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Ok so bow has a ibo of 340. But with my current arrows 29.5 422 grain 340spine. The actual fps is 290 at 62lbs 29.draw. If I shoot a 400 spine through it it shoots 300 fps. Question is obviously at 62lbs and 29 inch draw is not going to be 340 so why base spine off of 340? When your bow with a 350grain arrow most likely shoots 310 or 300. So why not go of off that fps to choose your spine? So in my case that would be a 400 spine instead of normal ibo spine suggested on spine charts.

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The Impartial Archer
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Because probably what is happening is the arrow is flexing so much it's bending WAY more than it should........and then as it straightens back out that energy is adding FPS to the system. Just like taking something squeezing it between your fingers and then the energy flicks it way when it's released.

That probably will continue to happen right up to the point that the arrow snaps and breaks off into your arm.
 

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The actual speed that an arrow is fired is almost entirely dependent on the weight of the arrow. A very stiff arrow of the same weight as a very weak arrow will still shoot nearly the same speed, within a percent or two, as each other. Where the big differences are is with tuning and safety. It is very hard to tune to an arrow that flexes like a wet noodle and it's not a good idea to shoot grossly underspined arrows as they can break and cause serious injury to the shooter or people around them. Will your 400 spine shafts blow up and hurt you, not likely. Might you be able to get them to tune, yeah you might. Will they be as easy to tune as the 340s, probably not, especially with fixed broadheads.

For the people reading along and any potential new shooters, actual arrow speed does not mean that the arrows are reacting the same on the bow. A 500 spine FMJ with 300gr up front might weigh the same as a 250 spine Dangerous Game FMJ with only 125gr up front but the 500 spine FMJ will almost certainly break on the shot with that much weight up front where the 250 spine will be totally fine. It's not the weight of the arrow, and indirectly the actual speed of the arrow, that determines if it's safe to shoot, it's the spine.
 

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Hard to figure out what you're asking, but it seems like your thinking arrow spine is related to ibo speed. Ibo is calculated with 350 grain arrow bow set to 30 inch draw and 70 lbs. That's how your bow will hit 340 fps. Arrow spine is a different subject. That's stiffness of arrow. Lots of variables come into play when choosing spine.
 

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Shootin and Cussin
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That probably will continue to happen right up to the point that the arrow snaps and breaks off into your arm.
That's not going to happen unless the arrow becomes damaged through hitting something.

I think BigMike66 sums it up nicely.
 

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I interpret the OP's question to be:

All other factors being the same (i.e., arrow weight, point weight, nock weight, arrow length, draw length, etc.), since arrow spine depends on arrow speed, why not use the actual speed of the arrow coming out of the bow, rather than using the manufacturer's claimed IBO speed, considering that the claimed IBO speed can be a marketing number and is frequently not accurate? More succinctly: why use a probably inaccurate speed instead of the real speed?

The answer is: most people don't know their true arrow speed, and the IBO is a good approximation which is easily available for all bows.

JMHO
 

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I interpret the OP's question to be:

All other factors being the same (i.e., arrow weight, point weight, nock weight, arrow length, draw length, etc.), since arrow spine depends on arrow speed, why not use the actual speed of the arrow coming out of the bow, rather than using the manufacturer's claimed IBO speed, considering that the claimed IBO speed can be a marketing number and is frequently not accurate? More succinctly: why use a probably inaccurate speed instead of the real speed?

The answer is: most people don't know their true arrow speed, and the IBO is a good approximation which is easily available for all bows.

JMHO
Yeah there's a lot to it but generally the IBO is decent enough proxy for cam harshness/energy input to the arrow.If you tried to shoot your ACTUAL IBO that would probably be a touch more accurate but there's no reason to nitpick this aspect of archery -- the charts are a starting point.
 

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Discussion Starter #8
I interpret the OP's question to be:

All other factors being the same (i.e., arrow weight, point weight, nock weight, arrow length, draw length, etc.), since arrow spine depends on arrow speed, why not use the actual speed of the arrow coming out of the bow, rather than using the manufacturer's claimed IBO speed, considering that the claimed IBO speed can be a marketing number and is frequently not accurate? More succinctly: why use a probably inaccurate speed instead of the real speed?

