Do what you are doing at the moment, but just hangs the order up a bit. Spam the Mk.23 at the Scrake's head (I tend to use between 5-8), then pull out your M32 and flicnh the Scrake with a dud(one sht will do), then whip out your Scar and go to town on his head. You'll take a bit of damage (~17 armour is my usual), but a lot less than what you would if he used his swing attack.
Well, I try to get all of the the mk23 + scar damage in before he get in melee range. That way I tend to avoid damage. Although, honestly I need to visit the testmap and see what works best (at least conceptually).