ORIGINAL: huntingson
If it is only one arrow though I would check to make sure it is not the same arrow every time. Then check the shaft and the broadhead. It is not uncommon, in my experience, to have a broadhead shaft (whatever it is called) a little crooked. A simple spin test can show you if it isa little off. Again, it is amazing what a rotating imbalance will do to arrow flight.
I agree 100%. This weekend bought 6 new muzzy 3 blade 125’s. 5 out of 6 flew great but the other one spiraled all over the place. I tried it on three different arrows and got the same results. I spin-checked it and sure enough it wobbled. The broadhead ferrule was slightly crooked. Definitely spin check that arrow that doesn’t fly straight.