I changed my 4" vanes to 2" Blazers on my stock 29" arrows and seem like they fly better! Probally not much change in FOC from stock.But my 20%FOC arrows now I can tell they flight noticably better,maybe slower but a little cross breeze doesn't effect them like the others and they thump the bag target.Removeing the 12-15%FOC's from target I have to pull them with b/h,the 20% arrows I just unscrew the head sticking through other side before removing!