technical arrow spine question... dynamic spine

[8KCAB]

I've been using the once posted dynamic spine calculator by Stu Miller to guide my arrow buying.

From the drop down list on the spine calculator, I inserted "carbon 400."  After some poking around it appears that not all Carbon 400 arrows are alike in gpi (I'm new to this.)  The drop down 400's appear to have a 9.1 gpi built into the formula.  My newly purchased arrows are 10.4 gpi.  Are you following me?

I chose "other" on the the dropdown menu and entered 10.4 gpi and used .4 as my deflection (Beman MFX 400's.)  When I enter .4 it gives me an AMO static spine of 65#.

When figuring the dynamic spine of the arrow, do I simply use the 65# that the program generated or do I have to call the company to find out what this figure is????

[James Wrenn]

Go with the carbon setting instead of other.Other is giving amo standards for wood arrows.That will not read the same as the carbon standard.Don't worry about the weight difference.It will be close enough to make little difference.jmo

[xtrema312]

I would calculate the weight as a separate thing and us the carbon 400 setting.  You can put in your own data if you know it.  Check out the third generation calculator with the extra info on spine numbers.  The calculator is great to get you in the ball park, but there are still other variables to consider and you don’t want to cut them off and find out you are not tuned. I have had a couple bows tune right on with the calculators and a couple were close, but not quire right.  

My personal method now is to use the calculator and put in all the variables for the bow.  I can then use shafts I have with weight inserts and point weights to try a combo matching the spine I get for the bow in the calculator.  If it doesn’t quite work out then I tune with point weights until I find what it wants.  Then I can put that back into the arrow side of the calculator to come up with an arrow spine the bow likes.  If I want new shafts I stay 1” longer on the shaft than what the calculator shows with the point weight I want.  I check with lighter than intended point weight for a combo matching the spine I came up with to check the calculator numbers.  If all looks well I cut down a little more and double check before making the final cut.