Along the same lines, Ive been told never to drop the slide on an empty chamber in a 1911...what about that?
You can batter a good trigger job and ruin it unless you pull the trigger before dropping the slide. That keeps the hammer from battering the sear--which is what happens when firing the gun. That way, you just put unnecessary wear on the frame.
However, you obviously DO NOT want to get into the habit of placing finger on trigger of any gun before dropping the slide. Solution is to not be dropping the slide, except when loading, since rounds in the magazine cushion the slide enough to avoid problems.
When Wilsons test a gun for hammer follow on a combat pistol with nice trigger job, they drop the slide with one rd. in the magazine-- with trigger pulled, and once without pulling the trigger. If it passes that test, it won't follow during normal operation of the gun, since the finger would be on the trigger when the gun cycles, and, as mentioned, the slide slows down as it loads.
Real light trigger jobs (like two lb.s), on some competition 1911's are a whole other subject. They're difficult to do and easy to ruin.
Best way to drop the slide on a 1911 is with a full magazine. Lot's of cushion that way.
Modern .22 rimfires, many of them, will cause no damage by dryfiring, since the firing pin is stopped before it hits the edge of the chamber. Dinging the edge of the chamber is a bigger problem than damaging the tough firing pin on most .22's. Not saying it's recommended you dry fire any .22.
As far as using empty cases, they only last for a few firings. Better than nothing. I don't use the kind with the spring and brass "primer", I don't like the filings in the workings of my guns--especially revolvers. Look close, you'll see what I mean. I prefer A-Zoom.
I've been dry firing rifles for a long time without problems. Not to say that some A-Zoom dummy rounds wouldn't be a better idea.