# FOC, Trajectory and the Magic number?



## RaptorX (Dec 28, 2007)

With all the reading and advice on the subject of FOC, many feel to go with as much FOC as one can tune as if no limit, and yet, some very credible responses are, there are benefits to not going "to much". Shaft weight can be a big factor against raising FOC, but possibly not against some other important aspects of flight. 
Yet a recent acquaintance of mine, great archer, suggested during a conversation about a "magic number" regarding FOC, being around 13.5%. This archer is very knowledgeable, jaw dropping in ability (still can't find it, it's out there somewhere) and his job and reputation suggests he knows exactly what he's talking about.
I'll stop here because I don't want him involved when the arrows fly :fear:.
I still think for me, the magic number is a little higher, but not so high maybe.

My experience starts with a Draw Weight with Arrows on that bubble of just reaching 90 meters, to arrows reaching with a little left to spare, or a lot left to spare, all at the same Draw Weight...

Example: (the decimals regarding the FOC percentages were so close in each case I rounded).
All shots were with a draw weight of 38# through the clicker, using the same device to measure.
All shafts fletched with Pink 45mm Kurly Vanes, straight, no offset.
The X-Pert Shafts were slightly shorter .5" for tune, but I don't feel this had much shaft weight affect for those arrows vs the ACEs.
**Sight bar in a few notches, and stays there through this experience (I like it there)**

--I shot some Cartel X-Pert 660 shafts (heavy A/C Korean shafts about 7.5+ grains per inch, actually like these a lot) with Kurly Vanes and 90 grain X-Pert Break Off points (full length, nothing broken off) 
FOC = 13% (this was not because of what I heard above, this was just the way they tuned, long before).
Shafts reached 90m, and flew well IMO, but not much to spare really even with the sight bar in a few as mentioned.

--Then, I shot ACE 620 shafts (6.1 grains per inch) with 100 grain Easton SS break off points, full length, nothing broken off, with kurly vanes again, fletched the same way, at 38# through the clicker (of course I re-tuned, and in fact different riser, but same limbs).
FOC = 18%
Shafts reached 90m easier, several clicks higher up on the sight bar from the cartels, but only several, I'll explain further.

--I changed the points on a few of those ACE arrows, breaking of a segment of the point so it was 90 grains, and they didn't show much tune difference, at all (not surprising to me, just a slight plunger adjustment was all that was needed, if it was needed, didn't have to even adjust DW in the slightest).
FOC = 16%
I haven't shot them at 90m yet (I have at 70m and 80m (ran out of room at this location)), but I think I know what would happen as they were higher at 70m than the other ACEs with 100g points (based on the findings later they looked like they would stay there especially reviewing at 80m). This day there was a breeze, a steady one but not more than 8-10 knots. I did NOT notice any wind drift difference at all between the 90 and the 100 grain point ACEs.
I'd shoot an end of 100g points, and move sight for height of 90g points (with segment broken off), and I could group the 90g ones right in with the 100g ones. 

Without going into too much about setup and did I do this or that right, the question I have is in the flight of the arrows at that DW, and how they fly on a low or no wind day, and how and if with those FOC numbers, the trajectory towards the target out weighs the advantage of a higher FOC (when I say higher, I mean not going below recommended, but topping out at near heaviest recommended by Easton), with such light shafts like ACEs, even on a real windy day? (I think for that ACE shaft, Easton Recommends 90-100g points.)

The X-Pert (90g point), 13% FOC, flew with a good looking trajectory, and grouped well for me when I performed, and yet, my aperture was about as low as it would go, to get to 90m at that DW. Both ACE arrows (with different point weights) out flew the X-Perts of course, being lighter, and a small amount thinner, it was expected.

Here however is what surprised me...The Sight Marks on the sight bar for each.
The trajectory of the heavy shaft light point was similar to the light shaft light point (but overall lower from 15m on, because, even at 18m there was a slight, but noticeable difference, but not between the ACEs at all. At 30 and 50 meters, a big difference.).
But then the point  of what would happen after the target (where would it fall if I missed it). This, and with the ACE 90g point, seeing no drift in 8-10 knots. But what happens when the wind is bad for the heavy point ACE, and if the wind is in my face hard, based on the following graphics, would I even reach? Curious because based on the graphic showing the kind of differences in sight bar and trajectory, the Highest FOC, on the lightest arrow, will actually not go much farther than the heaviest arrow with the lightest point once past the target, and the lightest arrow with the lightest point (of still an FOC of 16%) will go far beyond both, and shows no sign of any more drift in a 10K side breeze than the 18% FOC arrow (but would it show a significant difference in a 20-30 knot side wind?).

