RE: shooting the spine out of an arrow?
I agree with Arthur (what a suprise), I don't think you can put a time limit on how long arrows will last. I can tell you what will mess them up quickly though. Heat or sunlight, carbons do not like direct sunlight or extreme heat, it will break them down from what I understand. I bet extreme cold is not that great on them either.
Lots of 3-D shooting for two reasons. One it generates heat as it stops the arrows and two is improperly removing them. If you wiggle them back forth to get them out it will eventually ruin them. Same thing with shooting them into a board or something. If you wiggle the arrow back and forth to get it out you could damage it inside. If you have seen a carbon that is warped at the tip ( has a light S shape to it) this was probably the cause. Also hitting them against other arrows, hitting something hard or glancing them off objects if you miss the target.
If you are going to shoot a lot of carbons I suggest investing in a good spin tester and use it often. The first time I shot indoor leagues someone brought one to one of the shoots. There were a lot of carbon shooters (expensive ones at that in some cases) that were pretty suprised and dissapointed when they put thier arrows on it. Then I threw my cheap easton Jazz youth arrows on there and they spun perfect. One guy was a bit PO'd at that.
Heck some carbons are bad right out of the box, do enough searching on this and you will see some posts on it. I hear about it most with Gold Tips, but they sell a lot of arrows so that makes sense. I will give them credit, they stand by their product and will replace them. I have read in some cases almost half the dozen did not meet specs right out of the box.
No matter what I shoot carbon or aluminum when I get new arrows I test them all out for groups and then how well they shoot with a fixed blade. The best three or four arrows out of the bunch I set aside as hunting arrows and don't use them again once they are tuned. The rest I use for practice or target shooting. A field tipped arrow is pretty forgiving if you use enough fletching on it.
Paul