Why do people keep assuming the bolt is locked to the rear? Follow me here. Soldier picks up weapon, charges it (bolt ends at the forward position), closes dust cover, inserts magazine. In order to fire, Soldier must charge the weapon again to go “red.” Yes, it takes only a couple of seconds, but in an ambush, that can mean all the difference, not to mention, if you’re trying to be stealthy at all, it’s going to make a nice loud clacking sound that’ll give you away immediately.
This is a stupid policy, there is no reason for it, it’s idiot “leadership” trying to please other idiot “leadership.” If you can’t trust your Soldiers with loaded weapons, then you shouldn’t be sending them out the wire, period.
But if you hold the bolt release (on the opposite side of the button) when you charge it, the bolt will stay back. Then you can insert a mag, and just a touch on the bolt release will slam it forward and chamber a round. Keep the safety off and you're ready in a nanosecond. At least... that's the way I would do it.
I'm not saying it's the best way to go. All I'm saying is that it's not necessarily that big of a difference. By the time you could bring it up and get sights on a target, there would be a round in the chamber. All told... it just doesn't help much with AD's either. I'm not sure what they're really trying to accomplish other than some BS PC news bite.