The answer is: most people don't know their true arrow speed, and the IBO is a good approximation which is easily available for all bows.

JMHO
Yep this is pretty much what I am asking. Sorry my op was confusing. Why not base arrow spine off of actual fps for the bow and poundage you are shooting. If we were to do that everyone would possibly be shooting faster fps. Maybe tuning would be easier who knows?

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Sorry, just re read question. I thought spine charts used draw weight and arrow length. Didn't know any used ibo speed. I guess i haven't looked at many. I know with my specs i need stiff as possible and don't need a chart for my son's arrows.
 

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I interpret the OP's question to be:

All other factors being the same (i.e., arrow weight, point weight, nock weight, arrow length, draw length, etc.), since arrow spine depends on arrow speed, why not use the actual speed of the arrow coming out of the bow, rather than using the manufacturer's claimed IBO speed, considering that the claimed IBO speed can be a marketing number and is frequently not accurate? More succinctly: why use a probably inaccurate speed instead of the real speed?

The answer is: most people don't know their true arrow speed, and the IBO is a good approximation which is easily available for all bows.

JMHO
Arrow spine does not depend on arrow speed though. You can shoot a 600 spine arrow 300fps or you can shoot 300 spine arrow 300fps if the weight is the same. However, the 600 spine might break on you.
 

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Shootin and Cussin
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Sorry, just re read question. I thought spine charts used draw weight and arrow length. Didn't know any used ibo speed. I guess i haven't looked at many. I know with my specs i need stiff as possible and don't need a chart for my son's arrows.
They are based on spine and draw weight. Many now will add or subtract weight based on speed of the bow which takes into account cam design, brace height, etc.
 

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The actual speed that an arrow is fired is almost entirely dependent on the weight of the arrow. A very stiff arrow of the same weight as a very weak arrow will still shoot nearly the same speed, within a percent or two, as each other. Where the big differences are is with tuning and safety. It is very hard to tune to an arrow that flexes like a wet noodle and it's not a good idea to shoot grossly underspined arrows as they can break and cause serious injury to the shooter or people around them. Will your 400 spine shafts blow up and hurt you, not likely. Might you be able to get them to tune, yeah you might. Will they be as easy to tune as the 340s, probably not, especially with fixed broadheads.

For the people reading along and any potential new shooters, actual arrow speed does not mean that the arrows are reacting the same on the bow. A 500 spine FMJ with 300gr up front might weigh the same as a 250 spine Dangerous Game FMJ with only 125gr up front but the 500 spine FMJ will almost certainly break on the shot with that much weight up front where the 250 spine will be totally fine. It's not the weight of the arrow, and indirectly the actual speed of the arrow, that determines if it's safe to shoot, it's the spine.
I do not condone shooting an underspine arrow. but I have tested. the test arrow was a 500 spine at 26.5 " shot out of a 65lb apa m5. the 500 spine arrow had a 600gr tip. I shot once by hand. butt hole pucker factor was to great so second shot was with hooter shooter. no breakage. arrows dont break as easy as we think. now if damaged or a flaw in them yes. AGAIN I DO NOT CONDONE THIS. IT WAS A TEST ONLY.
 

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Arrow spine does not depend on arrow speed though. You can shoot a 600 spine arrow 300fps or you can shoot 300 spine arrow 300fps if the weight is the same. However, the 600 spine might break on you.

Sounds like the first sentence contradicts the third sentence . . . ?

Regardless, I still say correct arrow spine depends on arrow speed (among many other factors)
 

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Sounds like the first sentence contradicts the third sentence . . . ?

Regardless, I still say correct arrow spine depends on arrow speed (among many other factors)
Why? Just because an arrow weighs a certain amount, which determines its speed from a particular bow setup, doesn't mean it might not break when it's fired if it's grossly underspined. The actual speed that the arrow travels is only due to the weight. The spine requirement of an arrow has nothing to do with how much the arrow weighs. Bow efficiency, arrow length, point weight, weight on the back end of the arrow etc. all play a part in what spine you need.

So if your theory were correct, if you used a 200gr arrow to test your speed and it flew 380fps, you'd say that you need a heavier spine but if you shot an 800gr arrow and it shot 200fps you'd say that you would need a much lighter spine, even though the bow would not change from arrow to arrow. That makes no sense. Just because an arrow flies a certain speed does not mean it's stiff enough.

