As mentioned above, this is actually working as intended.
Does it make sense? No.
Is it useless? Yes.
Has it been mentioned several times? Yes.
But it’s still as the developers envision it, apparently.
I think every single player of GZ would like the exp. 12G to work as the FNIX hunters’ Flechette gun (where the ammo type instead only would have impact on the “spread” of the flechette rounds), but I don’t have any hope that’s actually going to happen… 
It was the first experimental I picked up, and it didn’t exactly make me happy. After making a lot of noise about it, a bright person (Hi @kakarron) in here said “It is an experimental! Not all experiments are successful.”. That kind of shot me up 
And seen in that context it was actually quite smart of the devs to make it that way.
Right, that’s a very valid point. It would be ok if it had some disadvantages, along with its advantages.
Problem right now is it doesn’t hold any advantages over a normal shotgun, since I feel the damage is inferior as well (according to my own testing). If it had a serious damage boost, the disadvantage would be outweighed by increased damage, but that’s not the case now according to my experience.
You are right, @ameinild. I used it for a short while avoiding the useless slugs (red ones I think … can’t really remember). Eventually I put it back in the Plundra and haven’t thought much of it ever since. I have no idea what justifies its existence. The range is too short even to commit suicide 
That’s ultimately a serious bummer in a post-apocalyptic world overrun by killer-machines!
Merged threads that concern the 12G Experimental Shotgun. Since it may be unverified if it’s behaviour is a bug or not, I’ll leave this in Feedback/Feature Requests for now.
/Mod
How is it possible that the slugs in this shotgun are NOT like the IN REAL LIFE Gun the NeoPup.
I mean why would you not have the shotgun act like a semi auto long range direct fire grenade launcher… And why not have the birdshot act more like close-ish range staggering material. Like it is now but more stagger and lower range. As for the buckshot have it more range and more pellets and you are set on those. 
Is more fun for evreyone that way…
As far As I remember lurking in this forum, exp shotgun was ersatz-melee weapon before we got melee proper.
Now, I’d propose it’s total rework.