If you step over the line from a semi-automatic AR to a full-automatic AR you face 10 years in prison.
...the N. Hollywood guys, if they had lived, would have 30 years and $750,000 tacked on for their 3 MGs.
I hardly think, given the nature of how that crime went down, that the NFA violations would have made any meaningful difference to their sentence. They'd have gotten the death penalty. So, pretty much, means life in prison (Cali).
...do these big sentences and fines get added to the sentences and fines of people who commit crimes with "real" illgeal weapons...
Yeah, they would. But you'd have a hard time finding examples. Crimes committed with NFA weapons are fantastically rare.