So, my understanding is that the reason the evokers look like guns is to elevate the user’s stress levels and essentially “scare” the persona out of them when they pull the trigger. And obviously, they don’t really fire bullets or the game would be over pretty quickly.
However, do they perform any mechanical function at all? Do they fire some sort of psychic energy, or make a sound, or anything? Or are they essentially just a metal frame with a spring-loaded trigger?
Presumably these questions also apply to Koromaru’s evoker collar, since it doesn’t seem to hurt him.
It’s never fully explained, but essentially they’re a machine that forces out your persona though unexplained techno-magic. The shape is just cheesy symbolism and is not integral to the summoning. Helps facilitate stressing the user out in a specific way and puts them in a mind state suitable for summoning a persona.