ORIGINAL: Matt / PA
AT first glance I would be inclined to say that youcould beOVERSPINED with 4" vanes and such a light field point....... (Remember weight in the rear or removed from the front will effectively increase your arrow spine)
Before you go crazy, try a 100 and then a 125gr field pt on them and see what happens.
Fishtailing can be attributed to roughly 275,000 different things from fletch contact, to grip torque , poor rest tune, arrow spine, etc etc.
Get everything to center and try different point weights.
Actually it's more like 275,050. Matt just missed a few. Ya have to forgive him. He's young and inexperienced. LOL.