JimPic is correct, you can get varying weights of brass/stell inserts to beef up your broadhead & FOC weight

Have you read Dr Ashby's reports ? he says the best setsups are greater than 650 grains, 190 Grain Grizzly broadheads and steel adapters to grossly load up the FOC on the setups - I'm becoming a believer by reading his reports, they all make sense

my future setup will hopefully be graphlex shafting and those big El Grande's and a 700 grain total weight arrow out of a 54# Zipper recurve