its called a "hard" 360 because since you are turning slightly while grinding (40-50 degrees ish) you are actually spinning more than a 360 to do the full spin and land straight.
Tip is: think about it like you're learning 360's all over again and keep looking over your shoulder to spin the full thing instead of underrotating just doing a 360. balance on the feeble is the other key so you can get a good jump off the ledge/rail then its just trying more and more and more.
good luck!