guns that don't suppress (or suppress well for reasons, say FAL)
FALs and other op rod guns are worth suppressing, but they'll never be technically hearing safe as gas adjusted ARs can (ARs still snap me, so I still use plugs with them on the range, but can tolerate a few shots without ear pro). FALs do need the gas plug modified, though, or they'll beat themselves to death with a can.
But that's the difference. My FAL para carbine was not tolerable with just earplugs without a suppressor, still too loud. Needed good quality full muffs for that, as well as other shorter barreled rifles. With the suppressor getting the FAL into the mid-140s at ear, though, the additional 15-20 dB reduction of foam plugs is plenty, and there's no concussion or flash.
I'm 39 now, and I wish someone had got me into the suppressor game a lot sooner, as well as warned about the damage from work environments and such. I wear ear plugs all day around my machines now, when running pressure washers and lawn mowers, using wet/dry vacuums, and everywhere else I can to preserve the hearing I still have, which has not been great in my right ear since I was a little kid due to ear infections. And as much as it pains me, I won't let my kids have cap guns because I know what the 140-150+ dBA report of those things will do to them.
M1 Garand and M1 Carbines aren't practical to suppress (so I've heard), and I have some other old tube fed 22s that I wouldn't thread
M1s can be done, but there are issues not to be overlooked. You can't just thread them and go to town, as the increased gas will bend an op rod just like hotter loads do.
On the tube mag .22s, there is a QD option for rimfire cans (Gemtech QDA, and there's another 5 lug critter I don't recall the make of), and I'm actually trying to find time to develop a smaller diameter rimfire can that will clear those tubes. But then, 22"+ .22 rifles really don't need a can. It does make them whisper quiet, but the report of a long barreled rimfire just isn't that much with a naked muzzle. I haven't threaded my Marlin 39A or 1897, as they're quiet enough with their 24" barrels that it's not worth altering them. But the 25" barreled Legacy Escort .22 with a can on it is ridiculous, just hear the firing pin click and the bullet impact.