@CEO of Gay I know a lot about the M40 mask we used the NATO C2 canisters for it. In regard to how effective it is against CS, it's 100% effective. Any exposed skin will get irritated, but you won't even smell anything. Soldiers, Marines, etc. do gas chamber training not toughen them up, but to build confidence in the equipment. Most military masks and cartridges are designed to stop shit that will kill you, like biological weapons. CS isn't shit. Once you realize how effective the mask is, you're less likely to panic when attacked with a chemical/biological weapon.
The most critical part of mask training is just getting it out of the bag, sealed onto your face, and cleared without fucking it up. The first 5 seconds is make or break, and people panicking fuck it up. There was almost always someone in the gas chamber that would and start screaming or running around trying to find the door. They would be forced to compose themselves, then don their masks properly. If it were a real attack, those are the people that die immediately.
No clue if the 3M masks would work, but I doubt it. If they did, the military/LEO would use them because they're significantly cheaper and lighter. I've been professionally fit tested with them half a dozen times and they do have a good enough seal around the edges, but protection would be totally based on the filter you attach. I don't know if 3m offers something that's good enough to stop CS without clogging.
I think most modern military and police us the M50 or some variant of it. I've never worn one but they look more comfortable and have a way better field of view. Funny thing is a lot of the protesters that actually buy a proper mask end up going with Israeli surplus because of how cheap it is.
