You've got to get him to replace the hitting behaviour with something else. I believe you that he's not in control, and hence punishment/disapproval, short sharp shock tactics etc won't fix this.
The problem is how, then - because whatever is triggering it is going to get worse as he properly enters puberty, and quite apart from the fact it's obviously already upsetting (to you and to him), as he gets physically bigger and stronger, he could really do somebody some damage and potentially end up in trouble with the law.
Is he motivated to change it himself if you speak to him when he's calm or does he not think it matters because he knows you'll forgive him?
The reason I say replace is that like others say, being in a fight-or-flight reaction does not give a person time to think logically and step back down from the situation. He's not going to have the capacity to take that impulse and boil it down to nothing, so he needs something concrete (and realistic) that he can replace it with. Preferably before he reaches boiling point in the first place. I have read BTW that replacing an urge to hit a person with hitting walls/punching bags/pillows is counterproductive, because it's not replacing the hitting urge itself, it's just redirecting it - they've still got that automatic reaction to punch something, and hence one day there will be no punching bag/pillow/wall or somebody will try to help in an unfortunate way and so the person with anger issues will hit a person instead. It might work as an interim measure, but I think this is probably a situation you need to work through with a qualified therapist.
People who think this is about parenting or excess energy usually don't have experience of children with emotional difficulties. Most children will respond to a wide variety of parenting styles. I am certainly not strict, you could describe me as quite fluffy and feelgood, but my DS doesn't hit me, because he's able to understand normal behaviour cues and respond to them in an age appropriate manner.