My subjective conclusion seems to be (please, shoot holes in it, I'm expecting to get beat up pretty bad by this and I'm getting used to that here, at least I hope it's with patience and careful educative advise):
For anyone with a low DW (up to about 40lbs) recurve, I believe, that the ideal FOC could be maintained between 13%-16%, for someone shooting over 40lbs and up to 50 with a recurve, the ideal FOC could be between 16%-19% (and all carbon arrows less, as suggested by easton?). Does this make sense?
But at 38lbs DW? It appears, the sharp drop getting sharper from 70m to 90m, appears this would leave the arrow more susceptible to elements at the end of flight for that distance, and lend itself to more inaccuracy or inconsistency do to the ending trajectory, or no?

I'm not making any claims at all, I'm asking all of you for opinions on these findings with my experience (ever the tinkerer), based on your expert or not, experiences or possibly, scientific knowledge. 
Am I right to assume that the higher FOC arrow in this case is less accurate or more effected by the elements with a lower Draw Weight Bow?
Am I right to assume that a flatter trajectory is better in a case like this, where I can shoot a 90g point 16% FOC arrow rather than a 100g 18% FOC arrow which drops faster only after a certain distance, with a draw weight low enough that this should matter?
Several posts I've seen about those trying to reach 90m with low draw weights etc. and if they are trying to keep their FOC up to 18% or more, it seems to me they are making it hard on themselves for nothing, or, am I wrong here too?
Anyone else heard of this 13% FOC magic number?
Lastly, for those that reply (or at least care to), may I ask what FOC your arrows are at right now (if you know)? I'm staying at 18% for now but honestly thinking of changing all my points to get 16% and a flatter trajectory and distance as I am thinking I lose nothing, but hope to learn something here.

Thanks, if you've read this mess...:blah:
-ps, one of my personal best practice scores (this one at 70m), was with those X-Perts, heavy shaft and but barely 13% FOC, one a cold, windy day with heavy drizzle. 
Still can't figure that one out:dizzy:.


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## rgauvin (Feb 20, 2007)

there was a thread last year that outlined the advantages of some arrows versus others and their flight trajectories. the one post in it was pretty in depth and I think it would add value to this one, I am just having trouble finding it.


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## chrstphr (Nov 23, 2005)

i use to shoot 12.75% FOC with 350gr total weight (110gr point) 450 X10 with 51 LBs at clicker, 208 FPS

I now shoot 17% FOC with 320gr total weight (110gr point) 550 X10 with 46lbs at clicker, 208 FPS

the higher FOC lighter arrow groups better for me at 70 and 90, though the arrow itself is shorter than the 450 was that i shot. Dont know if my info helps you. i do have more drop between 70 and 90 now but i can still reach 90 with room to spare on my sight extended all the way out. 


Chris


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## lorteti (Apr 14, 2008)

I get 16.5 FOC on 28" McKII with 44lbs bow. I think around 16 FOC is the ideal number.
But how are you be able to get 18 FOC with 100 point on ACE? What is your arrow length? How did done the calculations? I use the Beiter website FOC calculator.

jx


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## RaptorX (Dec 28, 2007)

chrstphr said:


> i use to shoot 12.75% FOC with 350gr total weight (110gr point) 450 X10 with 51 LBs at clicker, 208 FPS
> 
> I now shoot 17% FOC with 320gr total weight (110gr point) 550 X10 with 46lbs at clicker, 208 FPS
> 
> ...


Thanks Chis,
I kinda expected this too with your DW, that a higher FOC would be better at 44#, it seems the drop off is less an issue for you at 90, it almost seems to me that there is a relationship to optimum FOC and the actual DW that is used (this may be no news to anyone).
From what am thinking, you probably found your optimum at your DW, is my thought.

Last evening, I tallied up a round at 50m, I knew I did well, but it was tallied after I posted this thread.
I setup my backup bow Monday and finished primary tuning last evening after work (new riser this weekend) intended for more indoor around 37#, same riser as my outdoor, but tuned to my X-Pert 13% FOC, 90g point shafts as I still have many. I got these to group very well at that DW as I tuned it in rather quickly (nailed the grouping even though bare shaft showed slightly low and stiff). But I went outside to shoot at 50m for a game I'm involved in with a friend, while the bow felt good and quiet and I still had daylight.

Turns out, I shot a personal best at 50 (my most difficult distance) last night (37#, 13% FOC, from 50m , with the X-Perts (7.5+grains per inch) which are 29" nock to cut, 3/4" tip on 90g full length BO X-Pert points).

