It's not the shoot-er who gets beat up by the shock wave, it's the shoot-ee. For the shooter-er, all it is is muzzle blast (which ordinarily will have a shock wave associated with it). It's a pretty good thump but it's also directional. The bulk of it goes down-range along with the round. The crew standing behind the gun only get a secondary effect.
The largest artillery barrages in history were in WWI, some of which lasted months. If the gunners were susceptible, it should have showed up then. But it din't. Shell shock generally only gets to the guys on the receiving end.
“Shell shock generally only gets to the guys on the receiving end.”
Shell shock comes to those who witness the ghastly unholy effects of war on human beings. That would be those on the receiving end as you say. One of the many reasons so many vets from the various wars can’t/won’t talk about their experiences. Too painful. Life’s a bitch.