I had a similar problem once.
It was the weirdest thing.
Turned out to be a bad combination of poor clearance off the rest, and broadheads that didn't spin true.
So the thing started out minnowing from hitting the rest funny, and then the crooked BH played off of the original interference and kept it from ever stabilizing.
The result was the coolest looking corkscrew flight I've ever seen.
-----~\~_ ~@_ _~`^^--=/~---> [

]
__________________
http://www.illinoisbowfishers.com
The truest measure of a man's ethics is what he does when no one is watching. -God
An unarmed man can only flee from Evil, and Evil is not overcome by fleeing from it.
- Colonel Jeff Cooper