The functional difference between Bolters?

[Ilshavoh]

Campaign, if that isn't clear.

I'm looting "Bolt gun", "Auto boltgun", "Occulus Boltgun" from weapon pods.

Aside from specifically the sniper variants, I don't feel any difference except for the ammo count.

All of the guns that can be broadly categorized as "A bolter" all seem to do the exact same piddly damage and only vary in how often you have to reload. There isn't any greater/lesser kick, firing sound, anything that I can pick up without first going into a wiki dive or something.

I'm also not sure if the Bolt Pistol and Heavy Bolt Pistol have any real diff for the same reason.