If he charges it usually means he's not sure what's in front of him so he charges to protect himeself and scare off an attacker. Remember their eyes are on the side of their head and while they do have excellent vision for the most part there is a blind spot in front of their face. Try to approach him from the side so he can see you.

Buns usually bite as a defense or when they want you to leave them alone.

If he hasn't been neutered yet, please do so. It will calm him down and he will be more managable and sweeter to you.