This is a great thread because it reminds us that we have to be careful, lest there be a big unexpected noise. I don't think you can focus on this too much.
I bought a few 9mm inert snap cap dummys thinking I'd use them for Dry Practice. What I found was that the physical process of loading a "round", and then the vision of a "thing" at the top of my magazine when I chambered them, literally made my mouth run dry. I guess I'd become so ingrained at the concept of chamber checking and looking through the magwell for an empty hole. I just could not take it. So I ended up putting the inert rounds back in their packages and in my spares box.
All my Dry Practice is in an area devoid of ammo, and that will never have ammo. I have only one gun that I dedicate to Dry Practice (USPSA gun). I chamber check it coming out of the safe. I chamber check it every single time it returns to my hands, even though I just put it down 2 seconds ago. I chamber check it when I put it back in the safe.
I have a blue G19.5 for draws and manipulations. I still follow all four rules with it, even though intellectually I "know" it is a hunk of plastic.