According to the currently available footage of Arma 3 Bohemia still didn't include the Reallife-feature of having one bullet in the chamber.
The actual capacity of a gun should vary if it has been reloaded while a round is still chambered. (30+1 as an example, so called tactical reload)
I know this is really a minor thing. But is a key element if handling with weapons and this shouldn't be missing in a military simulation.