Spine rule of thumb

[FrankM]

Another attempt by me to look for Rules of Thumb!    

Is there a rule like this that can ballpark spine for different arrows.

1. For arrows about .XXX spine, when you cut off one inch, you must add XX grains to the point to maintain spine. For example:
.500, add 25 gr.
.400, add 50 gr.
.300, add 100 gr.

[JimB]

I don't know Frank.I think it is going to be difficult to nail it down as precisely as you would like.Every arrow may be different and every inch may be different as the arrow gets shorter.

I did record,that on my 75/95's which are .340 deflection,that 18 grs of point weight changed spine about 5#,which should be close to the equivalent of 1" length.On my .300 spine shafts,it took 25 grs to equal 5# and roughly 1" in length.

[FrankM]

Yeah, I tried to use 25 grains on my latest experience with trying to tune my 5575's and 2018's, but 25 grains didn't hold up.

[lpcjon2]

IMHO I think using wood makes less math

[bornagainbowhunter]

Yup, Ipcjon2 is right.  The answer is wood.