who uses black widow's formula for wood arrow selection?

[Smallwood]

Just wondering who uses Black Widow's formula for finding which wood arrow spine you need vs the dynamic spine calulator?
I came up with two totally different spines using the two methods...
With the BW formula, I came up with an
70-75#spine.  
With the dyn spine calc, I came up with a 55-60#spine.
 
Huge difference in the two recommended spines for the same bow don't ya think?    :eek:    

I posted this on the widow wall the other day, and thought I'd post it here as well to see what response I get.
thanks,
sammy

[Benny Nganabbarru]

I'm not sure what the Black Widow formula is (I use a formula, but I don't know if it's the same), but the computerised calculator doesn't work for everybody, and I'm one.

The one I go with, and so far, so good, is from Danny Rowan:

- Draw weight at your length plus five pounds.
- For each inch of arrow over 28" add five pounds.
- For each inch of arrow under 28" subtract five pounds.
- If cut to or past centre, add five pounds.
- If using modern, low-stretch string, add five pounds.
- If using a point from 160 to 190 grains, add five pounds.

Although it wasn't on Danny's list, I would add that if you are shooting a modern bow with extra "oomph!" in the limb design (as compared to my Hill) you could add another five on straight away.

Even if this doesn't get you the perfect result you're looking for, it should put you pretty close, and give you an idea of whether to go up one group or not. So, you may wish to buy some test shafts based on and around the results of the formula.

This has worked well for me, and good feral animals have bitten the dust as a result.

All the best!

[Frenchymanny]

Same as Ben, right on the money

F-Manny

[trashwood]

I have had a shoulder injury so I had to go down in draw weight.  for a 45#@29" recurve, low stretch string, hot limbs, I use 60-65# spruce arrows.  I tune the bow with 125gr, 145 gr, or 160 gr  BH till it is down the center line.  

So I guess for a hot recurve I shoot 15# more spine.

I don't shoot a BW but I shoot bows that would be at least as efficient and fast.

rusty

[Three Arrows]

I think it's pretty close to what you need.  I have to go to 85+ for my Widow.  54#@28, 30" draw. I get weak spine using 80-85 cedars with 290 up front.  I use 30# overspine on a BW at my length.

[hkmp5]

Hello Sammy,
Something definetly sounds wrong with those numbers.  Pass along your details and I will double check the numbers for you.
-Stu

[Smallwood]

Arrow- wood shaft/27.0"bop/125grn pnt/14grn nock/5" feathers/ 48# amo static spine 12.2 gpi for port orford cedar 0.344 shaft diameter for 11/32" shaft dynamic arrow spine= 57.5# (55-60#)

Bow- black widow plv - def/ref longbow weight 54# @ 26", my draw 26", bow center shot-cut to center (I used +1/16" on the dsc),18strand  fast flight string, dyn arrow spine required= 57.4#

These numbers are ALOT different than with the BW formula of (70-75#)spine don't you think?

And don't get me wrong, I'm not saying either method is wrong, just amazed at the difference in them for the same bow setup.
I actually think the dynamic spine calc is the more accurate of the two.

[Don Stokes]

Smallwood, my spine chart developed by bare-shaft testing suggests you need 80-85# for a 28" arrow, for an unencumbered bow.

[Ham]

Smallwod, isn't that bow's shelf cut to -3/16"?

[BobW]

Ben's post of Danny's method works out almost the same as the Dynamic Spine Calculator for me....

Now, if I could just find a supplier of 105# to 115# 35" shafts........

BobW

[Smallwood]

Ham, it's cut to center, not beyond.
And with the strike plate, it measures + 1/16" from center.

[Smallwood]

This is Black Widow's method-----

"When selecting wood shafting you need to remember that spine tables still being used today, were developed years ago for self-bows of modest performance and calculated @ 28" arrow length.
Many of you will not be able to get a spine heavy enough for your modern, high performance bow."
To determine the needed arrow spine for your Black Widow...

1- Multiply the draw weight (at your draw length) by a factor of 1.4 (this factor is calculated for a Black Widow and may be too stiff for some other bows).
2- Next, add 10% spine per inch of arrow length Over 28" or subtract 10% spine per inch of arrow length Under 28".
3- If you are using points/broadheads heavier than 100 grns, Add another 1# spine for every 5 grains of extra point weight.  The arrow length is measured from the bottom of the nock groove to the end of the shaft/ BOP.


EXAMPLE-
54# draw weight @ 26" using a 27" arrow---------

1) Bow- 54# (X) 1.4 (BW factor) =                         75.6#
2) Arrow- 27" (-) 28" = (-)1 (X) 10% (X) 70 =     (-)7#
3) Point- 125grns (-) 100 = 25/5=                                      (+)5#
Approximate Spine needed =                                  73.6# = (70#-75#)

[Smallwood]