Differences between the Vulcan models past and present ?

I am no expert, but I will give you my 2 cents based on my memory.

The original Vulcan went thru 4 mods, that basically are considered the Generation (Gen) 1 thru 4. AGT has now just recently released the Vulcan 2.

Gen 1 if memory serves had a "ping" issue and the internal rod that cocked the hammer was "weak".

Gen 2 fixed the ping, beefed up the connecting rod?

Gen 3 added the new stock? Maybe changed out the regulator (black vs silver on the older models) Evgeny of AGT sent me a new reg, no cost so mine is a hybrid.

Gen 4 I'm not real sure what they did on the Gen 4

The Vulcan 2, improved the trigger, added 2 inches to the barrel and the air tube.



Other guys that are more up on this can sure add or correct me on my summation. I have a Gen 2 and love it. I have put a new stock (synthetic) new regulator as mentioned above. Nice guns, for sure. Hope this helps and gets other guys to submit the real updates to straighten me out. lol.
 
I have a gen 3 in .25 and love the thing. Im sure you could do some web searches and get some more detail but basically FunGun covered it. 
I know there was a bleed screw on the gen one and possibly the gen 2 also. There was a lock on the breach that prevented mag cycling or something on gen one and on gen 2 if i remember correctly. These features are not on gen 3-4 Now for the most part gen 3-4 were the same with the exception of the moderator and adjustable but plate and I believe the trigger on the 4th was made of metal. 3rd gen and before were made of plastic. (I would of never known about it until I read about it and checked out mine. Its plastic, but I assure you it is some seriously strong stuff. I would of swore it was metal until I actually looked). Also there was a mount for a rail on the gen 1 then not for the 2nd. At some point during the 3rd gens they brought back the rail mount. I just happen to have one. I purchased mine shortly after the gen 3 release. Gen 4 still has the rail mount. Hope this bit helps.
 
I have Vulcan 2. Magazines are new design, previous generations had kind of hook, you had to insert by a certain angle and push magazine down

New magazine just slides in from the side.

Still not as easy to load pellets as Daystate or Brocock, you always have to play with spring tension to be in the right position to drop pellet in place, it has no stoppers like Daystate, Brocock or even Evanix has. 

But the biggest downside - still no double feed protection and magazine is fully covered, you have no clues it is zero or 10 pellets loaded when it's in the rifle.

From outside you can't see pellets, in order to check you have to cock rifle and remove magazine, if by any chance, it was loaded already you will double feed.

It's not a problem if you are shooting from the bench, but if it's for hunting and motion alarm starts beeping in the middle of the night I have to jump from my bed sleepy, grab rifle and run outside, next morning I have to scratch my head, did I load pellet or not... 
 
I have Vulcan 2. Magazines are new design, previous generations had kind of hook, you had to insert by a certain angle and push magazine down

New magazine just slides in from the side.

Still not as easy to load pellets as Daystate or Brocock, you always have to play with spring tension to be in the right position to drop pellet in place, it has no stoppers like Daystate, Brocock or even Evanix has. 

But the biggest downside - still no double feed protection and magazine is fully covered, you have no clues it is zero or 10 pellets loaded when it's in the rifle.

From outside you can't see pellets, in order to check you have to cock rifle and remove magazine, if by any chance, it was loaded already you will double feed.

It's not a problem if you are shooting from the bench, but if it's for hunting and motion alarm starts beeping in the middle of the night I have to jump from my bed sleepy, grab rifle and run outside, next morning I have to scratch my head, did I load pellet or not...

This may sound kind of goofy but what I used to do to remind myself if I loaded a pellet or not was I would set a coin by the airgun if it was loaded. This way when I came back to it I would know.