cut to the exact same length will balance at the same point as their center of gravity is the same. Adding the exact same components (BH or point, insert, bushing, nock, vanes) from one arrow to another (assuming they will work on the new arrow) will maintain the same FOC. Only adding to the front end or removing from the back end will change either arrows FOC.

Sure, no worries.  It's not obvious at first glance.  So, let me put it this way...  And my apologies if I don't make sense.  Google is your friend.      So, the more FOC, the closer the point/front of arrow will be to the balance point.  Or the greater the distance from the center of the arrow to the balance point.  There needs to be more shaft or weight hanging off the back of balance point to compensate for the heavier front, which is good.  Focusing on the shaft, say 40% of the shaft is forward of the balance point.  If the weight of the shaft is increased, like going from 8.6 GPI to 8.9 GPI, 60% of that weight gain difference will be put at the back end of the balance point.  Remember there is a 60/40 weight distribution with regards to the shaft.  In order to achieve a new balance point the arrow will need to be moved forward from the current balance point which will reduce the FOC (i.e. the balance point to the center of the arrow is reduced).

As mention the reduction is very small.  Especially, going from 8.6. to 8.9, but there is a reduction.  Also, if the shaft has a weight forward design the reduction will less, but again still small.

[Fullabull]

Front of Center Balance: go to this link and read about FOC towards the lower section: http://www.huntersfriend.com/carbon_arrows/hunting_arrows_selection_guide_chapter_4.htm

"If you've ever played a friendly game of darts, you've surely noticed that the dart is designed so that it's heavy in the front, and light in the back.  If the dart were weighted the opposite way, with the tail being heavier than the tip, it would literally spin around and hit the target tail-first.  Obviously the ballistics of a dart and an arrow are a bit different, but the underlying concept is similar.  A projectile's flight is most stable when most of the projectile's mass is positioned Front (or Forward) of Center [FOC].  As such, an arrow should be heavier in the front than in the back.  But how much?  Where's the "perfect" balance point? 

This is another hotly debated issue among archery enthusiasts.  In fact, some of the self-proclaimed chat board gurus seem intent on beating the FOC issue to death.  So before we get into this, we need a quick reality checkpoint.  If your FOC is really really out of whack, it's an issue.  But don't spend too much time splitting hairs about whether your FOC should be 9% or 10%.  If your FOC is reasonable (7-15%), your arrows will function as they should.  And don't assume that the mathematical average (11%) of the recommended 7-15% range is somehow the best score.  It doesn't work that way.  The ballistic physics for FOC include some rather elastic variables that make finding an "mathematically optimal" FOC very difficult to declare and prove.  To make matters worse, we even see a variation in how FOC itself is calculated (some include the tip of the arrow in the length measurement, some stick with the AMO arrow length measurement).  So don't pull out your scientific calculator on the FOC issue.  It's not necessary.  Just choose a reasonable value and move on.

Fortunately, most common arrow components tend to yield finished arrows well within the recommended 7-15% FOC range.  The only real danger of slipping off the FOC precipice is if you use really heavy fletching and super-lightweight target nibbs, or if you choose small light fletching and a jumbo tip weight (or a heavy brass insert).  For common arrows with basic vanes or feathers, aluminum inserts, and 85-125 grain tips, chances are your FOC will come out just fine.     

With all that said, it is generally believed that an arrow with a high FOC will fly well, but with premature loss of trajectory (nose-diving).  While an arrow with a very low FOC will hold its trajectory better, but it will fly erratically.  So again, another trade-off for you to consider.

If you balanced a standard raw arrow shaft (no components), the balance point would be the middle of the shaft (0% FOC).  But since tips and inserts at the front of the arrow are usually heavier than the fletching and nock at the tail, most finished arrows balance somewhere just forward of the middle.  So computing FOC is pretty basic.  In the example on the left, the 30" long arrow has balance point that is 3" forward of the arrow's actual center (15").  So its FOC is 3/30 or 10% of the total arrow length forward of the arrow's physical center.  Example 2:  If a 28" arrow balanced 2" forward of its physical center, you would compute the FOC as 2/28, or 7.1%.  Easy!

So when you order your custom arrows, keep FOC in mind.  If you choose heavy 5" vanes and an anorexic 50 grain tip, you'll likely have an FOC that is too low.  On the other hand, if you choose 3" lightweight feathers and a jumbo 175 grain tip, you'll likely have too much FOC.  So try to avoid opposite extremes at the ends of the arrow, and choose an arrow setup that will give you an FOC balance of roughly 7-15%."

[Snapshot]

So long as the arrow flies right I don't know that there is such a thing as too much FOC.

[bucklucky]

Jeramiah, Im shooting Full Metal jackets 400's , 3 blazers veins, cut to 28 inches with 85 grain montecs and they flie just fine . We checked my foc and it came in fine. Dont over think your set up, just shoot the broadheads and see how it shoots. If it shoots good why worry about nothing.