292 
(this is good for me, and it was getting dark). Is that 13% FOC a magic number? Probably not, but is one's FOC able to be optimized and should be more related to DW that most discuss?

And yet, don't know if I'd reach 90m with that setup without moving the sight bar in quite a bit.

My other bow, I like 38-40#, and it's currently 38# through the clicker and shooting ACEs w/100grain points because I can tune them (so tuning the arrow to the bow, my DW between the two shaft setups right now is not much more than a pound, though height/distance is far different until about 90 or beyond). 

I'm just curious and thinking that 16% FOC might be better for that setup and improve the groups at longer distances. I would't be losing anything just gaining more distance and accuracy is my thought, but don't want to get caught regretting 16% in a side wind, or regretting the 18% in a head wind, (what's the least of these evils?). 
I just don't really know, as the 18% is doing fine.

My good friend (mentor), and one who has helped me over the last few months (ridding me of bad habits and bad thinking...will probably talk to me about this..:wink, shoots about the same DW right now because of a shoulder injury (not archery related), but he's shooting 570 ACEs (longer DL) with 100 grain points and FOC I believe is around 15+%, his arrow flight is excellent, but, I have to attribute that to him, he's way beyond me skill wise. Yet, that also has me thinking that my ACE 620s would fly better at 16% than at 18% (trajectory wise).
Just, can't stop wondering if at longer distances I would get better grouping out of 16% FOC due to less drop off, with little loss of control in wind.
Is the Higher FOC just hurting me?



Thanks again


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## RaptorX (Dec 28, 2007)

lorteti said:


> I get 16.5 FOC on 28" McKII with 44lbs bow. I think around 16 FOC is the ideal number.
> But how are you be able to get 18 FOC with 100 point on ACE? What is your arrow length? How did done the calculations? I use the Beiter website FOC calculator.
> 
> jx


Thanks, loreti, I'll try that calculator when I get the chance.
I do the calculations the old way once the arrow is setup.

ACE 620 shafts (cut shaft only is just shy of 29.25) use Beiter InOut #2 Nocks, 100-90-80 grain Easton ACE break off points at full (100g) length. 
Use 45mm Kurly Vanes for fletchings. 
I rounded the FOC, from about 17.9%. But truly, I'm just curious where the optimum is in relation to DW and Arrow Weight, all things considered.


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## stevegabriel (Apr 18, 2007)

can you privide a link for that calculator?

Thanks.


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## lorteti (Apr 14, 2008)

here is the Beiter FOC calculator link: http://www.wernerbeiter.com/en/products/tools/BalanceClip.php

jx


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## chrstphr (Nov 23, 2005)

lorteti said:


> here is the Beiter FOC calculator link: http://www.wernerbeiter.com/en/products/tools/BalanceClip.php
> 
> jx


Using the Beiter calculator, i am at 15% FOC currently. 


Chris


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## RaptorX (Dec 28, 2007)

chrstphr said:


> Using the Beiter calculator, i am at 15% FOC currently.
> Chris


Very odd indeed. 
We have a controversy...
The Beiter calculation is different, they measure the balance point from the front, and Easton measures it from the nock groove.
Beiter uses an arrow length that says "to the point", the beginning or tip of the point? we assume the tip.
Eason, uses an arrow length NOT including the point, from Nock Groove to Cut end of shaft. 

The results, differ greatly, and it seems, the longer the arrow, and the heavier the point the greater the difference (initially).

I used the Easton Calculation at the end of their famous tuning guide, but, it is older, and Beiter is very accurate about and reputable also. 
Who do we believe.

Easton's Calculations say my X-Pert arrow is at 12.9, Beiter says it's (if to end of point, 10.1%, if to cut end of shaft and beginning of point 12.3%)

Easton's Calculations say my ACE arrow is at 17.9% as I recall, and Beiter says it's (if to end of point 14.7%, if to cut end of shaft and beginning of point 16.1%)

Now what??????
Graphics below are of the two different calculations to find FOC:


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## Hutnicks (Feb 9, 2006)

I would tend to side with Beiter on this one. You must consider the point as an fully integral part of the arrow and that would mean its inclusion in the overall length.


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## jamaro (Apr 13, 2003)

hmmm.... this is not good... which one is it?
I have always used the easton way...


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## Jymbeau (Jan 19, 2006)

Isn't it possible that beiter's "to the point" means up to but not including. This would be just the shaft just as Easton's charts measure.
Maybe...


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## RaptorX (Dec 28, 2007)

Hutnicks said:


> I would tend to side with Beiter on this one. You must consider the point as an fully integral part of the arrow and that would mean its inclusion in the overall length.


