I know that an under-spined arrow will flex too much when shot effecting accuracy. And in the extreme case, a severly under-spined arrow will explode. But what effect will an over-spined arrow have?

So is too much spine a bad thing? How will it effect arrow flight? Thanks.

It's best to be spined correctly for your setup, but if you err so it on the side of "stiff". Of course this assumes you are shooting a release where archers paradox is not an issue. The slightly stiffer arrow will recover from any bending quicker, maintaining it's mass right behind the point. On broadheads this can mean better penetration.

AH
you Have learned well Grasshoppa

Ditto what BG said. I've learned the hard way that many charts are off, i.e., they recommend shafts that aren't stiff enough. Assuming you're using a release, it's hard to be too stiff. Once I switched to a "too stiff for the charts" shaft, my BHs flew much better.

And I have had the opposite experience. What it comes down to is finding the right amount of deflection on an arrow for your particular bow. I like to keep my bow in tune with the proper arrow insofar as keeping the arrow passing as close to center shot as possible. Anything more then about 1/8 inch left of centershot is too much. I don't like to get right of centershot. This is with a compound, right handed, with release aid.

All this talk about "stiff" & "penetration". Kinda sounds like one of them gooooood movies