My pistol has had a parts swap with an earlier Mk. II. My pistol can now fire with magazine out chamber loaded. Can I drop a 22LR cartridge into the chamber of a Ruger Mi. III 22 LR pistol — that is, will doing single shot shooting, by directly loading the chamber, harm its feed, extraction, or ejection? I ask because I remember that chamber loading some mechanisms is harmful.

I can’t see how this would hurt at all as the extractor is spring loaded. Plus we are talking about a small, thin brass rim. I can’t remember ever doing it with my MKII but I’ve owned it for 39 years…I’m sure I’ve done it. As a matter of fact probably with rat shot.

The only mechanism I am
Aware of that should not be single-loaded is a mauser or derivative that is NOT properly setup for it.

Of course you can.

Done it many times.