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Author Topic: Heavy bows? Spine rating of shafts outside the AMO standard?  (Read 7146 times)

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Offline markinengland

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Heavy bows? Spine rating of shafts outside the AMO standard?
« on: September 14, 2008, 06:28:03 pm »
Does anyone know of guidance for spining arrow shafts for bows of over 70lbs?
The standard shows  a deflection of .37 to .35 of an inch for bows of 65 to 70lbs (band K). What if the bow is heavier or the shafts stiffer?
Mark in England
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Offline Pat B

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Re: Heavy bows? Spine rating of shafts outside the AMO standard?
« Reply #1 on: September 14, 2008, 08:38:21 pm »
Mark, I have a spine deflection chart that goes up to 125#(.208). If I can locate it and get it to scan I will post it here or probably e-mail it to you.  I believe there is a formula to follow to figure it out but I don't know it. I'm sure someone does and will speak up.     Pat
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Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline markinengland

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Re: Heavy bows? Spine rating of shafts outside the AMO standard?
« Reply #2 on: September 15, 2008, 03:58:55 am »
Pat,
Thanks. If you could find it that would be great.
Mark
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Offline Pat B

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Re: Heavy bows? Spine rating of shafts outside the AMO standard?
« Reply #3 on: September 15, 2008, 12:02:11 pm »
Mark, I couldn't get it to scan  ::) so I copied it for you and sent it in an e-mail to you. I hope it is what you want. I also sent you to a link that might have the complete chart.    Pat
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Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline Badger

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Re: Heavy bows? Spine rating of shafts outside the AMO standard?
« Reply #4 on: September 15, 2008, 01:12:50 pm »
Mark, on some of the heavy bows that are using 32" arrows and 300 grain bodkins the spine might be kind of hard to figure, The point weight has a major effect on how much spine you need as does the length. A 125# bow would need about 125# spine arrow if the arrow were 28" long and the tip about 125 grains. For every 25 grains point weight and every 1" of length you need to add about 5# of spine. So you might need close to 200# spine for a war arrow. Be real curious what methods our war bow enthusuasts use to get correct spine, good question Mark. Steve
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Offline Pat B

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Re: Heavy bows? Spine rating of shafts outside the AMO standard?
« Reply #5 on: September 15, 2008, 02:23:02 pm »
Seems I read that specific spine weight is not critical with heavy weight war bows. I don't know if it is the case or not. I can't pull a war bow anyway.  ;D      Pat
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Make the most of all that comes and the least of all that goes!    Pat Brennan  Brevard, NC

Offline Albert

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Re: Heavy bows? Spine rating of shafts outside the AMO standard?
« Reply #6 on: June 09, 2021, 09:59:42 pm »
AMO Spine formula (based on arrow deflection measured in inches; arrow supports 26" apart, 2 lbs weight applied in center of span):

spine in pounds = 26/measured deflection in inches

ex.:

   measured deflection = 0.500"
   spine = 26/0.500 = 52 lbs spine

   measured deflection = 0.250"
   spine = 26 / 0.250 = 104 lbs spine

and so  forth

Cheers,
Bert
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Offline Yooper Bowyer

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Re: Heavy bows? Spine rating of shafts outside the AMO standard?
« Reply #7 on: June 10, 2021, 08:17:25 am »
Good to know.
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