[Chad C. Mulligan]

Cocking a pistol does not chamber a round.

It does if it's a Glock (or any other striker-fired clone).

[TexasGator]

“It does if it’s a Glock (or any other striker-fired clone).”

The trigger action ‘cocks’ the firing pin. If there is not a round already in the chamber there will still be no round in the chamber.