Sci fi and fantasy guns

[AdAstra2009]

No one in their right mind would think that's real or based on a real weapon.

That right there negates the BFG on IMFDB, even the film version.
They fired off balls of green plasma, no-one in their right mind would think that is real!!!
Stuff like that is akin to Alien Death-ray guns.

The Eraser EM-1 fired off aluminum bullets or something along those lines according to what i've read so some people could conceivably think it was a real gun.