Why never match spine charts?

[Tedd]

My arrow set ups never seem to be close to the recommended spine using charts or the stu calculator. Before I mention what arrow I am using...
I'm curious what would you guess is the rights spine for this bow.?What arrow would you start with?
Target arrow weight around 650 grains.
Predator recover 61@30 3/4".

Thanks,

At 30 3/4"DL, I would guess at least .340, and maybe even .300.

Bisch

[damascusdave]

Without knowing the string material I would not even venture a guess...I find the string to be the most important factor when determining dynamic spine...I shoot 250 spine arrows with a couple of my bows at those specs...but only with fast strings

DDave

[Tedd]

I am using-
61@30 3/4" with an 18 stand bcyx string
.340 Three Rivers shaft
31 1/2" length
50 gr insert
250 grain point.

Any thing stiffer it will start to bump the side plate.

Spine charts and the calculator would put me solidly in the .300 range and with lighter points.
I'm just wondering if anyone else is that far off of recommendations?
I constantly test all spines shafts and the full range of points and length.  
Tedd

[Tedd]

[Leinsg91]

I shoot pretty close to you and 340s werent even close to stiff enough with 200 gr heads. had to go with some aluminum 2317s (easton gamegetter shafts) and they fly really well for me, but those put my arrow weight around 700 total grains. Packs a big punch but over your 650

[J. Cook]

I've had similar results - some of my arrow set ups for various bows fall right in line with the calculators that are out there, then others aren't even close.  I've come to realize every bow has a personality.  

Certain bows of mine actually shoot a wide range of arrows well, then others are so specific and picky that it was a nightmare trying to bare shaft tune them.