Chances of an unfired round just "jambing" in the chamber, slide still in battery and striker cocked are non existent.
That is the order of operation for any semi or full auto weapon. You cannot skip ANY of the steps, or have one occur out of sequence. If the the weapon is cocked (step 5), and there is a live round in the chamber (step 6), it must have completed steps 7,1,2,3 and 4, in that order.
The only instance I have seen of a live round in the chamber being "jambed" is with several Beretta 92F's. These were caused by broken locking lugs disallowing the slides' cycle. The rounds themselves however were not jambed, and the pistols would have attempted to cycle per the above sequence should attempts to fire them have been made. The only way to fix it is to take it well away from anyone and remove the slide, broken locking lug, and barrel.
So as stated above, rack the slide for a live round in the chamber and a cocked striker.