I have just completed a spine check on my Easton ACC arrows. I was curious to see if having shot them for approximately 2 years whether the spine had changed. I suspected that there would be some change due to 'work hardening' of the aluminium core due to the continual flexing during release/flight. I used my spine checker and got the following values. New unused ACC 2.04 920 shaft deflection = 18.43 mm. Used ACC 2.04 920 shaft deflection = 17.39mm. So it looks as though they did stiffen during use and maybe they are too stiff for the rated poundage range (Easton white chart). Any comments?