Help! Can anyone shed some light on the different generations of the Vulcans? What I am looking for is the difference between a Vulcan Generation 2 and Generation 3 and Generation 4. I know the four has the adjustable butt plate but are there any internal changes, i.e. a different trigger etc. The difference between a gen 2 and a gen 3 would be what? Any help would be greatly appreciated. Thanks in advance.