Have just watched the Blu-Ray again…
I noticed that during the “Let’s show this prehistoric bitch…” sequence, the GBs twist the front gun handle making the transparent barrel extend from inside.
Had never noticed this before and I’ve never seen it on anyones Proton Pack build or on the YouTube videos. Was just wondering if anyone else had spotted this and if anyone has attempted to factor this into their build successfully.
Holy crap
It’s actually a green lever by the “trigger box” on the rear of the proton wand. The barrel twist is just for looks.
Ya, you might notice some of the packs out there have very long barrels and some short for downtime, with slack on the red wire near the barrel end. That’s for extending it.
G
that would be the “make em hard” shot.
the front handle on the thrower rotated simply for the actor’s comfort. It has nothing to do with the clear tube extending. Dan Aykroyd probably twisted it in that scene just for visual effect.
to elaborate on what donkey 8012 said, there was a mechanism inside the thrower which was operated via the small green lever next to the trigger box. the tube would be pulled back in manually using the trigger tip to grab and pull the tube back in. this was not shown in the films.
Watch the scene in the Sedgewick just as they exit the elevator, Ray pulls his thrower and hits the small switch. Watch closely and you can see the clear barrel pop out 
oh and. . .
ROFL!
Completely uncomfirmed.
doesnt it make sense though?
I’m talking about real-life function, not intended screen function.
When they could easily just put thier hand on the barrel and push it in? I believe it’s to make the barrel look neat, I’m not sure it serves any purpose production wise. However, debateable or not you can’t just go off acting like something is fact when there’s no comfirmation.
That’d be like someone saying the gun body to a proton thrower is made from an old poleroid camera. Assumptions are just that.
you’re right i should have worded that differently as its a personal theory, not a fact or widespread belief.
surely however a barrel could be made to extend using a larger scale mechanism like on a ball point pen, there are many variations how to do this and with the correct springs and mechanism it could be done reasonable movie accurate, even if twisting it is done for aesthetics and the pop out bit is done separately,
it could be done as simply as a slot in the main pipe and a tab on the barrel that can be hidden next to the handle grip and slid along, the twist could be incorporated to lock it in place, with a spring to pull it back when the crip is next twisted
its something i want to experiment with
of course saying that it would still be difficult, and the original lever way is best i suppose…
suppose movie accurate was the wrong words their , actor accurate? maybe? poor continuity accurate?
Has anyone ever built a gun with a barrel tip that extends via the green lever? The linkage seems rather simple, that is, if the electronics will cooperate.
I would like to see that! 
Does anyone know of YouTube footage to confirm either way?
The green lever looks a but weedy to do such a job…
OMG that is freakin awesome. How come no-one has done plans for this???
thats cool ive not seen that video yet however, thats not quite how it worked in the movie. When the thrower is holstered, the barrel is supposed to be pushed in all the way back so that the trigger ring backs up or almost backs up to the barrel collar and then it should pop out quickly when the lever is pulled. I dont care for how the one in the video slides slowly, doesnt slide in or out far enough and is also retracted by the lever.
there are some members who have made the mechanism. Watch for a WIP thread from mburkit soon!
People have had too long to think about this…
welcome to the prop community.
This is what you call dedication to a hobby which not only benefits the community but is totally awesome if you love props.
No compressed air was involved in the use of the packs.
In the vid…
that front handle looks like its about to fall off.
Major wobble.
And another case of total protonic gun hook reversal.