Again, a very light spine arrow can weigh a lot depending on how you build it. That doesn't mean that the bow won't bend it to a dangerous degree when it's fired.

You can use actual arrow speed to calculate your actual approximate IBO speed and use that number to more accurately determine your arrow spine but you can't just say that an arrow going 300fps means you need a 340 spine and 290fps means you can shoot a 400 spine.
 

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Go to victoryarchery.com ARROW GUIDE/OPEN SPINE CALCULATOR. You MUST consider point weight and should consider weight on the back of the arrow. As others have said it's mostly the weight of the arrow that determines speed. I built a 400 spine and a 350 spine the identical weight and the 350 was 3 fps faster because it absorbed more than the 400 which flexed. You haven't really stated what your goal is, but you would do better to invest in something like a 350 Victory 3dHV if you want speed.
 

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You can use actual arrow speed to calculate your actual approximate IBO speed and use that number to more accurately determine your arrow spine but you can't just say that an arrow going 300fps means you need a 340 spine and 290fps means you can shoot a 400 spine.
"You can use actual arrow speed to calculate your actual approximate"....so does the OP use his actual arrow speed to determine that he should/could use a 400 spine and risk hes underspined...or does he use his IBO and go with a 340 for other benefits youd lean towards with a stiffer arrow?
 

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Charts, at least the ones I use, also don't include metrics for actual draw length, which is another component of arrow velocity as it is released; and when looking at the Easton charts it is my assumption the spine changes for different IBO/bow speeds are just categories to represent a more or less aggressive cam profile... Another vote for go with IBO and my two farthings as to why.
 

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Charts, at least the ones I use, also don't include metrics for actual draw length, which is another component of arrow velocity as it is released; and when looking at the Easton charts it is my assumption the spine changes for different IBO/bow speeds are just categories to represent a more or less aggressive cam profile... Another vote for go with IBO and my two farthings as to why.
All the factors used by the spine charts, are inputs for estimating the force of acceleration exerted by the string that the arrow shaft is subjected to, which causes the shaft to flex. It is this force of acceleration applied by the string on the arrow shaft that directly determines proper spine.

Put another way, adjusting arrow spine matches the mechanical impedance of the arrow system to the mechanical impedance of the bow system to maximize the amount of energy smoothly transmitted into the arrow at launch.

That's for a compound bow, there may be other factors at play for a recurve/traditional bow.
 

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"You can use actual arrow speed to calculate your actual approximate"....so does the OP use his actual arrow speed to determine that he should/could use a 400 spine and risk hes underspined...or does he use his IBO and go with a 340 for other benefits youd lean towards with a stiffer arrow?
The programs that are out there use IBO speed as ways to determine efficiency or "aggressiveness" of the cam system. Actual arrow speed is not the IBO speed, unless you're shooting 5gpp at 30" DL. You can use actual arrow speed to calculate your approximate IBO speed to use in a program on on a chart. The actual arrow speed should only be used to calculate the IBO speed though since that's what the programs and charts use. Now, if you're shooting IBO standards for bow/arrow specs, then yeah, use the actual arrow speed. The OP said he's not so he needs to calculate it.
 

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I do not condone shooting an underspine arrow. but I have tested. the test arrow was a 500 spine at 26.5 " shot out of a 65lb apa m5. the 500 spine arrow had a 600gr tip. I shot once by hand. butt hole pucker factor was to great so second shot was with hooter shooter. no breakage. arrows dont break as easy as we think. now if damaged or a flaw in them yes. AGAIN I DO NOT CONDONE THIS. IT WAS A TEST ONLY.

Jesse Broadwater shoots a 500 spine with 140 up front around 60lbs and prob 27.5” dl maybe and it shows underspined and he shoots it consistently. I shot a 330 spine out of a 65lb nitrum turbo at 30” dl and had 250 grain points(da-torch arrows) with no ill effects and tuned pretty much down the pipe.

Don’t usually shoot that but I did. Now I’m shooting a 300 spine with 300 grains up front, 60lbs and 30” dl. Bs perfect from my chill x.
 
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