Insert a loaded magazine, rack slide to chamber a round,
remove magazine, replace that round, reinsert.
If you carry a reload magazine, you can save a move by
insert spare magazine, chamber a round,
replace with loaded magazine and holster.
add a round back to the spare.
Most IDPA and USPSA competitors will have an old magazine for a "Barney Bullet". Insert Barney, chamber a round, replace Barney with loaded magazine.
Note that all methods chamber that +1 out of a magazine, dropping a cartridge in the chamber and slamming the slide to snap the extractor over the rim is hard on the parts.