In Episode 123 of the manga is revealed,
Pig god can't be hurt by firearms
We know other S Class heroes can't be hurt by firearms, such as Zombie man. But we see an S class rival as Garou in his first stage, someone who is capable to defeat the weakest S class heroes, having to divert a large amount of bullets from a gatling gun and having his hands bleeding from that. Is it known which S Class heroes can't be hurt by firearms, and if there is any who can be damaged by them?