what happens when
 

i can understand what could happen if an arrow is under spined but what bad effects happen when there to stiff?

RE: what happens when
 

I think that they can shatter just the same as if you are underspinned. Someone that knows a lot more about bows than I do posted that a while back if I'm not wrong. I really am not sure what goes on that causes it to break. I'm guessing its because the arrows can't flex if they are too stiff so they just break? Ah I'm done making a fool out of myself someone will give you a good answer sooner or later :)

RE: what happens when
 

Shooting an over spined arrow is not dangerous at all. Many people do it on a regular basis with no problems.

The issue with overspined arrows is that they magnify form flaws and equipment setup problems. Out of a properly set up bow, they will fly just fine, however they will have a tendancy to wander if you don't do your part.

As a general rule, you should really try to get your arrows spined properly. This will give you the most forgiving arrow setup for your bow. If you can't get them spined perfectly, then you are better off being overspined than under.

RE: what happens when
 

I agree with this, but I have one more tip for you to get the best accuracy. There is a machine out there that can determine where the spine of the arrow is. At the spine, the arrow is thicker. As you might have guessed, perfectly round carbon shafts do not grow on trees, companies buy carbon fiber in sheets then cut and mold the material into a shaft. Where the ends of the carbon fiber overlap, the arrow will be slightly thicker than the rest of the arrow. This is the spine. If you can figure out where the spine on your arrow is, you can fletch it accordingly. In this way, the spine of the shaft will always be in the same spot when you put it on the rest. I like to line the spine up with the cock feather. I wish that pro-shops and manufactures would do this without being asked, but they won't. You will need to ask. This will only make a difference if you are already shooting 300 in the range. Just a little tip. Take it with a grain of salt.