With the legacy system you can buy modifiable gear that can be transferred over characters. Well if you happen to have spare bm gear you can take those mods out and put it on the legacy gear and send it over to your alts. Keep in mind the Legacy gear is a bit pricy and so will taking out the mods of the BM and WH gear. So if you wanna grind out gear for your alts on your main, it is somewhat possible.