I didn’t post last night, because I wanted to check with my resident [del]gun nut[/del] firearms expert.
He told me that a Glock will lock the slide open after the last round is expended, and will not close with the insertion of the new loaded magazine. You have to hit the slide release to get the slide to go forward and chamber a round.
He said a 1911 on the other hand will chamber as soon as the loaded magazine is inserted.
I would have been a better trick if we saw him load the magazine one handed.