Arrows aren't spine checked at 31". Here; "The Easton arrow chart states use of a 28 inch span and a 1.94 pound (880 gram) weight."

Okay, the arrow is checked in the middle of 28".

 

I'm looking at the back of the box the arrows came in and it has different spines for the same dw at different arrow lengths. It lists a 350 spine at 31" and 250 spine at 29-30". The box also has different GPI for different spines.
I have 31" arrows that are 350 spine at 10.01gpi and the box has 250 spine arrows at 8.97gpi. So if I cut the arrows I have that are 31" at 350 spine and 10.01gpi does the spine and GPI not change?
I'm sure I'm way over thinking this I just don't want to cut my arrows and not be able to tune them for my bow.

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There is static spine and then dynamic spine.
The static spine your referring to will not change.
The dynamic spine, which accounts for any forces that change the reaction of the arrow when shot from a bow.
This would be overall length of raw shaft, tip weight, a bows speed etc
These all have an impact on how an arrow reacts in flight, thus changing the dynamic spine.


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I'm using Carbon Express Heart Attack arrows if that helps.
Should I spend a little more for better arrows?

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Your not going to see much difference to be concered about. Sounds like you bought a box store labeled arrow by Carbon Express.

 

If they shot ok before you cut them you will be fine

 

no spine change

 

G.P.I. = grains per inch as in weight and that will never change. It will change arrow weight as you remove length obviously. Also removing length will also effect dynamic spine as stated above and that will effect arrow flight in reaction to forces applied. Hope that helps you with your question.

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Your static spine, which in your case is 350, usually printed on the arrow will not change. This means with a weight of 1.94 pounds hanging in the middle of the shaft supported at 2 places 28" apart, the arrow deflected 0.350" from the downward force of the hanging weight. It is a reference to compare arrows. The dynamic spine is how the arrow flexes (reacts) when the bow string applies force on the nock and is effected by pounds you are shooting, cam design, arrow length, point weight, insert weight, added weights, string weight and to a lesser extent in reverse with fletching weight, nock weight and wraps. So cutting an arrow shorter will make the dynamic spine make the arrow act stiffer, I have through testing my 350 spine shafts determined that changes of about about 3 pounds per inch are common, similar to reducing 50 grains of point weight. You might be able to see this in the form of slightly increasing horizontal tear in paper testing if you shoot bare shafts through paper while adding to subtracting weight (turns in limb bolts). Your form has to be excellent to see this test. You can also see it in shooting bare shafts or fixed broad heads arrows against fletched arrows. Good luck, hope this helps!

 

Draw back your bow and have a buddy put a sharpie mark on the arrow where it is even with the front of the riser, This is a great spot to cut a arrow.

Then tune your bow to your new arrow length and get on with your shooting, you could get lucky and the arrow flight will not change but just check and tune if needed.

 

I appreciate all the help. I'll get these cut and retune the bow. I'd have to retune with new strings anyway.

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Yep, any equipment changes you have got to at least check the tune but if you are doing new strings and cutting arrows you are going in the correct direction by tuning the bow completely.

 

Just be aware using CX arrows in the feature they are not usually the spine that is labeled on the arrows.
For instance, their 250 shafts are not a 250 spine and more fall in the 400 spine range, varying between different models but labeled 250's.

The 350's are generally not a 350 spine and can range from a 300 spine to a 347 spine, depending on the different models but all still labeled 350

So, in short, the static spine is not necessarily what is actually labeled so don't be mislead when choosing an arrow.


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