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Discussion Starter #1
I usually don't venture over to this side of the forum but I have a technical question. I have calculated the FOC for my arrows and I think it's telling me that I need to use 125 grain heads instead of the 100 grain heads that I have. Before I go out and buy new heads, would someone be kind enough to confirm that I'm doing this right and I indeed do need new heavier heads?

I shoot a 28" arrow including the length of the head. Its balance point for my finished arrows is 15.25" from the nock end. I have attached the FOC calculation which hunter5425 posted on another thread. This is what I followed except that I included the length of the head which is what someone posted was the better way to do it. It appears my arrows now have an FOC of 4.46% which supposedly makes them "unstable." Which doesn't sound very good. I shoot 2219's which weigh about 14 grains per inch, so if I add 25 grains to the head, I figure that would move my balance point forward one inch so my FOC would then be 8.04%,Yes? Also, while on the subject, is this really important, or is the whole FOC deal really more for guys that are taking 100 yard shots as opposed to a 30 yard bowhunter like me.
 

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I think FOC is important especially with broadheads. I like to keep my hunting arrows at 12% to 15%.:)
 

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Discussion Starter #3
I thought I was trying to get to 7 to 10% but I did some more searching and I found that like you, people are saying 12 to 15% for a hunting arrow. If I'm doing it correctly, a 150 grain head would only get me to 11.6%. That's a pretty heavy head. My arrows would end up around 600 grains. They would likely drop pretty fast out past 20 yards but I guess they would penetrate.
 

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Calculate it just as the diagram you posted, you only measure to the end of the shafy not including the insert, never include the point. The foc will change from broadheads to field points but only because of the weight being further away from center with broadheads; that causes the balance point to move further out so you will have a larger FOC with broadheads than field points. The only measurement that should change reguardless of the point weight or head style when checking foc is the balance point location.
 

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Unless you subscribe to any one of the several other methods of determining the FOC.
One of which does include the length of the entire arrow…(my personal favorite):D
 

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JAVI said:
Unless you subscribe to any one of the several other methods of determining the FOC.
One of which does include the length of the entire arrow…(my personal favorite):D
you should try hunting without points, inserts, and nocks sometime....very exciting to say the least.;)
 

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JAVI said:
Unless you subscribe to any one of the several other methods of determining the FOC.
One of which does include the length of the entire arrow…(my personal favorite):D
Mine Too!:)
 

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Discussion Starter #9
pblawler said:
Calculate it just as the diagram you posted, you only measure to the end of the shafy not including the insert, never include the point. The foc will change from broadheads to field points but only because of the weight being further away from center with broadheads; that causes the balance point to move further out so you will have a larger FOC with broadheads than field points. The only measurement that should change reguardless of the point weight or head style when checking foc is the balance point location.
OK, thanks. That cuts my arrow length down to 26.75" which helps add a few percentage points. I must be at 7.01% now. With a 125 grain head, it would be 10.75% and at 150 it would be 14.49%.
 

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Discussion Starter #10
JAVI said:
Unless you subscribe to any one of the several other methods of determining the FOC.
One of which does include the length of the entire arrow…(my personal favorite):D
JAVI, are you saying that my original result is what you believe to be the more accurate answer, i.e. 4.46%?
 

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HuntmDown said:
JAVI, are you saying that my original result is what you believe to be the more accurate answer, i.e. 4.46%?
I'll answer with 2 questions....

Are you shooting the arrow without the point?

And did the balance point not move, when you added the point?

Now either way could be considered correct, depending on your goal.
 
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pblawler said:
Calculate it just as the diagram you posted, you only measure to the end of the shafy not including the insert, never include the point. The foc will change from broadheads to field points but only because of the weight being further away from center with broadheads; that causes the balance point to move further out so you will have a larger FOC with broadheads than field points. The only measurement that should change reguardless of the point weight or head style when checking foc is the balance point location.
Like PB said, never include the Broadhead in the shaft measurement.
Just guessing, without having the exact measurements, but you are probably be around 8.5 FOC with the 100gr Head.
 

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How does your current setup perform?
 

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Discussion Starter #15
This is exactly why I stay on the bowhunting side of the forum.

JAVI, Of course I shoot my arrow with a point on it and the balance definutely moves with the point vs. without. Your link just gave me a score of 4.4.

Preacher and Pblawler's preferred method gives me a score of 7%.

Either method gives me a score below the 12 to 15% that people talk about so I guess I should probably have a heavier head. How heavy, who knows, but thanks for the help.
 

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HuntmDown said:
This is exactly why I stay on the bowhunting side of the forum.
Well with archery it's mostly theory anyway.. But sorry if my answer offended you... The point I was trying to make is... If the point is there and has an effect on the balance, Why would you not use it in the measurement...:angel:

As to the bowhunting side of the forum... it's just to ethical for me...:mg:
 

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HuntmDown said:
This is exactly why I stay on the bowhunting side of the forum.

JAVI, Of course I shoot my arrow with a point on it and the balance definutely moves with the point vs. without. Your link just gave me a score of 4.4.

Preacher and Pblawler's preferred method gives me a score of 7%.

Either method gives me a score below the 12 to 15% that people talk about so I guess I should probably have a heavier head. How heavy, who knows, but thanks for the help.
Do you think that NASA engineers calculate the balance point of the space shuttle with the load or without, do ballistic engineers consider the weight of the warheads for their FOC, and do FedEx cargo planes have a premarked center of gravity around which everything is loaded. Of course they do. Why wouldn't you.

The point/broadhead is still an aerodynamic surface and it contributes to the overall flight of the arrow and can change the aerodynamic and ballistic properties of flight. In my opinion it should be taken into consideration.:smile:
 

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The spine ofd the arrow is much more important and will be effected by the difference in tip weights. Careful what you wish for. I agree that you should have slightly more FOC but not at the cost of wrong spine.
 

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michihunter said:
The spine ofd the arrow is much more important and will be effected by the difference in tip weights. Careful what you wish for. I agree that you should have slightly more FOC but not at the cost of wrong spine.
Good point within reason... Spine and FOC can both be important to good arrow flight with a broad head...
 

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Discussion Starter #20
JAVI said:
Well with archery it's mostly theory anyway.. But sorry if my answer offended you... The point I was trying to make is... If the point is there and has an effect on the balance, Why would you not use it in the measurement...:angel:

As to the bowhunting side of the forum... it's just to ethical for me...:mg:
JAVI, Sorry, if a little frustration leaked out there. I do appreciate the help.

Michihunter - I believe I will buy 125 grain heads and then I'll shoot bare shafts a little to test the spine. If that seems to be a problem, I'll back a little weight off the bow.

Thanks for everyone's help.
 
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