Shout out to the Stu Miller Calculator

Beendare

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This is a great resource if you guys haven't tried it.

You can download it here;
Stu Miller's Dynamic Spine Calculator download page

Or you can use it on the 3 Rivers Archery site

So I'm working up to my old shooting weight and just didn't quite want to shoot 55-60# for the upcoming hunt seasons.

I settled on 50# and can shoot that with either my Morrison or Dryad ILF risers and my Inno limbs. ...30" draw.

So I plugged everything into Stus calculator and it came up with Beman MFX 340s at 31" with a 75gr insert, 150gr head- total weight 586gr. Dynamic Spine for bow came in at 60.4, arrow 63.2...you want these values to be within 2 or 3#.

On the Stu calculator a couple tips; crucial you enter the info correctly....READ the instructions. Even something like the strike plate being off by a sixteenth or your actual DL off by 1/4" will give you a bad reading.

So I bare shafted that arrow yesterday....Bingo, shoots right with my fletched arrows at 10,15,20yds.

Assuming you have decent form...and enter info correctly....I've found that Calculator to be right on the money. A time saver for sure when experimenting with different arrow configurations
 

LostArra

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I like to look at it after I have an arrow/bow tuned to my satisfaction. Sometimes it's close, sometimes not.
If your bow isn't on the calculator list I think it gets far shakier in its results.
"Generic" can vary quite a bit but this fits with Beendare's qualifier about precise input (garbage in, garbage out).
I do like to play with the arrow side of the calculator.
 
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Beendare

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I like to look at it after I have an arrow/bow tuned to my satisfaction. Sometimes it's close, sometimes not.
If your bow isn't on the calculator list I think it gets far shakier in its results.
"Generic" can vary quite a bit but this fits with Beendare's qualifier about precise input (garbage in, garbage out).
I do like to play with the arrow side of the calculator.

^ yeah, exactly.

Its really great when you can verify. So for example, there is no Morrison or Dryad 17" and 19" riser option....but the high performance recurve option is dead on from me with ILF limbs.

FWIW, When starting from scratch, I use it to get close. So maybe leave the arrow a tad longer....or experiment during tuning with different weight FP's to dial it in.

Then once you have that, you can tweak the personal form factor so its dead nuts match, keep all of the bow info the same.....and the other configurations of arrows with different point weights, etc are dead on for me.
 

sneaky

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That calculator wasn't even in the ballpark for my setup.

Sent from my SM-G955U using Tapatalk
 

Oz Bow

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Another shout out from me for the Stu Miller calculator.
I’ll echo others regarding it’s only as good as the data being supplied. Granted it may not cover every conceivable permeation it will cover most and at least get you close enough that some tweaking will pretty much buff out any remaining problems.

Sneaky I’m curious what you’re set up is?
Feel free to reach out via private message if you want.
 

sneaky

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Stalker Coyote, 53@30, drawing 31", right at 56# on my draw board. That calculator kept telling me to shoot 300 spines, running 275gr up front. I've set up enough stick bows I knew that wasn't right, and I confirmed it. 300s were ridiculously stiff. Would be a far more useful tool if they would actually update it, and add new shaft options. I don't even bother with it anymore.

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idkfa

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I'll resurrect this old thread, maybe someone else will find this helpful (as I did the previous posts here).
I used the calculator (both V2 and V3) extensively and got mixed results.

Case 1.
For my ILF recurve (70" AMO, wood/glass limbs, 45# @ 29.5", FF 10 strand string, entered as "performance recurve" into the calculator) and GT Valkyrie 500 (30.5" BOP, 34 gr fletching, 125 gr point, 12 gr insert, 0.75" @ 40 gr FACT system footing), the calculator was dead on.
These arrows fly perfectly at 3, 10, 15, 20 yards, and leave "bullet holes" in the paper during paper tuning.

Case 2.
Then I got into traditional archery, and things went awry. For my Bodnik Quick Stick (52# @ 29.5", 60" AMO), I found two arrows that fly well (as in, make a "bullet hole" in the paper):
1) Easton Bloodline 480 @ 30" BOP w/ 100 gr points and standard inserts.
2) Victory 3DHV @ 30.625 BOP w/ 200 gr points, Ethics Archery insert/outsert system weighing @ 225 grains (split as extra 70 gr added to the point, 85 gr as insert, and 70 gr as 1.1" footing).
The calculator predicts, however, that Eastons should be way too stiff, and Victory arrows should be way too weak.

My suspicion is that there's a substantial nonlinear component in the dependency of the dynamic spine of an arrow on the arrow components and its static spine (and quite likely material), which is currently not being taken into consideration.

Going slightly off track here, I am quite shocked that there have not been any substantially comprehensive attempts to model bow-and-arrow systems. Aside from a very convincing, but purely experimental study by Dr. Ashby in the '80s and a handful of hardcore purely theoretical papers in the late '80s/early '90s, there's nothing -- nothing conclusive, anyways.
It would be really cool to get the data from a ton of archers on their bow/arrow setups, plug it into a deep learning system, and build a model. I strongly suspect such an approach would yield very good results.

Edit: added Quick Stick details.
 
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Beendare

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IME, the Calculator gets you close....as in start with a longer shaft than you think and cut it down to fine tune.

The Stu Calculator is right on for my 64" bow [ 19" ILF riser, long limbs]..but its a little off for my 17" riser. I can tweak the data in to get it perfect but that form factor doesn't translate across the board.

Its hard to get the exact data input perfect with strike plate and such...then there is a wide range of bows that may not correlate to a very high efficiency recurve. My Uukha Vx's are about 10 fps faster than anything else....and do better with a stiffer arrow.

...
 

idkfa

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The calculator is an excellent (and so far the only!) attempt at predicting bow and arrow compatibility.

If the calculator were at least ballpark reliable all the time though, different arrows that work with the same bow would yield similar numbers -- but in my case, one is predicted to be way too stiff, and another way too weak. This discrepancy cannot be addressed in any way whatsoever.
This also led me to the conclusion that the model used to estimate dynamic arrow stiffness (note: regardless of the bow used!) has severe limitations.

To doubt my own arguments, I'd question them myself: are my release and my form any good?
Well, the calculator worked with my ILF bow beautifully (and I shot about 8K of those through that bow), and I've shot at least 2000 arrows through my Bodnik so far. FWIW, I believe the arrows I discovered work with it are indeed properly matched to this bow.

Point is, it's application has limitations, and unfortunately, those are not known or addressed in any way so far.
It appears it works well with ILF bows and arrows with middle-of-the-road stiffness (e.g. 0.500 spine or so).
It would do everyone a whole lot of good if there was a dataset with bow/arrow pairings and calculator results.
 
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