not quiet? If noise is the problem, with an M4 format, one simply holds back the charging handle and let the forward assist do the work. With the older SP-1, M-16, Armalite system, no forward assist, easing the bolt carrier forward was a little trickier but you just stick your finger in it to slow it down. But waddling out of the water isn’t a quiet thing anyway. That first shot will let the whole neighborhood know you’re there.
True. I assume the idea would be to get into place as quietly as possible before that happens, if at all, and then begin to egress before a response can be mounted once whatever objective is achieved. Three or four bolts slamming shut does not seem to serve the "quiet" part.