Mostly agree - I'd like to add that 5.56 seems like a toy until you bring it inside to play, where it's an entirely different story... The first shot feels like someone slamming the switch off on your ears. I wouldn't think this is the cause of brain damage though. IMO the overexposure SEALs have to the modern warfare breach charge is a huge red flag.

The M16 platform has small projectiles, but there’s a lot of powder behind them.

They are pretty loud, more so if you’re to the left or, especially, right where the ejection port sits.

My guess for SEALs is the breaching charges play a big role. Carl Gustafs are notorious as well, but I don't know whether SEALs use them. US Army Special Forces do.

Edit: Yeah, I should clarify to say the M16 is more likely to cause hearing damage, but not brain damage. The concussive force isn't that bad.

As far as rifles go 5.56 is about as anemic of a round as you can get and have it still be fit for purpose in a military or defense context. You can't even hunt most things with it because it's not powerful enough. They only way these rifles are causing brain damage is if you're on the wrong end of one.

They are however incredibly loud. Being close to someone shooting 556 with a brake is a really annoying experience and I would not be shocked if there were follow on effects.

I mean you'll get hearing damage for sure but I'm just saying that's a far cry from cavitating your brain tissue.

Yep. Clarified my original comment a bit.