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spine - need help!

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stuckinthemud:
To avoid hijacking a thread, I'll post my question here. I have good Welsh legs, that is to say at 5'6" I am blessed with shortness! I draw 24" and my preferred draw weight is around 35#.  The arrows I have fletched so far have had sharpened tips, re-enforced with a triangle of bone or antler, so super-light-weight, and fine against targets - no hunting in the UK.  So, how would I calculate the spine for that - a 24" barrelled shaft with 2" feathers and a 1/2cm triangle of antler inserted in a sharpened tip bound with cotton soaked in ca  let into a shallow rebate (rabbet) ? I usually shoot elb

DC:
Because you have almost no tip weight your arrow is going to behave like it's stiffer so you can have less static spine. Your arrows can be lighter, faster. Like Pat said in the other thread it's about 5 lbs spine for every 25 grains of tip weight but if you do the math it says that you would want to reduce your spine by 25 pounds.(starting at a 125 gr tip) Your draw weight is 35# ,start 10# under that and minus 25# for no tip weight. That means that your spine should be 0#. Simple, and you get to use rope for arrows ;D ;D ;D This points out the problem with rules of thumb. The further you get from the norm, the less accurate they are. I would start with 30# and see how it goes. I read somewhere that Easton doesn't make shafts under 30# spine(I think) because once you're that low it doesn't make any difference.

stuckinthemud:
Thanks DC, that is really clear but how light an arrow can I go before its like dry-firing?

Pat B:
You can also decrease spine weight by adding length. Like I said in the other thread I shoot 30" arrows but my draw is 26" so I can start with heavier spined arrows and still get good arrow flight. There is probably a variable with shorter and longer draw lengths(under/over 28") but I'm not aware of what it would be.

stuckinthemud:
Slight digression but I cant reliably get my draw length locked in,  as I tire my draw shortens slightly, how do you keep your draw length dialed in with longish arrows?

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