What kind of straight fletching? Feathers will spin no matter what, they have a natural curve to them even when fletched straight. And I honestly think straight vanes probably spin to some degree as well, just not nearly as much.

I shoot either blazers or feathers with an offset, mine spine for sure.

Now that I think about it they all spin, otherwise with straight fletchings all your arrows would end up in the target with the same orientation and it would be nearly the same as it was when it left the bow. This does not happen. I have also shot straight vanes and had problems with field points coming loose after a few shots. This would indicate to me the shaft was spinning in order to loosen the head.

Paul