Before you go hogwild buying new arrows and such, try fletching a couple of your current arrows with 5" feathers. With all due respect to wwag, I disagree with trying 5" vanes. The blasted things are just way too much weight on the tail end of an arrow w/100 gn heads. 5" feathers are a good deal lighter than the 4" vanes you're using - which means they'll shift your FOC forward and provide much better steerage.