How do i know if im hitting my bag hard?

Never mind the effect on the bag. It's the effect on your conditioning and stamina that mattes. You'll know if you hit hard when you're actually in the ring with a like opponent who's trying to find out on you, if he hits hard. Work the bag for combinations and stamina and the KO's will come. If you try for a home run it usually doesn't happen. The home run will come if you performed technically first.