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Discussion Starter #1
Just bought some new ACC shafts put trueflight 2" feathers on back with g nock. Put PDP inserts in with 40 grain weights and a 125 grain top hat point. This gives me 17.9% foc. Shooting it out of a 2015 Hoyt Nitrum 34 28.5" dl at 65lbs. Did I overdue it or will this work out. I'm thinking it will fly pretty good and hit hard just looking for some opinion. Thanks
 

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Hunter of many things
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What arrow spine did you buy?

How long are your arrows?
 

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The Ranch Fairy
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If you have a 400 or 340, darts and pass throughs baby!
 

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Ive got some arrows set up with 425 grains up front so from a foc standpoint id say your more than just fine. Big question is what spine acc and how long are they cut to make sure the dynamic spine isnt too weak
 

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As long as you have the right spine 25-30% foc will not hurt you at all. Just watch those ACCs. They don't have the best memory. Give them a small flex and they wobble like bent aluminum arrows. Just keep an eye on that.
 

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Discussion Starter #6
I'm shooting 3-60(340) spine got to shoot them today for the first time and they hit like a freight train compared to my gt's
 

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which pdp inserts did you use to fit the shaft? i’ve been using black eagle 42gr in my accs but they are just a tad bigger than the outside of shaft and makes it a pain to pull them out of bag targets, also leaves a bigger hole than needed in the target when removing the arrow..

also 18% foc will be fine..

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The Impartial Archer
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You really can't have too much FOC....especially if you are only at 17.9%. The bigger issue is how that FOC effects the spine for your spec's.
 

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You can definitely have to much FOC depending on what your trying to achieve.

Your setup is well within a good balance and will work just fine


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I’m running 25% at this time.

Adding tip weight to increase foc only has one con. Total arrow weight. If your happy with the total arrow weight then there is absolutly no way to have to much foc.

When building foc arrows you need to make sure correct spine so you have the correct dynamic reaction when setting up and tuning.
 

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(aka lug nut)
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Scholarly article titled "Aerodynamic Properties of an Archery Arrow". Looking at the transition between laminar and turbulent airflow for an Easton ACE, with a bullet point versus a "streamlined" cone type point. Wind Tunnel testing, high speed cameras, Magnetic Suspension and Balance System and a compressed air canon, shooting arrows at 70 meters for empirical testing.



ACE arrow with the bullet point and the cone shaped point.



Wind Tunnel and the Easton ACE supported in mid-air with Magnetic Supports. How COOL is that?



Air Cannon for launching arrows during the 70 meter testing.

So, what's the bottom line? The boundary layer going from turbulent to laminar is not your friend. Better to keep the boundary layer turbulent, on purpose.
A 15 cm difference in point of impact 70 meters away (76 yards), based on aerodynamic drag effects, during empirical testing. SWEAT the details. It makes a difference.
 

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Scholarly article titled "Aerodynamic Properties of an Archery Arrow". Looking at the transition between laminar and turbulent airflow for an Easton ACE, with a bullet point versus a "streamlined" cone type point. Wind Tunnel testing, high speed cameras, Magnetic Suspension and Balance System and a compressed air canon, shooting arrows at 70 meters for empirical testing.



ACE arrow with the bullet point and the cone shaped point.



Wind Tunnel and the Easton ACE supported in mid-air with Magnetic Supports. How COOL is that?



Air Cannon for launching arrows during the 70 meter testing.

So, what's the bottom line? The boundary layer going from turbulent to laminar is not your friend. Better to keep the boundary layer turbulent, on purpose.
A 15 cm difference in point of impact 70 meters away (76 yards), based on aerodynamic drag effects, during empirical testing. SWEAT the details. It makes a difference.

We know increasing foc cause more drag. So we have to do something to help this. This is why you decrease helical to offset. You decrease the amount of offset and you decrease this size of the vanes. These are things that need to be done when increasing foc.

Now we also need to look at this. Are we talking about target shooting or hunting. Because very few people hunt at 70meters.
 

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(aka lug nut)
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We know increasing foc cause more drag. So we have to do something to help this. This is why you decrease helical to offset. You decrease the amount of offset and you decrease this size of the vanes. These are things that need to be done when increasing foc.

Now we also need to look at this. Are we talking about target shooting or hunting. Because very few people hunt at 70meters.
Easton ACE arrows are premium target arrows, so the purpose of the study was the aerodynamic effects for point shape, shooting at 76 yards.
 

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Easton ACE arrows are premium target arrows, so the purpose of the study was the aerodynamic effects for point shape, shooting at 76 yards.
I’ve seen some studies that show the turbulence on field points. Pretty interesting.

But I will still say no such thing as to much foc. I’ve hunted with up to 25%. I’ve shot up to 39%. With zero problems but I was limited to distance. But the distance wasn’t due to foc is was due to total arrow mass

Where most people have problems with efoc or uefoc arrows is not un$erstanding how to tune them. Arrows with this type of foc needs to be dynamic tuned. Not just the standard tuning that we have all been taught. That type of tuning is great with standard set ups.
 

