I'm not the best person to answer, I am a layperson...
but the board is quiet, I shall have a try.
The terms "sociopath" and "psychopath" have now been joined together under Anti-Social Personality Disorder... here:http://en.wikipedia.org/wiki/Antisocial ... y_disorder
ASPDs are more likely to be self-aware. They realize early on that they can't "read" others' emotions (and do not care to). So they adopt a sort of script, they "become" a normal person, they adopt that role. Then, if they choose to, they can still manipulate, gaslight, etc, as NPDs do, but they sort of know they are doing it and as I understand it they generally believe it's fairly harmless.
Some become violent, most do not.
NPDs aren't really aware of what they are doing. They believe others need to be corrected because they haven't recognized the truth, and that truth is that the NPD is superior 100% of the time.
You might want to read up on Malignant Narcissism. This is the form of NPD where ASPD traits also come into play (in the form of self-awareness)... so then the narcissist can also be termed a sociopath. Some of my N relatives may be Malignant I think.
But others will do better at explaining this... (unreal...?)