Arrows match Stu's calc with one bow but not another

[FrankM]

Arrows match Stu's calc well with my 40 lb. Sage, but not with my 45 lb. Grizzly. They paper, bareshaft, and broadhead tune correctly for each bow. Is there an explanation?

45 Grizzly - Dynamic Spine: 58.2 (Stu's Calc)
29.5” Gold Tip Trads 15/35
145 gr. field point/140 gr. Eskilite
20 gr. insert
3x5” feathers
Dynamic Spine:  44.8 (calc)
Total weight = 431,  423 (calc)
GPP:  9.37,  9.1 (calc)
FOC:  18.6% (calc)

40 Sage - Dynamic Spine: 57.8 (Stu's Calc)
29.5” Gold Tip Trads 15/35
100 gr. field point/Stingers
3x5” feathers
Dynamic Spine:  56.8 (calc)
Total weight = 364, 357 (calc)
GPP:  9.1, 8.7 (calc)
FOC:  12.9% (calc)

I don't know much about the specifics of either of those bows, but I would bet how the centercut measurement is entered vs actual centercut measurement might have something to do with the discrepancy?

On another note, Stus calculator never gets things right for me, UNLESS I have the Personal Form Factor set for my whacked out form!      

Bisch

[M60gunner]

I go along with Bisch on the center cut. That Bear may not be centercut. The calculator is a starting point anyway. Been using it since day one. In all that time had only one bow/arrow combo agree with it totally. Funny thing it was with wood shafts.

Originally posted by M60gunner:
I go along with Bisch on the center cut. That Bear may not be centercut. The calculator is a starting point anyway. Been using it since day one. In all that time had only one bow/arrow combo agree with it totally. Funny thing it was with wood shafts.

I have had consistent success with the "Calculator".  Almost always with woodies and generally lighter weight recurves and ASLs.

[The Whittler]

It's just a starting point the rest is up to you.

[monterey]

You need to measure the actual center cut of the bow.  Select the bow from the drop down if it's there but verify the actual center cut.

[JohnV]

Spine calculators are nothing more than a good starting point.

Originally posted by JohnV:
Spine calculators are nothing more than a good starting point.

I am familiar with only one "spine calculator" (Stus) and, for too many years it has been spot-on...not just close, but dead nuts......if you do your work and input appropriate variables (that relate specifically to your bow) it can get you more than just "close"...and then you can do a "minor tweaks" from there.  

[Longtoke]

I plugged in the stats of my maddog and the arrows I had tuned up for it and was amazed to see that the calculator was spot on!  kinda blew my mind

[dragonheart]

I have found the calculator very accurate as long as you do not guesstimate any of the variables.  Actually, measure your draw length when shooting the bow, weigh the bow at your actual draw length (might be surprised at what you actually are pulling at your draw), get centershot dead on.  When I have right data input, get right data output.

[FrankM]

Hmm, good points. I've had my draw length measured. The Sage draw weight measured at 28 and 29 and the cut on the Sage matches its specs. I haven't verified these things for the Grizzly as it's new.

[Rob DiStefano]

IMHO ...

any and all "scientific" arrow/spine/deflection calculators are ballpark only. NONE are going to be spot-on accurate for ALL bows and arrows.  there are just far too many parameter parts to the bow/arrow puzzle.  

a lot will depend on how you shoot, your form.  there is a reason why an archer like howard hill can take arrows out of a dozen different other archer's quivers and put them all into a pie plate at 30 yards.

i used to spend too much time getting anal over arrows 'til i let it all go and just built an arrow that works well *for me* out of all my bows, from 43 to 54 pounds *holding weight*.  

this is particularly true for carbon shafts that have a huge range of dynamic spine versus static spine.  all that matters to me is getting a good mass arrow weight for hogs (or deer), usually 10gpp - arrow total weight DOES matter, not too light or heavy, balance that to the bow's *holding weight*.  add in lots of helical steerage from large feathers and a truly razor sharp point.  then go kill something.  no critical fussing around with spine, arrow length, FOC, or LMNOP required or needed.

woodies are a whole 'nother story ....

[FrankM]

I suppose my question could be: Is it possible for both of my bows to have a different "form factor" for the calculator?

If so, maybe everything is correct.

If not, I may have an input error.

Of course, the answer might be "it just depends".

[Rob DiStefano]

Originally posted by FrankM:
I suppose my question could be: Is it possible for both of my bows to have a different "form factor" for the calculator?

If so, maybe everything is correct.

If not, I may have an input error.

Of course, the answer might be "it just depends".

door #3 - it will always be a "it just depends".

[FrankM]

I did have an input error. I've found my Grizzly is cut on center but Stu's Calc is set to -1/8". You can't enter in that field, so I had to compensate by making my strike plate .188.

This brings my dynamic spine to 50.2. Still 8 lbs. off but a lot closer than 58.2.

[Gooserbat]

It's worked for me a couple of times the rest has been way off.  Same bow and different shafts.