Modding Help So how do I make new guns now?

I found a tutorial on how to make new weapons but it's out of date. I tried following it but the tutorial tells me to do things that are no longer possible. I wanted to make a ridiculously over powered 1-handed assault rifle for fun.

 

Best way to learn is to look at vanilla items and tweak them to see how changes effect the outcome.

 

I started doing that but kinda' got lost!