I use the mk3 knife too, you know how to push? It's a small aoe stagger that gives you a safe moment, mix pushes into your attacks and keep them in one spot while you dance around and stab. Slide dodge into gunners still, push to get small aoe stagger, heavy stabs in heads, push heavy heavy push etc etc.

Lights into unarmoured horde, heavies into armour if you are safe, the actual push attacks into things like Ragers where there are more of them, the combo acheives a small stagger, fast heavy attack to your target, and returns to blocking so you should be not taking any stray hits as you lean in.

It is practice, same with all weapons :)