Dynamic Spine calculator. .NEW DOWNLOAD AVAILABLE

[Rob DiStefano]

i think the interactive chart is at least a decent starting point, but no chart is gonna even work up ballpark numbers for everyone.  i'm one of those anomaly "everyone" folks.

beman 500 shaft, 29.25", 350grs up front, 4" 4-fletch lo-profile feathers, 585grs all up weight, 55.5# holding weight @ 29".  bareshaft or feathered they fly just great at 5 to 35 yards.  plugging in the numbers to the chart yields the following ...

 

[wingnut]

Rob,

You might need to actually use the Other in the arrow shaft.  I found the carbon XXX to be rather bland.

Put you weight and spine # in the other and I bet it's closer.

Mike

[Rob DiStefano]

these are the numbers i get when using "other" - what am i entering incorrectly?

 

[James Wrenn]

Rob you are outside the norm.Most people could not shoot your setup at all.The numbers on the chart are probably pretty close but you still have to add in the human factor as you show.Sometimes things just work different.  

BTW..It would be almost dangerous for me to shoot the setup that works for you.That unknown human factor again.  

[Rob DiStefano]

Originally posted by James Wrenn:
Rob you are outside the norm.Most people could not shoot your setup at all.The numbers on the chart are probably pretty close but you still have to add in the human factor as you show.Sometimes things just work different.        

BTW..It would be almost dangerous for me to shoot the setup that works for you.That unknown human factor again.        

yeah, i'm weird - nothing i already don't know!    :D  

ooo, lemme add to this that in hunt camp other folks have shot my arras outta their bows (similar holding weights) and they also experienced those arras flying just great for them.  maybe i oughta patent whatever i'm doing, LOL!

[James Wrenn]

:D  
The spine on your 500s is about 65lbs amo.It llooks like you have less entered in your second screen shot.

[Rob DiStefano]

ok, i was using deflection, so here's what it takes to match my bow - 100 lbs! - yikes!

 

[metsastaja]

Snag thanks for the formula makes the calculator work for me. I did a lot of bare shafting a week or so ago and came up using 250' cut at 30" 100g insert and 125 points. Using that information the calculator did this.
 

[snag]

Rob, I adjusted your point weight for those shafts down to 160gr. and got 57 and 56.8  It looks like you would need much heavier spined shafts to be able to bump up the tip weight to 350gr.  You could put in a spine weight for Beman 400 or 340 and see how that works for your setup.

Les, looks like you are right on! Isn't it a beautiful thing?!!  

[Rob DiStefano]

Originally posted by snag:
Rob, I adjusted your point weight for those shafts down to 160gr. and got 57 and 56.8  It looks like you would need much heavier spined shafts to be able to bump up the tip weight to 350gr.  You could put in a spine weight for Beman 400 or 340 and see how that works for your setup. ...

been there, done that - what would appear to be a correct beman shaft for my holding weight and arra length (400 and/or 340) are just way too stiff and the resulting bare shafts fly at least a bit cork-screwy and land crooked. adding feather steerage helps heaps. i can consistently bare shaft 29" 500's from all 3 longbows, 46-55#, with dart-like flight.  heck, if it ain't broke ...  :D  

spent way too much time and money messing with carbons, and the only shafts/arras that work best for me are weak spined carbons.  an exception are the tapered ad's that fly well if over 600grs.

a few things have been of pivotal help with carbon shaft selection - reading about howard hill's arrow selection, shooting style, and his ability to reasonably accurately shoot anyone's arrows ... and jim ploen's iam articles on aiming.  this lead me to some aiming and form experimenting and though i can now shoot most any arra, it's the weak ones with enormous front end weight that work consistently best for me.  besides, beman 500's are cheap.   :D

[snag]

Well if you went with MFX 340s with 11gpi and 340gr tips you'd be at 56.7 and 56.8.  I am amazed that you can successfully bareshaft 3 longbows from 46#-55# with the same setup...but who am I to say different.

[metsastaja]

Snag: yes it worked well for me.      
I am going to try and build a couple of carbons
for 2 bows my brother is bringing down in a couple of weeks. Will be interesting to see how close I am.

[Rob DiStefano]

Originally posted by snag:
Well if you went with MFX 340s with 11gpi and 340gr tips you'd be at 56.7 and 56.8.  I am amazed that you can successfully bareshaft 3 longbows from 46#-55# with the same setup...but who am I to say different.

firstly and foremost, there are SO MANY factors involved in good arrow flight, including both the gear and the archer.  

the feller that designed this dynamic spine calculator, stu miller, did a really darn good job of averaging lots and lots of data, but to take any of the results as gospel is a stretch for anyone - you, me, or even ol' howard.

there are any number of factors left out of the equation - physical stuff that's difficult if not impossible to factor in because it's all too variable.  shaft material is one huge factor - static spine data for wood, alum and carbon can be intrinsically different and near impossible to compare within one set algorithm.  how 'bout degree of centershot, the length of the front end package (as it affects the arrow's pressure point), or how foc and feather types affect the paradox?  now add in the human factor - shooting form and shooting process.

none of this is to dis stu's neat interactive spine chart, but to advise stepping outside of the box a bit when matching arrows to both yer bow and yerself.  can't hurt.

[phil_des_bois]

Rob I'm with you, I shoot 28" MFX500 out of 55-60 bows with 300gr up front and they bareshaft pefectly.

[wingnut]

Rob,

You gotta remember the folks that are in need of this info are the ones coming on everyday asking "what arrow can I shoot off of this bow?"

This gives them a place to start other then someones elses guess.

Heck I saw a person the other day recommend a 2016 to a guy shooting a 40# Bear because he thought he should have more weight.  At least with the calculator you can get in the ball park before you go buy the shafts.

And how in the heck can those arrows be flying that well with that light of a shaft?  LOL

BTW it does cover degree of centershot quite nicely.

Mike

[Rob DiStefano]

phil_ - this isn't an "us and them" thing, it just is what it is, no more no less.  whatever works best is all that matters and we're all "experiments of one".  

mike - i'm totally with ya mike ... as i stated, the chart is a real good thing, particular for those new to trad ... for some of the rest of us ol' curmudgeons, we just may have other ways of skinning da cat.  :cool:

[wtpops]

I dont know what im doing wrong but when i put in my setup info i get a .3 as the first # and a 76 as the second. What am i doing wrong?

I use a Carbon Experss Maxima 250 with a deflection of .407 so i devied that by .825 and get .493, i plug that in and get that wierd first #.

[Rob DiStefano]

wtpops - the static spine deflection is in weight (pounds) not length (inches).  i dunno what the cem 250's equate to in pounds, someone will chime in for sure .........

[wtpops]

Dohh, i got it helps when you read the hole thread, found my answer on page 2. Thanks

[snag]

That CE Maxima has an equivalent spine of 77.4