Your arrow spine as TFOX and Jeff mentioned will caused your arrow to fly to the right (assuming) your releaseon your right hand. Underspined. 70# 29" DL, you'll need a stiffer shaft.However check to see is your broadhead sits flat on the insertand there's now 'wobble' if you spin test the arrow. Sometimes you have to switch the blades around and evenswap the washer.You also mentioned you got this broadhead from a buddy of yours, if it has been used it could have been damaged. Check the blades for any dings etc. A 70# bow will generate a fair bit of speed and a broadhead that isn't properly aligned will nail you tothe cross, most times.