Depends on how you define "close". 2 arrows of the same make and 'static' spine will have different dynamic spines depending on length of cut. And it is noticable. Typically long draw archers need to really get into the heavier Spined arrows so their arrows are dynamically Spined for a set up, even if that set up is the same for another Archer albeit the draw length.

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With all arrows longer length of the same spine will be weaker if all other components are the same. Don't need a robot as that's what a shooting machine does. If all other things are equal then length is what comes into play here.

 

going to give you some data. it may mean nothing to you. some of it is semantics.

arrow spine of an arrow is a static test. the spine of an shaft can be tested at 28" or 23" yes I said 23". not many people know this. there is math required for the 23" now this is a key point. what that means is static spine never changes. so an arrows spine say 300 is 300 wither the arrow is 30" 28" or 23".

now I do not know when or why we use dynamic spine when talking about the arrow being shot. even spine programs say dynamic spine. semantics here I come. when an arrow is shot it has a reaction. not spine a reaction. so look at the arrow as a reaction or dynamic reaction, but never spine when you are talking about it being shot.

now what effects this reaction. changing length. longer vs shorter will have a different reaction. changing tip weights or nock weight will cause a different reaction. improper bow set up will cause a different reaction. changing draw weight will cause a reaction. nock tuning is changing the reaction.

have you seen the ranch fairy tuning method. first off this is a trad tuning. its been around a very long time. what he is telling people todo is a reaction tune. this method he is using is for bows that are not tuned. horrible method but if a person has no ability to tune the bow then the method is a good one to use. but it is all a reaction.

some of the reactions you will not see. arrows that are spine stiff you wont see much reaction difference. meaning if a 300 spine arrow would work for you a 250 spine wont see much of a change if you shoot the 250 and just move tip weights or nock weights.

lots of things to think about when you start looking at reactions and asking questions about it.

 

Just because the arrow has a weaker dynamic spine [the longer arrow] does not necessarily make it less accurate.

Consider that on a given length, a greater FoC [based on center of mass] gives more effect to the fletching, then take two shafts of the same build only one is an inch longer... While the calculated FoC is slightly lower as a precentage, it is actually slightly farther from the center of length and therefore slightly farther from the fletch giving the lever arm between the fletch and the center of mass greater effect. If the bow tune was absolutely perfect and the fletch didn't have to correct flight it's not an issue, but if the tune isn't perfect and the fletch has to correct flight, the longer shaft will when all else is equal correct more quickly.

Regardless of tune however, a robot [or shooting machine] will put the same arrow into the same hole regardless of bow tune, and while the holes may be in different locations this isn't a measure of accuracy as you could sight into either shaft and the other would be the "less accurate" arrow; i.e. in the above example if the machine were sighted using the longer shaft, the shorter/stiffer reacting arrow would appear to be the less accurate one.

 

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