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Discussion Starter · #1 · (Edited)
If it were possible to have three arrow of identical spine, length, point weight and total weight (accomplished by whatever artificial means to not alter spine) with the only difference being diameter say, a 9/32, a 5/16ths and a 11/32 would you not expect those each to shoot to a slightly differently POI off the same riser. Even if they flexed identically, the large diamter shafts are going to rest slightly further away from the riser sideplate. Center shot is a constant regardless, but for the sake of this argument let's assume it is cut to, but not past center. Would the larger diameter shafts not require slightly more flex to compensate for paradox (no don't drag it off in the bushes, we all know it's got to get around the riser whatever you want to call it). Bottom line, all else being equal you'd expect the 11/32 , 5/16, 9/32 to group left, middle, right respectively?
 

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The fatter arrow will act slightly stiffer.
 

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Wouldn't increasing the diameter make the arrow less center shot, and thereby making it weaker?

I did have some carbon arrow that were very close to aluminum 2216's. In order to get them to impact the exact spot I had to fiddle with the brace height.

Bowmania
 

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Wouldn't increasing the diameter make the arrow less center shot, and thereby making it weaker?

Bowmania
My take on it, is that incresing the diameter will make it less center shot and therefore, make it shoot to the left (from a right hand bow), as an arrow with a stiffer spine would.

I went on the 3 Rivers site and using their spine program, enetered data for a wooden arrow, where I could keep everything the same and just change the arrow diameter.

Dynamic spine incresed as I increased the diameter.
 

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Shoot the dang things and compensate for the differences these "numbers games" are boring! and that's not hypothetical! All that needs be done is to pull the string back with the arrow attached and go from there. sheesch
 

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Discussion Starter · #8 ·
I agree, but when you start cutting carbons "hypothetical" better get you close. I shoot a "plain jane" .500 spine carbon and with 125gr heads flight is all I could ask for. I always wanted a heavier shaft for hunting and I decided to get a shaft "test kit" and determine if I could shoot full length .400's and add point weight to allow me to shoot the 175 gr. Tigersharks that I like. Indication were that this was going to work. Until Big Jim got in some GT heavy hunter blems at a good price and I thought , why not. Didn't realize that they are fatter and longer than any bare shaft I'm familiar with. Now with my 175 gr. it looks like I need to cut....did I mention that I hate cutting carbons. One quarter inch too much and you're screwed! Oh well, if I screw it up I guess I can get one of the new cinderblock broadheads and become an UEFOC convert, lol!
 

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Assuming the same wall thickness, a shaft of larger diameter would be stiffer (static spine). Part of the static behavior (deflection under load) is determined by the second moment of inertia (I), one element of which is (outside diameter^4 - inside diameter^4) as seen on page four here...http://archery.berkeley.edu/wp-content/uploads/2011/08/KNSU-paper-by-Lieu-version4.pdf

The dynamic behavior of an arrow is addressed in the last half of the referenced paper and is a bit more complicated, although the second moment of inertia plays a part there too.

It's an interesting question. How it works in the real world due to the dynamics involved and the change in angle relative to the riser...? I guess that's why we just shoot bare shafts and fiddle until it's right.
 

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Although many may say just shoot the damn things and work from there I can understand all these arrow spine queries.

I have been lucky enough to be given several different spines and makes, but to spend your hard earned dollar on a set of arrows and find they will only work with 225gr up front when you're looking for target arrows or find they will only need 85gr points when you need some hunting arrows can be a big deal for some.

Not criticizing anybody, just saying. I know if I was in the market for a dozen mid range or top arrows I would be asking a few questions.
 

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Webster and Easykeeper, I don't doubt that I'm incorrect (never wrong, lol), but I think my reasoning is sound. RH bow and a "fat" arrow will point further left of center than a "skinny" arrow making the skinny closer to center shot.

Bowmania
 
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