Well, I was feeling this too. I just decided to validate and calculate my arrows again, but not one, almost all of them.
I think part of the error, is human (sigh), but not all.
I don't have the 90 grain points in those two arrows anymore (this is a clue), and they are not marked yet, so I don't know which ones they are anymore.
My average, the easton way, being as accurate with the balance point as possible (figuring this is the only mathematical part of the formulas open to human error), indeed, I got ranges. And, I must admit the average and most of the ACEs were closer to 16.8% FOC, leading me to believe the 90g point ones were closer to 15%. Why the diff? Re-playing the process of arrow building in my head, is the inability to be accurate with the hot melt glue one uses (especially, if one replaces a point, and inserting the second heats and pushes the residual glue in the shaft back down the shaft), and if replacing a point, and gooping it, that explains the few that came up to about 17.7 - 17.9% possibly.
I also found variances in the X-Perts. I found that being an 1/8 inch the off the actual balance point of any, in some cases, if balancing, and using your finger tip to find the point instead of marking, then tape measuring, this is so possible, the percent difference could be a whole % between two arrows, that really aren't.

Yet, all being said, as accurate as I could be, the numbers from the Easton Method, and the Numbers from the Beiter method if you use the arrow length to the CUT end of shaft (or BEGINNING of the point with the Beiter calculator) are about the same (so why the bigger difference using arrow length to end of point??).

Glue, hmmm.

My apologies for considering the FOC calculated from one arrow. I apparently was off more on the ACEs as I was the X-perts, however.
Still, we're talking about 12.8% average X-Perts, and 17% average ACEs vs I'm guessing, about 15% (90g point) FOC ACEs.

Lesson learned.

The question still is one that is valid, the drop of experienced with a DW that "just makes it" with a high end FOC (recommended range from easton or high as you can tune), to a better trajectory "easier reach" lower FOC but still within recommended range. arrow. Less drop off by the time it reaches 90m using the same DW, and the lesser of the two wind evils (side and head on). Side may cause more drift with less FOC, but at that critical reach factor, Head on may cause the arrow to "not make it", and drop off so quickly after 70 that accuracy is in question, or a nasty head wind can take you out.

Is Beiter referring to the END of point (doesn't say, or to where the point meets shaft (we seem to agree, they mean the end of point, but that makes the FOC definitely differ from Easton by a pecentage or two in some cases)).
My opinion is, Beiter, has considered the difference in the "length" of today's points, ranging from 1/2" to 1" (and we all know there is more weight in the shaft with some points than others), and yet, we start by calculating the balance point, which to me I assumed took care of this (but instinct tells me there is more that is unclear about the calculation, and that both are estimates). 

I think I'm beating this to the ground, but feel the same as Coach Jim C about Beiter's (they don't estimate much, the seem to know). And if right, this could be why so many go over easton's calculation, and find good results. "Hence, the highest you can tune to".

However, what about the DW to FOC relationship? The 100g reach just fine, but the 90g definitely flys with a better trajectory and possibly accuracy it seems, with little (8-10 Knots) or no wind). And for those who's DW and arrows barely or don't quite make it, trying to keep the FOC on the high end?
Today would have been a good wind test, yet, I couldn't shoot, dang.

Thanks to all that responded. Somewhere in these two options I'll find the best by half 90g and half 100g points, and marks for both. Then, just shoot my brains out and see which set over time produces the best results.

More input is always welcome (So, no one else has heard of this "magic number of 13.5 FOC...? Sure nailed a personal best for me.
Yet, most likely its my improvement with the coaching of a good friend and archer who can watch me at times, as I said before, ridding me of bad habits and bad thinking.
But the question interested me so much.:wink:


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## RaptorX (Dec 28, 2007)

Jymbeau said:


> Isn't it possible that beiter's "to the point" means up to but not including. This would be just the shaft just as Easton's charts measure.
> Maybe...


I kind of mentioned this above, and checked it (took some time).
If this is true as you suggest and I think it just might be, the numbers are definitely closer together in calculation, as I've just discovered (and discovered some human error (including my own) in calculating as well, that could be possible).

Thanks!


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## chrstphr (Nov 23, 2005)

Beiter way im at 15%

easton way im at 16.6%


either way i guess im close.


Chris


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## RaptorX (Dec 28, 2007)

chrstphr said:


> Beiter way im at 15%
> 
> easton way im at 16.6%
> 
> ...


From what I've seen from the best Archers I know, you are right in there!
But, that's just from my observation, no expert obviously. I guess I am too, at the high end and of what I can tune to. So, there I've decided to stay.

I'll Just "Shoot Away"!!!:tongue:


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