Do you worry about Front of Center?

[tomasw1]

I'm trying to come up with an arrow recipe for my M380 next season. So far I have it most of it down. Blazers, Luminoks, 18" BE Zombies and still working on a BH. Right now I'm running very closely to the above with BEE, 125gr BHs and 92gr insert and I'm getting a 13% FOC. That seems a little low to me considering I was thinking of going fixed blade. Gold Tip has their FACT insert weight system, and I am thinking that may be the way to go as I believe the ID is the same between the Gold Tip Laser and the Black Eagle Bolts. The fact that you can add and remove insert weight even though the arrow is already built seems like a great option. Your thoughts are greatly appreciated.

[galamb]

Some think FOC is VooDoo.

After doing significant personal, non-scientific testing (like 2000 shots with numerous different arrow/insert/broadhead combos), I have found that extreme FOC works way better for "my set-up".

The absolute tightest groups I could get were achieved with FOC's greater than 20.

I have personally settled on 22.5% as a sweet spot.

At 15 or less my target looked like I had hit it with a shotgun.

Your experience may vary..

[Kegbelly]

The luminok adds roughly 19 grains of weight to the rear of the arrow compared to a flat plastic nock, so that does change the FOC balance point a little. But 13% with the components you have listed sounds awfully low, plugging your components in the Gold Tip calculator you should be around 20% with what you have listed.

[newbie]

i agree that FOC sounds low for the components you listed.

[Boo]

I don't measure or calculate anything (I'll leave that for the OCD crowd to feed that empty hole ). I pretty much just assemble an arrow and shoot it. It's the proof in the pudding I'm looking for, not the numbers.

[tomasw1]

Hmmm. You're right, the Goldtip page lists me way higher. Maybe my math was off. I calculated it by by measuring from the balance point vs arrow length and using a formula I found online. (The Goldtip page was down when I looked originally). I will have to play with that. Thank you for your insight!

[MI Yeti]

With a brass insert(110grain) and a 100-125 grain broad head FOC is plenty , at least for my bows . In my modified vixen I shoot stock 20" laser2s with 100 grain points and it is a bit under 21% foc . in my exocet 165# I shoot stock 20" laser2s with 125 grain points and is a bit over 22% foc . the accuracy is good in the bows I shoot them in so i don’t worry much about the math , good thing as i am terrible at it

[nchunterkw]

Hmmm. You're right, the Goldtip page lists me way higher. Maybe my math was off. I calculated it by by measuring from the balance point vs arrow length and using a formula I found online. (The Goldtip page was down when I looked originally). I will have to play with that. Thank you for your insight!

There are different methods used to calculate FOC. To compare numbers whoever you are comparing with needs to measure it the same way you do. The numbers generally don't vary greatly but with a longer BH they might.
Here is my method:

TotalL = measure from the back of the nock to the end of the insert
Mid Pt = mark the arrow at half of TotalL
Bal Pt = mark the arrow where it balances on a thin edge.
Delta = measure the distance from Mid Pt. to Bal Pt.

FOC(%) = (Delta/TotalL)*100

example:
Total L = 20", Mid Pt = 10", Bal Pt. is 3" toward the front from Mid Pt (this is Delta).
FOC = (3/20)*100 = 15%

Hope this helps.

Boo - You keep getting it wrong!!! It's C D O because then the letters are alphabetical!!

[amythntr]

....great post....my Blackout setup is:

Lumenok 28g,
Blazers 18g,
ZS 18" @ 9.1g/"=163.8g
Brass lock n load=92g
Spitfire 100g
Arrow wrap=10g

Total "arra" weight 411.8g

FOC per GT University "summa spam laude" calculator= 16.68% gove or take a 100th or 2...

Anthony

[amythntr]

....great post....my Blackout setup is:

Lumenok 28g,
Blazers 18g,
ZS 18" @ 9.1g/"=163.8g
Brass lock n load=92g
Spitfire 100g
Arrow wrap=10g

Total "arra" weight 411.8g

FOC per GT University "summa spam laude" calculator= 16.68% gove or take a 100th or 2...

Anthony


the spam machine will not print that bad word in between summa and laude....

[Jerod B.]

My bolts will have about 26% FOC. Not 30, but it'll do.

[Kegbelly]

Hmmm. You're right, the Goldtip page lists me way higher. Maybe my math was off. I calculated it by by measuring from the balance point vs arrow length and using a formula I found online. (The Goldtip page was down when I looked originally). I will have to play with that. Thank you for your insight!

I noticed it because your component list is very similar to mine except I use a lighter insert and so there's no way a heavier insert could give a lower FOC.
And to dispel any rumors of me being OCD I was building for total arrow weight, not FOC, and mine come in a little over 18.1824% at 399.92413 grains with a 65.12784 grain insert, and the FOC just was what it was
Yes it does matter how it's calculated, broadhead length and what points you measure from.

[Lake shooter]

I shoot Diablos with Lumenocks and 125 grain Swhackers. Don't know the FOC of the set up and don't care, because the damn thing is a tack driver out of my 380!

I bought a crossbow for two reasons: my right shoulder was going downhill and I was sick and damn tired of tinkering and tuning with my old Mathews and my arrows!!!!! I do not now and never will target shoot because I bought this rig for hunting, period. As long as I can put arrows down range and hit where I'm aiming, that's good enough for me.

On the FOC thingy: I have always thought that it was crazy to NOT measure to the tip of the head, only the insert, but THEN have the head installed to measure FOC!!!! Somewhere along the line too many engineers and scientist types had to get in this mix! Think about it logically: even if you are shooting something like 125 grain target points and 125 grain broadheads, not measuring to the tip of the head will give you a different FOC IF the broadhead is longer than the target point, simply because it's center of mass is further forward than the target point.

On the other hand, if you were to include the point and BH in the total length AND the two heads were actually the exact same weight, the FOC will be very darn close to the same also.

[bob watkins]

i with boo make them and shoot them i never had a problem makeing things fly just adjust as you go. never worried about foc. 18in zombies or bee 110 insert 100gr slick trick or ramcat nufletch nocks blazers

[SEW]

On the FOC thingy: I have always thought that it was crazy to NOT measure to the tip of the head, only the insert, but THEN have the head installed to measure FOC!!!! Somewhere along the line too many engineers and scientist types had to get in this mix! Think about it logically: even if you are shooting something like 125 grain target points and 125 grain broadheads, not measuring to the tip of the head will give you a different FOC IF the broadhead is longer than the target point, simply because it's center of mass is further forward than the target point.

On the other hand, if you were to include the point and BH in the total length AND the two heads were actually the exact same weight, the FOC will be very darn close to the same also.

For decades, I've thought this. It's just common sense to me. Maybe because we're both from Arkansas and think logically. I try to approach everything possible as scientifically as reasonable.
Now back to a few accepted principles: the less steering potential of the point (field point --> expandible ---> fixed broad head) , the less FOC required, the more the drag of the vanes, the more FOC required (helical vs offset vs straight), lighted nocks have more wt thus requiring heavier points, the more the FOC the tighter the grouping (if enough spine ) until a certain FOC is reached and after that all that is gained is poorer trajectory (and maybe a little more penetration).