quietly chambering a round? For what?
Lets just say a man was waiting on target X to show up on a trail. Target X was not walking as intel guessed, but was riding a fuel truck in front of an ammo truck. With the trucks were many, many other TOO's so said shooter dropped a mag of SB and unloaded the chamber very quietly and inserted an chambered a mag of specials. First rd opened the vessel, second lit it and ammo truck that was below and to the rear 25yds, TOO's and main target were tagged and the trucks were junk. Who's to say if he needed everything to fall in place except being able to re-chamber quietly or not?
I'll take the re-chamber quietly option every time.