Ive used 15 grain washers before to go from 125 to 140 grains. All you have to do is spin test them to tune. If you get a wobble, play with the washer position a bit to get them to spin right. Ive even used teflon tape to help set the head right.

But I echo what has been said. You will have a better luck getting new broad heads. It will save you time tuning them.