I've always like the headbutt as a weapon,but I've trained with people who would never use their head they feel that it's a bad move to impact your head.Sort of 'brains in here no bang, protect'.
How do you feel about butting as a weapon?
The thing that is tricky is training headbutts if you nut a bag you end up getting friction burns across your forehead - tres attractive!
If you nut a wall...
Best way I found was to get your victim uh I mean training partner to wear a skidlid (fullface) & butt that.
Happy butting
Cheers Jez