It's possible, but it's layers upon layers of RNG stacked on you. You first have to get a blue engram to simply drop from the end rewards screen (it's not guaranteed), then it has to be the specific item class you want (primary, heavy, etc.), then it has to dismantle into a Legendary, then it has to be the specific legendary you want, and then it has to have a good roll. It's not worth the time investment.