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Discussion Starter #1
I have a question on FOC.First of all let me explain my setup,

Hoyt Alphamax 35
62# DW
Gold Tip 55/75 cut to 28"
100 grain points

I can not get good arrow flight with a high FOC.If my FOC gets above 10% my groups get bad but if I mess with the fletching distance from the nock up the shaft and I get the FOC between 8%- 10% my groups shrink big time.Can someone explain why when I get the FOC above 10% they start to shoot all over the place.Is the spine getting weak or stiff with a high FOC?
 

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I have a question on FOC.First of all let me explain my setup,

Hoyt Alphamax 35
62# DW
Gold Tip 55/75 cut to 28"
100 grain points

I can not get good arrow flight with a high FOC.If my FOC gets above 10% my groups get bad but if I mess with the fletching distance from the nock up the shaft and I get the FOC between 8%- 10% my groups shrink big time.Can someone explain why when I get the FOC above 10% they start to shoot all over the place.Is the spine getting weak or stiff with a high FOC?
You are changing your spine when you add weight up front and have to adjust accordingly. More weight up front means you will weaken the spine of your current setup.
 

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If you are adding weight to the front you tend to weaken the spine. If you are on the low end of the chart on spine, this might put you into a weak spine. For target the less foc is fine, but for hunting use the 12-15% margin, that might mean going to the next size up on shaft spine.
 

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10-15% IF you're shooting a fixed blade broadhead but if you're shooting a mechanical you can get by with less since they basically fly just like a field point.
 

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Discussion Starter #6
I will be shooting mechanicals,If I get the FOC between 8% and 8.5% that is where I get the best arrow flight.Most people worry about getting a high FOC in the 10%-15% but I have built alot of target arrows with a 6%-7% FOC and they fly great.
 

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How are you going about changing your FOC? When you move the placement of the fletchs you change the stablility of the arrow more than you change the FOC.
 

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Discussion Starter #8
I change the FOC by useing different fletchings from vanes to feathers from
1 7/8" to 5" and use different point weights from 75gr.-125gr.Also I know that the fletching distance from the nock does not change the FOC that much but you can change it a 1/2 of a % by moveing the fletch up and down the shaft and also mess with the arrow spine that way to.
 

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I would say that when your groups get bad you are weak spined. You could verify that by dropping the draw weight until the groups tighten up.

I really haven't calculated my FOC in about 15 years, I'm not all that concered about it and only shoot fixed blades. I haven't had a problem with pass thrus ever on deer.
 

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I have been experimenting with high to extreme FOC arrows for the last 3 months pretty intently. I have found that even if I purposely overloaded the front of an arrow, they would still group fairly well, just not in the middle. I have found that the higher you get your FOC, it will magnify any issues with your set up immediately. I ended up paper tuning my D350 from 5 yards to 30 yards every 6-8 feet and since I did that, I can shoot any arrow and they will all group. Currently I am trying to decide between some GT Ultralight Pro 300's with 175 grains up front, 18.1% FOC, 455 grains total weight and some CX Maxima 450's with 150 grains up front, 16.8% FOC, 465 grains total weight. Thinking I might end up with the Maximas, but they are freakin expensive here. Good luck. You may want to check out the 'Extreme FOC' thread on here too for some pointers and suggestions.
 

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Right now according to a web site calculator I"m at 10.3% FOC with an 85gr tip. Personally, I think that's plenty good since I plan on using either a mechanical or small fixed blade that will fly like a field point. If I were going to use a larger fixed blade with a lot of surface area that would plane badly then I'd probably want more FOC, say 15% but for my needs 10+% is plenty.
 

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High FOC will never cause bad flight. Think about it. How the Hell could it? High FOC only makes sure the arrow stays pointing forward. :doh:

If your groups open up when increasing the FOC then it's spine or the different fletching is making contact. It's just that simple. It's nothing else.

For example....did you cut the arrows shorter when adding weight to the front and taking it off the back? If not you could have drastically changed the arrow's dynamic spine and that WILL make them fly differently.

In reality, all you did was find what dynamic spine works best. :D
 

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Are you talking for hunting or 3D? I have 3% FOC on my ASA setup and my arrows group fantastic at 50 yards! Tune your bow to your arrows trying shooting a group with a turn added to both limbs then try a group by taking off a turn on your limbs from your starting weight you may be surprised! You may need to break the spin down or stiffin the spin up a little.
 

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Your setup specs don't seem to indicate a weak spine just from glancing at them, but I would definitely experiement with a higher rated spine. Your experience tends to show that increasing the stiffness gives better results. What is your end purpose? Target or hunting? This can make a big difference in your future choices.

Raising the FOC itself should not hurt accuracy in any way that I have ever seen. That's why I would surmise that it's a stiffness issue that is a side effect of increase point weight.
 
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