I can't address the 223 or the semi-auto, but I do have three H&R 243s and a CVA Optima Elite 243, all of the factory brass that's been fired in the H&Rs will chamber just fine in the CVA. As a rule, new reamers will be on the fat side of SAAMI specs so when they're sharpened, they'll still cut a chamber within tolerance, albeit slightly smaller. So I guess it depends on when in the life of the reamer the chamber was cut, when the reamer gets to the point that it no longer cuts within SAAMI specs, it's replaced with a new reamer that will cut a slightly larger chamber again, but still within spec tolerances.
The bigger issue is the flex in the H&R action, warmer loads will stretch the brass more than the same load in a bolt rifle, dunno about semi-autos tho.
This is the way I understand it, and that's the story I'm stickin to!!
Tim