There are several orders of magnitude difference between a 9mm handgun and a small artillery round. The difference is in terms of concussive force.
If you shoot a handgun with earplugs in, you hear a pop that sounds kind of like dropping a small ball bearing on a wood floor. You feel a shock in your wrists and a bit in your elbows, like high-fiving someone.
Now, you stand a few yards from artillery - and I’m talking Korean war artillery, not modern stuff. Also not talking about reenactment stuff; they usually just put a bit of black powder in there. I’m talking about small tow-behind artillery that you’d see at the Big Sandy Shoot (Google it).
You _feel_ the sound before you hear it. You’ll look for some shooting muffs to put on _over_ your earplugs. The concussive force comes through the ground, through the air, moves through your head and stimulates your eardrums from the backside. You feel your guts vibrate a bit. It feels like the ground moved under you, like you’re landing after jumping in the air.
And _that_ is an order of magnitude or so below what we’re talking about with SEALs here - those guys are placing explosive with a sticky backing on doors, and torching it off from not very far away. There’s stories from them of not being able to get physically “far enough” from a charge, and having to detonate it anyway because you’re in a freaking war zone. When a SEAL says “oh, this is going to fucking suck” before pushing a button, you know it’s real.
> Could this problem also be affecting civilian gun enthusiasts?
Since you are clear that you do not think that civilian gun enthusiasts could be affected because they
> shoot a handgun with earplugs in
I thank you for your service for sharing your advice on how to become invulnerable to gun fire. Without that I might have doubted your expertise on this issue of brain damage from concussive force