You can get brass inserts that weigh 100 grs,steel adaptors that weigh 75,100 or 125 grs,glue on or screw in broadheads from very light to 300 grs or so.You can very quickly get any combination of numbers that add up to at least 425 grs.Often there is space in a broadhead ferrule,ahead of the adaptor and you can add a few lead shot in there.#6 lead shot weighs about 2 grs per pellet.
The plus to all this is,a brass insert and steel adaptor have much more strength than the aluminum ones that have a higher rate of failure.