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Joined: Oct 2012
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With 47# recurve in for repairs, I decided to tune some carbons for my 57# recurve. For my draw length and that weight, all the charts and those I've asked indicate a 400 spine as the place to be.

Now, I reasoned that if I went up to a 340 spine (stiffer) shaft I'd still be able to get a tuned arrow by using a combo of longer shaft and heavier point, thus getting higher FOC and higher overall weight. Maybe making a fine adjustment using brace height.

I am wrong here?

Last edited by Gun_Geezer; 08/02/20.
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Correct - heavier brass inserts are an option as well. 3 Rivers Archery has a spine calculator on their site that will let you plug in your bow info and help you get a feel how shaft length, spine and point weight, etc. impact the dynamic spine. It's helpful in getting to a starting point on how much more point weight or shaft length you'll need going from 400's to 340's.

I'm shooting bows in the mid-50 lb range with 340 spine shafts at 29" with 50 gr brass inserts and 175 gr points. How your sight window is cut is a variable in the equation also. I cut my sight windows anywhere from right at center up to 3/16" past center. Past center allows you to shoot a heavier spine shaft.

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I've been using / referencing the 3R calculator. Amazing tool. Tried to us the "Other" shaft selection and it kind of blows up. They have an error in it someplce.

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You are correct. But unless you have a really short draw I would keep my arrows as short as possible. Stiffer arrows are going to more times than not hit on your riser and or rest.


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I have done exactly that when wanting to shoot a heavier arrow out of my traditional bows.

I prefer heavier arrows in the 600gr range when hunting elk, moose and using three bladed broadheads.

My shot distances are close, I cannot remember the last time I took a shot over 20 yards. So arrow weight is not factor in to arrow trajectory at short distances.

I have a few bows that are tuned for both 400 and 340 spine.

My favorites broadheads right now are Cutthroats for two blade and VAP's for three blade.


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One of the biggest variables is bow efficiency. I you can, reduce the centershot by going to thinner strike pad.
The 3Rivers calculator is a OK tool but lacks a lot of other variables that Stu Miller has on his later, and much better, version. I you can find it, it is the one that has variables for centershot, string, type of bow, arrow, etc.

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A quick search finds the Stu Miller calc here: http://www.taylortel.net/~rickbarb/dynamic_spine_calculator.html

Oddly enough, it has a few errors someplace:
- It does not recognize (gives error for) Beman Centershot 340 spine shafts.
- For Beman Centershot 400 and 500 shafts shows the ID to be 0.201 instead of 0.231". And recommeds, therefore, the wrong inserts.

Entering same data into both calculators yields excactly the same dynamic spine for my Bob Lee. For the arrow, the two calcuators differ by about 2.5. Hard to say which is more accurate. I note that both allow for "calibration" for my "form". In the end, I think they both give you a good starting point to set up your arrow and tune till it flies well.

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Interesting - I've used both the Stu Miller and 3 Rivers calculators and don't recall encountering any errors with the data I've used for both carbon and wood shafts.

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Originally Posted by JGray
Interesting - I've used both the Stu Miller and 3 Rivers calculators and don't recall encountering any errors with the data I've used for both carbon and wood shafts.

I didn't check anthing else. I'm setting up a bow with the Centershot 340's, so that is one that I tried. "Error". Danger Will Robinson!!!! The calc. does'nt seem to recognize it. At the bottom of the page it even states that the tool has a few bugs in it, or words to that effect. Still, nice tool.

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A selection of test point weights can come in useful in finding a balanced spine to point weight.


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Originally Posted by Hunterapp
A selection of test point weights can come in useful in finding a balanced spine to point weight.


I agree, and have 75gr-300gr for tuning purposes.

Last edited by CRS; 08/13/20.

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