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(aka lug nut)
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I’ve seen some studies that show the turbulence on field points. Pretty interesting.

But I will still say no such thing as to much foc. I’ve hunted with up to 25%. I’ve shot up to 39%. With zero problems but I was limited to distance. But the distance wasn’t due to foc is was due to total arrow mass

Where most people have problems with efoc or uefoc arrows is not un$erstanding how to tune them. Arrows with this type of foc needs to be dynamic tuned. Not just the standard tuning that we have all been taught. That type of tuning is great with standard set ups.
Super high FOC can be lotsa fun at just 20 yards. RESULTS based tuning. Gotta shoot actual arrows (that means with vanes) at your intended shooting distance and actually look at your groups. Yup, "dynamic" tuning. The study basically concluded that sanding your points (bullet style points) will keep your arrows flying in the turbulent zone for aerodynamics, and this can be a good thing, for accuracy, at really LONG ranges...like 76 yards, for skinny target arrows. Spin Wing vanes were used during the test. If you are shooting 30 yards, with fixed blade broadheads...no need to do anything, the fixed blade broadhead guarantees you have turbulent airflow.
 

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The Ranch Fairy
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I am no physicist, but have enough science background to confuse my self! Here's how the Ranch Fairy brain works.
1. We are not shooting in a vacuum, the atmosphere is 14.7 PSI pushing down (FACT), in the case of bullets and arrows, the projectile (for a visual) is moving laterally through very, very, light ballistic gel that may include a little wind or extra humidity. Literally it is pushing, like a needle into a nerf football (again visual only) from release to impact on target, animal or Earth.
2. The projectile is working hard to stay in flight (shaft drag) 100% of the time.
3. Gravity seems to be a fact and is annoying for pin gaps
4. The arrow is not perfectly aerodynamic (holy smokes do we put wings on the front when hunting?)
5. The arrow is ever reducing in speed from the second it leaves the string.

I know people get sick of hearing me blubber on. I cannot prove this, trust me I'd like to find a scientific way to do it (anyone out there, chime in if you got it). But SOMETHING happens at 16% FOC. I don't care about arrow mass here, just FOC. I bare shaft tune 340's / 300's and 250's on my Xcursion 6 and any other bow(s), including my friends and kids, etc. I THINK, the point starts pulling the shaft and the shaft, the whole shaft, starts dragging like a kite tail. A huge kite tail, this is a good thing. When I get down around 12% FOC, I THINK the arrow is pushing and trying to steer from the back. It is much harder to bare shaft a low FOC Arrow, my form has to be perfect. Dude, the A.D.D doesn't allow for that.

This outcome based observation, and yes, yes, I am a fanboy of FOC. There is no spine chart or computer program for this. I have added 100 grains (nothing crazy) to a bunch of different setups, usually 28-30" 340's and the arrows just seem to behave, especially when you put broadheads on the front. I THINK, the weight up front overcomes the aerodynamic impact of having a broadhead (wings) up front. Lower FOC, the arrow pushes the broadhead, and if your form isn't good, or maybe you are excited because bowhunting is exciting and its 38 degrees at 8:30 am, you didn't shoot 43 warm up shots to "engrain your shot cycle" because you were late leaving camp, well................arrows that behave when things ain't perfect, are way better.
In my world, I only care about one thing. Accurate delivery of a broadhead to the thorax of the intended critter a la carte'

So for those un official protectors of the AT forum, flame me on email, [email protected] and hate. No reason for it here, we are trying to help out. I mean its "Archers helping archers" man!
 

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Troy. I agree.

It’s fun to talk about all this air disturbance at the tip and the resistance as the arrow flys through the air and the amount of drag we get. It’s fun to see test being done in wind tunnels and to see how the tip changes the air flowing around it. But in the end. Most archers don’t give a crap. There are only a few here that even talk about it. It’s easy to see who. Just look at the foc post haha.

In the end what we all need is to make sure the arrow has enough mass. Enough foc. The right broadhead and great flight so that we may go kill something. You need an arrow that if you hit major bone you still bust it and get into that animal and that takes mass to break and foc to keep the arrow moving forward after bone breach.

What is amazing to me is the lack of knowledge, and I’m FAR from being where I want to be. But if people would just step back look at a little physics. Understand what is going on then this type of post would not be happening.
 

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1. We are not shooting in a vacuum, the atmosphere is 14.7 PSI pushing down (FACT),
Air is fluid, like water, so it does not push "down". If an object is neutral buoyant and you place at mid depth in a volume of water, it will not sink to the bottom if you add more water above it. The added weight of the extra water above the object increases pressure on all sides of the object, not just on the "top" of the object.
 

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Air is fluid, like water, so it does not push "down". If an object is neutral buoyant and you place at mid depth in a volume of water, it will not sink to the bottom if you add more water above it. The added weight of the extra water above the object increases pressure on all sides of the object, not just on the "top" of the object.
Air is fluid. I believe Troy made a comment on that.

He also talked about gravity.
 
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