I disagree on the Greene. The operation is exactly as you describe, but the weapon is not fully loaded until the complete (but "inverted") cartridge has been installed - from that point on one is just continuing a (rather strange and overlapping - since the "cartridge" is basically useless) cycle.

While not explicitly stated, I believe the premise under discussion was that a complete immediately fireable round is in the closed chamber, ready for use, while the magazine is being refreshed. The Krag qualifies. Any Lee does as well.

This discussion usually omits the myriad qualifying .22s, as the capability is normally cited as an advantage when dealing with dangerous game - number of legs not specified.