I still don't get it :) ...

It is just misunderstanding :). I still think displacement vectors are a very nice concept, especially for melee. My post was more meant as "Why do you do this and that..?" because i don't fully get it. I also can say BrokenSword is a nice bot (he wouldn't be rank 9 if not) and i just wanted to understand why you do this and that. I think you are way more experienced than i am and so i thought there must be something behind it if he does it. 
I have no idea about guess factors (beside how they work) and therefor i have some difficulties to interpret displacement vectors, i guess. 

Looking at BrokenSword  again (sorry :)) it looks to me that you scale the vector on the current distance but did not adjust the resulting angle to the new distance. If something moves perpendicular to you, you would miss him, because you scaled on the wrong bullet ticks - or am i  wrong with this? I ask because this exactly the point where i'm stuck right now. 

I don't think PIF is the only way to go, i just dig through all the available knowledge about guns and try to find something that can support my ideas. I have spotted some weak points within my single tick gun and hoped the displacement vectors can provide some additional robustness. After playing the whole day with it, i gave up and ask the above questions :). Beside of that i think every concept has it pros and cons and there is no one way to do things :).

I hope i haven't offended you somehow, if so, please take my apologies for this.