SB,

You said you had a 300 grain arrow with a 100 grain tip. To me that means a total weight of 400 grains. Is that correct? If so, you are way safe on arrow weight in comparision to draw weight. If it means a total weight of 300, which I can't see you getting, then you are still OK. Like I said earlier, check for arrow contact. The arrow may be hitting the rest and kicking a little. The vanes are probably correcting the arrow flight quickly which is why you have decent accuracy. Also, you said your setup is accurate out to 40 yards. Is that with broadheads? Have you shot your broadheads? They will exagerate any bad setup you have. Sorry but I had to ask.